Posted by: oikosasa | July 18, 2014

Food flow across ecosystems

How much of nutrients found in a lake actually originate from that lake? And from the surrounding grounds? From the ocean? In the new Oikos paper “Broad sampling and diverse biomarkers allow characterization of nearshore particulate organic matter” Alexander T. Lowe and colleagues study the flux of food across ecosystems. Below is their own summary of the paper:

The flux of food across ecosystem boundaries has important consequences for biological community and ecosystem dynamics. Nutrient poor environments are often subsidized by more productive adjacent habitats. For example, a kelp forest can support animals living in a deep submarine canyon through the transport of dead kelp. In marine and aquatic ecosystems, detritus, or decaying organic matter, produced through photosynthesis is thought to break down and mix into the water. This particulate organic matter (POM) can then be transported long distances by water motion, potentially feeding organisms living far away from the original location of photosynthesis.

 

Researchers from the Friday Harbor Laboratories collect ‘raw’ POM samples. The complex mixture in these jars was dissected using counts and diverse biomarkers. Photo: A. Lowe.

Researchers from the Friday Harbor Laboratories collect ‘raw’ POM samples. The complex mixture in these jars was dissected using counts and diverse biomarkers. Photo: A. Lowe.

 

The origin of this organic matter is impossible to visually identify once the source has broken down into microscopic detritus. In coastal oceans this food source could come from land or sea. It is therefore common to use biomarkers like stable isotopes or fatty acids to track organic matter through food webs. This type of food source tracking depends on the assumption that each source has a unique biomarker signature that does not overlap the signatures of other potential sources. Using this ‘unique signature’ approach, studies have found high utilization of terrestrial plant detritus in freshwater lakes and coastal marine ecosystems. Similarly, kelp particulate organic matter has been traced into suspension feeders in an array of marine ecosystems. We were interested in the availability of different food sources to organisms feeding on POM. Most studies focus on the consumers, reconstructing the assimilated food sources using mixing models and the unique signatures. This method is often criticized because it does not account for natural variability in the source signatures, which is rarely measured directly. So we took a different approach. We looked directly at the POM to address this question; being a group of ecologists faced with a problem, we tried to count our way out.

 

An example of the complex composition of suspended particulate organic matter. Photo: A. Lowe.

An example of the complex composition of suspended particulate organic matter. Photo: A. Lowe.

 

Instead of assuming fixed signatures for each source, we made detailed observations of the living and detrital components of the POM and compared them to the stable isotope and fatty acid signatures of same sample. We took advantage of the natural variability of the coastal, temperate environment of the San Juan Islands, Washington, USA to look at food sources available. We expected the distinct seasons to be characterized by variable mixes of riverine, marine benthic and pelagic, and terrestrial sources of productivity. This broad sampling design allowed us to look at the relationships among the abundance of each POM component and the stable isotopes and fatty acid signatures under a range of natural conditions.

 

Nearshore suspended detritus in various stages of decay at Eagle Cove, San Juan Island. Photo: A. Galloway 2012.

Nearshore suspended detritus in various stages of decay at Eagle Cove, San Juan Island. Photo: A. Galloway 2012.

 

What we found was 1) a lot of unidentifiable detritus and 2) an incredibly strong correlation among both biomarker methods and the phytoplankton component of the POM. Detrital particles numerically dominated every sample, which meant standard cell counts (especially those that ignore detritus) were potentially missing a big part of the story. So we adapted a point count method to estimate proportions of each category of POM (but did cell counts anyway). Phytoplankton abundance alone explained a lot of the variation in stable isotopes and fatty acids. Incorporating changes in the phytoplankton community explained even more of the variation in biomarker signatures. This signature overwhelmed the non-phytoplankton detritus, implicating phytoplankton as not only a major source of ecologically important fatty acids, but also as a major driver of the variation we see in biomarker signatures. Taking this result a step further we were able to establish the relationship between the proportion of each POM component and the biomarkers often reported to ‘identify’ them. Information that is critical for selecting and interpreting biomarkers. This simple method provided more information about source contribution than the ‘unique signature’ method and allowed us to pick apart the ever-present detritus. We advocate this method as a way to improve the use of biomarkers in complex ecological studies and to start making cross-system comparisons in order to better understand food sources available to POM consumers.

 

Suspension-feeding POM consumers (dominated by Balanus here) in shallow subtidal habitats of western San Juan Island. Photo: A. Galloway 2012.

Suspension-feeding POM consumers (dominated by Balanus here) in shallow subtidal habitats of western San Juan Island. Photo: A. Galloway 2012.

If you haven’t yet heard the story of the body-snatching parasite lurking among wildflower populations across the globe, you certainly would not be alone. There is no need for alarm – it is a natural part of its ecosystem, and has likely followed its current hosts’ evolutionary paths for millennia. As such, it offers the opportunity to understand ecological, evolutionary, and environmental effects on infectious disease in wild populations, such as those responsible for many emergent infections threatening agriculture, wildlife, and human health. This is what the Early View Oikos paper “Elevational disease distribution in a natural plant-pathogen system: Insights from changes across host populations and climate”  by Abbate & Antonovics is about. Below, is the rest of the summary of the study:

 

Silene vulgaris plants infected with a pathogen that replaces pollen with dark fungal spores.  The flowers’ dirty appearance earned the disease its name, “anther smut”.

Silene vulgaris plants infected with a pathogen that replaces pollen with dark fungal spores. The flowers’ dirty appearance earned the disease its name, “anther smut”.

 

Darwin and Linnaeus were among the first to notice the affected plants with their dirty appearance and altered genders. The tiny culprit, a complex of species-specific fungi in the genus Microbotryum, and its lovely array of flowering Pink Family hosts, has since risen to prominence as a model system for studying everything from genome evolution to how parasites compete for hosts. The fungus works its way through the whole plant and into the flowers, where it takes over the structures that would normally produce pollen (or induces their formation in plants that were otherwise female!) – forcing the plant to produce fungal spores instead. Insect pollinators visit these flowers, whose attractive petals and sugary rewards often appear completely normal, and are tricked into carrying those spores to the next host. As this pollination process is how plants mate, the fungus is essentially a sexually-transmitted infection, behaving epidemiologically similar to diseases of humans or animals driven by either sexual or vector-mediated contact. An infected plant is not killed but sterilized, and has little choice but to keep flowering, year after year, propagating the insidious disease.

 

A bee visits a diseased flower, which is likely still producing nectar. Fungal spores will travel on the bee to the next flower, hopefully (for the parasite) a new host to colonize.

A bee visits a diseased flower, which is likely still producing nectar. Fungal spores will travel on the bee to the next flower, hopefully (for the parasite) a new host to colonize.

For one particularly widespread host, the bladder campion Silene vulgaris, endemic disease had only rarely been found outside of high-elevation European alpine habitats, despite its weedy presence across the continent. Many diseases are limited to particular habitats within the larger range of their hosts. The most obvious and arguably important example is malaria, which is devastating in the tropics but largely absent from latitudes closer to the poles. Many studies have predicted that as the global climate warms, malaria risk will increase in more densely populated temperate zones, largely in response to shifts in vector distribution. However, others have questioned whether rapid aridification may also reduce risk in currently affected areas with less public health infrastructure. As understanding disease emergence hinges on un-answered academic questions about what factors drive the distribution of disease, we set out to test whether the presence of our little anther-snatcher in Silene vulgaris was similarly limited by environmental factors. It was equally possible that the host populations were simply not as abundant or connected at lower elevations, or that not enough botanists noticed or reported the disease while cataloging plant occurrence.

 

A bee visits a diseased flower, which is likely still producing nectar. Fungal spores will travel on the bee to the next flower, hopefully (for the parasite) a new host to colonize.

A bee visits a diseased flower, which is likely still producing nectar. Fungal spores will travel on the bee to the next flower, hopefully (for the parasite) a new host to colonize.

To do this, we went to the eastern French Alps, recording host population locations, size, density, and of course, disease. Back in the lab, we were able to use the GPS point of each population to get their proximity to one-another, as well as summaries of climatic conditions. What we found was that indeed, despite being common at high elevations, the disease was exceptionally rare in populations below 1300 meters in elevation. Furthermore, the cool temperatures, high precipitation, and more stable climatic conditions of diseased locations explained this distribution even after correcting for the fact that disease was most common in larger populations, which were relatively more frequent at higher elevations. This study sets up the opportunity to investigate environmental, evolutionary potential, vector distributions, and host resistance effects on the distribution of infectious disease in a natural model species that poses little risk to human health, wildlife, or agriculture. Such studies will be crucial to understanding, and ultimately anticipating, how climatic perturbations may impact disease dynamics and emergence.

 

Janis Antonovics (study author), enjoying an afternoon refreshment along the sampling route in the small alpine village of Les Terrasses, France.  Citizens, farmers, and even sheep herders in the local community were always interested in why we were there, and often offered more than just water and lettuce from their gardens – they are a wealth of knowledge on the history, land use, and even biology of their local flora and fauna.

Janis Antonovics (study author), enjoying an afternoon refreshment along the sampling route in the small alpine village of Les Terrasses, France. Citizens, farmers, and even sheep herders in the local community were always interested in why we were there, and often offered more than just water and lettuce from their gardens – they are a wealth of knowledge on the history, land use, and even biology of their local flora and fauna.

 

A bee visiting diseased Silene vulgaris, complete with visible dark fungal spores at the tips of protruding anthers.

A bee visiting diseased Silene vulgaris, complete with visible dark fungal spores at the tips of protruding anthers.

Infected Silene vulgaris at the Col du Galibier, France.

Infected Silene vulgaris at the Col du Galibier, France.

The view of our study area from La Meije glacier near La Grave, France.  Pictured: Jessie Abbate (L), lead author; Kerri Coon (R), field assistant and undergraduate researcher.

The view of our study area from La Meije glacier near La Grave, France. Pictured: Jessie Abbate (L), lead author; Kerri Coon (R), field assistant and undergraduate researcher.

Shorter (ie, Twitter) version:

Fungal anther-smut disease in Silene vulgaris is restricted to host populations in high-elevation alpine climates.

 

Related website: Field assistant and undergraduate researcher Kerri Coon’s tumbler blog, documenting the 56 days she spent with me in the field tracking some of these populations. 56 reasons to be a biologist: http://kerri-lynn.tumblr.com/

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Posted by: oikosasa | July 10, 2014

Tuna-tern facilitation

How do seabirds use tunas to find more fish? Find out in the Early View paper “Facilitative interactions among the pelagic community of temperate migratory terns, tunas and dolphins” by Holly F Goyert and co-workers. Below is their short summary of the study:

In the Northwest Atlantic Ocean, researchers and fishers have been known to follow flocks of seabirds, particularly terns, in search of Atlantic bluefin tuna, Thunnus thynnus. We wanted to understand whether such “local knowledge” of tern-tuna associations, which has been described but not tested in the literature, is based on quantifiable community interactions. Marine biologists have speculated that these top predators have a commensal (i.e. mutualistic) relationship, such that terns benefit from feeding tunas, which draw attention to “bait balls”, then drive fish to the surface. We found positive, fine-scale, spatial and foraging (e.g. feeding) associations among tunas and terns (common, Sterna hirundo and roseate, S. dougallii), which supports our hypothesis that facilitation drives their ecological and behavioral interactions at sea, where tunas increase prey detectability and accessibility to terns.

 

common terns (Sterna hirundo) observed during a pelagic survey, 27 Sep 2006 (Photo:Marie-Caroline Martin).

common terns (Sterna hirundo) observed during a pelagic survey, 27 Sep 2006 (Photo:Marie-Caroline Martin).

The first author, Holly Goyert, observing for seabirds, marine mammals, and tunas during a pelagic survey

The first author, Holly Goyert, observing for seabirds, marine mammals, and tunas during a pelagic survey

Posted by: oikosasa | June 24, 2014

How do behavioral changes affect ecosystems?

That predators affect prey populations and vice versa is well known. But how does the prey’s behavioral responses to predators affect populations of the prey’s prey? This was studied by Bradley Carlson and Tracy Langkilde in the Early View paper “Predation risk in tadpole populations shapes behavioural responses of prey but not strength of trait-mediated indirect interactions”. Below is Bradley’s summary of the study and some photos from the experiment:

It is old news that different populations of the same organism often differ from one another in a number of characteristics. Populations may vary in color, size, morphology, behavior – just about anything. A common cause of such diversity is that populations face different environments that favor different traits. In particular, local predator communities (that is, how many predators there are and what species of predators) can be highly variable and can affect prey behavior. Where predators are abundant and dangerous, prey ought to behave cautiously by hiding, fleeing readily, or being inactive and secretive. When the risk of predation is low, prey ought to pursue opportunities to eat and reproduce.

My doctoral advisor, Tracy Langkilde, and I tested whether populations of wood frog tadpoles (Lithobates sylvaticus) from ponds with high predation pressure showed stronger behavioral responses to predators than tadpoles from ponds with low risk of predation. When they smell a predator in the water, wood frog tadpoles (like many tadpoles) typically become inactive, swimming less and hiding more. We think they’d rather be active so they can consume lots of food, grow large and fast, and turn into frogs before their pond dries. But, if there’s a predator around, it’s more important to not get eaten.

 

Wood frog tadpoles swim in a pond mesocosm.

Wood frog tadpoles swim in a pond mesocosm.

 

                We selected 18 ponds with wood frogs across Pennsylvania, representing a range of predator communities. Early in the year, I collected freshly-laid wood frog eggs to bring back to the laboratory so I could measure the behavior of the tadpoles. Later in the year (when tadpoles were swimming in the ponds), I used a net to collect random samples of animals from each pond. I’d then sort through the contents of the net to count the number of each kind of predator I found. These included dragonfly nymphs, newts, and other salamanders and insects. These data were used to assign each pond a value for how high the predation risk was; the more predators, and the more ‘dangerous’ these predators, the higher this number would be.

Brad Carlson uses a dipnet to sample a pond community.

Brad Carlson uses a dipnet to sample a pond community.

                But what about those eggs I brought back to the laboratory? We hatched them into tadpoles at a research farm at Penn State University and, when the tadpoles were old enough, introduced them to pond mesocosms. Pond mesocosms are artificial ponds, smaller than most natural ponds but big enough to be reasonably realistic environments. Our mesocosms were created by filling large cattle-watering tanks with water and adding standard amounts of dead leaf litter. We also added a small amount of pond water, introducing bacteria, algae, and other microorganisms which flourish and create functioning ecosystems. Each pond that we collected eggs from was represented by two of the mesocosms. One mesocosm had a cage floating in it, which contained a dragonfly nymph (Anax junius), voracious and hardy tadpole predators. Regularly feeding the dragonflies extra tadpoles in these cages ensured that the mesocosm water smelled of danger but that the experimental tadpoles wouldn’t actually be eaten. The other mesocosm served as a control (with an empty cage), allowing us to measure the normal, ‘baseline’ activity levels of these tadpoles. After a few weeks, I measured how active the tadpoles were by quietly walking around the mesocosms and counting how many tadpoles I could see (their ‘visibility’) and how many of those visible tadpoles were moving rather than still (their ‘movement rate’).

Brad Carlson observes tadpole behavior in mesocosms.

Brad Carlson observes tadpole behavior in mesocosms.

Our analysis revealed that tadpoles from ponds with higher predation risk responded more strongly to predators than tadpoles from other ponds, spending less time visible, and slightly tending to move less. A good explanation for this pattern is that tadpole behavior is adapted to local environments, with generations of selection in high predation environments ensuring strong responses to predators. This is interesting in its own right though not too surprising. What we really wanted to know was whether this kind of variation in tadpole behavior affects the pond ecosystem. In particular, antipredator behavior often leads to trait-mediated indirect interactions (TMII). In this case, the TMII is an effect of the presence of a predator (dragonfly) on the tadpole’s own food (periphyton, a film of algae and other microbes and detritus growing on submerged surfaces). Dragonflies shouldn’t directly interact much with periphyton, but they should indirectly via their effect on a trait of the tadpoles – foraging activity. If dragonflies cause tadpoles to be less active and thus eat less food, then their food (the periphyton) should increase in abundance. We expected, therefore, that populations of tadpoles that respond strongly to predators should produce larger increases in periphyton than less responsive tadpoles.

Pieces of filter paper with collected samples of dried periphyton (green and brown matter) from tadpole mesocosms.

Pieces of filter paper with collected samples of dried periphyton (green and brown matter) from tadpole mesocosms.

 

To test this we simply measured the mass of periphyton in the mesocosms by removing tiles we placed in their, scraping off the periphyton, and weighing it after drying. We found that, as expected, mesocosms with caged predators had much higher biomass of periphyton. However, the amount that periphyton increased when adding predators didn’t depend on how strongly the tadpoles responded to predators, nor did it depend on the predation risk in the pond from which the tadpoles came. In fact, tadpole behavior overall was a generally poor predictor of the amount of periphyton in the mesocosms.

This was unexpected, as we established a clear mechanism by which periphyton increases with predators (dragonflies decrease tadpole activity, decreased tadpole activity increases periphyton). Apparently, the amount the tadpoles actually eat is not perfectly linked to their activity: some tadpoles may become very inactive when predators are introduced, but still consume as much food as tadpoles that barely respond to predators. Do they switch their diets, or eat while hiding in refuges, or do most of their foraging at night? And, are tadpoles from ponds with more predators better at compensating for lower activity levels? These questions and more still remain, and will help us as we continue to try to understand how variation in behavior can impact ecosystems.

Posted by: oikosasa | June 17, 2014

Carbon flow between lakes and ground

How carbon moves from terrestrial food-webs to aquatic ones are studied in the new Early View paper “Boomerang ecosystem fluxes: organic carbon inputs from land to lakes are returned to terrestrial food webs via aquatic insects” by K. Scharnweber and co-workers. Below is their summary of the study:

The TERRALAC-project (http://terralac.igb-berlin.de/) ran from 2010 to 2013 and was an interdisciplinary project, based at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany in collaboration with University of Potsdam and Technical University Berlin. Five PhD students worked in five subprojects. The overall aim of TERRALAC was to study the effects of terrestrial particulate organic carbon (tPOC) on shallow lake ecosystems. We wanted to find out, how terrestrial leaves that enter lakes in autumn are actually processed with the lake food webs and we wanted to test this on the natural spatial scale.

Terra1

One prominent obstacle in studies on the effects and contribution of this allochthonous carbon on lake food webs is the problem of overlapping isotope values of the potential resources. Isotope signatures of the terrestrial carbon are often very similar to those of aquatic primary producers. TERRALAC chose a novel approach by using a tPOC tracer that is isotopically distinct, but also similar to the size and structure of natural leaves: maize (Zea mays) leaves.

Photo 1: Maize added into the littoral zone. The rope prevents it from floating into the open water.

Photo 1: Maize added into the littoral zone. The rope prevents it from floating into the open water.

In October 2010, we divided two small and shallow lakes, located in the rural area of Northern Germany approximately 100 km north of Berlin, in two equal halves. Both lakes are eutrophic and of similar size and depth. However, they have different alternative stable states: Gollinsee has turbid water and is dominated by phytoplankton, whereas Schulzensee has clear water and is dominated by macrophytes. We used plastic curtains to divide the lakes (Photo 1) from surface to bottom. With the help of many hands, we added the maize leaves into the littoral zone of the treatment sides of the lakes (Photo 2,3). By this approach we tried to mimic the natural input of tPOC by leaves in autumn.

Photo 2: Maize addition by hand in Schulzensee (October 2010).

Photo 2: Maize addition by hand in Schulzensee (October 2010).

Photo 3: Installation of the plastic curtain in Gollinsee.

Photo 3: Installation of the plastic curtain in Gollinsee.

Photo 4: Emergence trap used in our study.

Photo 4: Emergence trap used in our study.

In our article we present the flow of terrestrial carbon to lakes and back to its terrestrial surroundings via emerging insects (Figure 1). We focused on Chironomidae that have an aquatic-terrestrial life cycle and collected them as larvae, but also as adults using emergence traps (Photo 4). After emergence, they are known to become prey for terrestrial predators, for example for spiders that live in the riparian reed belts. Carbon isotope values of Chironomidae and spiders were significantly elevated in the lake treatment sides as compared to reference sides. As further demonstrated by isotope mixing models, contribution of maize was higher in Schulzensee, the lake where macrophytes are present. We conclude that structural complexity provided by the macrophytes may trap the leaves and by that enhance the food availability for the larval Chironomidae. In summary, we present the tight linkage between aquatic and terrestrial habitats and the cycling of organic matter across boundaries and borders.

 

 

 

 

Posted by: oikosasa | June 13, 2014

How does climate change affect pollination phenology?

What is climate change doing to plant–pollinator interactions? In the last decade, ecologists have focused on the possibility that climate change will shift the seasonal timing (phenology) of plants relative to their pollinators, reducing temporal overlap between interdependent species. In the Early View paper “Plant–pollinator interactions and phenological change: what can we learn about climate impacts from experiments and observations?” in Oikos , I evaluate the evidence that plant–pollinator overlap is changing as a result of climate change, and that such changes affect population persistence. I also discuss the strengths and limitations of different types of evidence for climate-change impacts. In particular, I explore the challenge of interpreting “temporal transplant” experiments, which manipulate the phenology of a subset of plants or pollinators in isolation, creating subpopulations of mistimed individuals in a matrix of unaltered phenology.

Observational data have shown us that, for the most part, plant and pollinator phenologies are advancing in parallel in response to warmer temperatures. While there are cases of plants blooming before their pollinators are active and consequently setting few seeds, there is no conclusive evidence yet that climate change is causing this “mismatch” to happen more often. There’s even less indication that pollinators are suffering from mismatch with plants—but pollinator fitness has received much less study. I suggest that there is much still to be learned about the direct effects of climate change (e.g., snowpack reductions, temperature extremes and fluctuations) on populations of pollinators and pollinator-dependent plants—effects that might be more demographically consequential than non-parallel shifts in phenology.

By Jessica K.R. Forrest

Forrest

Photo of male Megachile on unopened flower head of Erigeron speciosus. © J. Forrest

Many animals are breeding earlier and earlier in response to a gradually changing climate – but what happens when a species encounters a dramatically different climatic regime such as a complete reversal of the summer-winter rainfall pattern? In our article,  Phenological shifts assist colonisation of a novel environment in a range-expanding raptor, we explore this question by investigating how variation in the timing of breeding and breeding success of black sparrowhawks Accipiter melanoleucus relates to weather patterns during their colonisation of the Cape Peninsula of South Africa.

Raptors2

Heavy rain can have pronounced effects on breeding success in raptors, flooding exposed nests and potentially impairing the ability of parents to hunt. In the eastern and north-eastern areas of South Africa the majority of rain falls in the summer months and black sparrowhawks breed during the dry and relatively cool winter. During the last half a century a number of bird species have gradually expanded their range south-westwards within South Africa bringing them into contact with a dramatically different weather pattern: in the south-western regions the rain falls mainly during winter, a complete reversal of what occurs elsewhere in their range.

Raptors5

In the 1990s, the first black sparrowhawks were recorded breeding on the Cape Peninsula, in the shadow of the iconic Table Mountain. Rising to over a 1000m, this huge lump of sandstone generates exceptionally high levels of rainfall in the immediate lee of the prevailing winds, during the winter months as deep depressions roll in off the Southern Atlantic Ocean.

In 2001 a long-term study of the black sparrowhawk population[http://blackspar1.wordpress.com] on the Cape Peninsula was initiated. In the first year fewer than a dozen nests were monitored but as the population expanded so did the project. A team of dedicated volunteers now follows the breeding success of over 50 nests each year. This hard work has generated a fantastic data set with which to explore how the unusual weather of the Cape Peninsula affects breeding phenology and the role that shifts in breeding phenology has played in the growth of this population.

Raptors3 raptors1

We found that black sparrowhawks on the Cape Peninsula commence breeding up to three months earlier than eastern and north-eastern populations, and that breeding was suppressed during the months of heaviest rainfall. Earlier breeding attempts also produced more chicks. As a result of the shift in timing of breeding, the probability of population extinction was reduced by 23%, suggesting that this phenological shift could have assisted the colonisation of the Cape Peninsula. However contrary to expectations we found no strong evidence that black sparrowhawks were responding to local variation in rainfall within the Peninsula study area. We suggest that shifts in breeding phenology may be driven in part by other novel processes encountered during colonisation, such as interspecific competition for nest sites and lower temperatures during late summer than is the case in the rest of their range.

Raptors4

Clearly there is more to learn about how black sparrowhawks cope with the differing environments they encounter as they have spread westwards. Looking forward, PhD student Gareth Tate is using nest cameras and satellite tracking technology to investigate in further detail how weather influences hunting behavior.

The Authors through Arjun Amar

 

Posted by: oikosasa | June 4, 2014

Editor’s Choice June

DriesPapers published in Oikos should meet the principal criteria to generate synthesis in ecology. Synthesis can be created in different ways and definitively obtained when long-term data sets, novel analytical tools and good hypotheses are merged. The first editor’s choice for the June issue is the paper by Karen Lone and colleagues on multi-predator landscapes of fear. Motivated by challenges to manage large carnivores in Scandinavia in relation to human conflict, the authors used an extensive dataset containing Lidar data, behavioural data and hunting information to demonstrate the interactive impact of multiple predators on predation risk of a single prey species. By means of this integrative approach, the authors demonstrate a predation risk from humans and lynx on roe deer in areas with a high vegetation cover, but an additive impact in more rocky locations. As such, the study demonstrates the complexity of predator-prey interactions in real landscapes, and clearly emphasises the need and value of individual-based ecology to understand interactions in (simplified) foodwebs.

Oikos has decided to highlight meta-analysis papers because of their principal role to create synthesis in ecology.  Chris Lortie will be Editor-in-Chief for this category of papers (look out for his editorial in the August issue). Meta-analysis papers will be published OA for three months after publication. Ward and colleagues tested the performance of time-series forecasting models for natural animal populations based on more than 200 datasets of vertebrate surveys. Such a meta-analysis is considered essential because of the increasing demand to forecast population dynamics under different global change scenarios. While forecasting approaches using non-mechanistic statistical models have greatly evolved the last decades in population biology, still a limited amount of such models are commonly used. By performing a statistical competition experiment, the authors tested the predictive performance of 49 different forecasting models and found simple models to behave well after all, although increasing model complexity fitted time series better in case of species with cyclic population dynamics.

Editor’s choice papers are free online for three months!

The ants underfoot forage faster as the ground warms each day. Likewise, the fish in nearby streams and the worms and other organisms that parasitize these fish speed their activities as the water warms. Above the stream, dragonflies engage in more aerial battles each hour for prime perches as the air warms. We have all witnessed these quickenings, as insects and other ectotherms, organisms whose body temperature are primarily environmentally determined, become more active and interact more quickly in hotter environments. How much faster do such biotic interactions increase with temperature, and why?  This is studied in the Early View paper “Rates of biotic interactions scale predictably with temperature despite variation” by Bill Burnside and co-workers. Their sumary of the study continues here:

Burnside1

Anderson Mancini, Creative Commons – Flickr

 

In this meta-analysis, we look across taxa and habitats to assess the temperature dependence of biotic interaction rates, such as herbivory and competition, between two species. We hypothesize that these rates will increase approximately exponentially with temperature, mirroring the temperature dependence of respiratory metabolism generally. This hypothesis is inspired by the metabolic theory of ecology, which suggests that many ecological patterns and processes are functions of individual metabolic rates of the organisms involved. These rates vary characteristically with body temperature, which affects the rates of cellular chemical reactions. Biotic interactions are metabolic because they involve exchanges of energy and materials between organisms and their environment and because they are inspired by basic metabolic demands, like the need to eat.

Matthew Britton, Creative Commons - Flickr

Matthew Britton, Creative Commons – Flickr

 

This work was intriguing because even though we were not interacting ourselves with all the amazing organisms in our analysis, like those pictured here, we did not know what we would find. The studies were often focused on a related question and just happened to include temperature as a variable or did not include graphs, so it was tough to visualize how some rates varied with temperature. And the rate terms varied by their nature, from the rate ground beetles catch and eat fruit flies to the rate sea lice parasitize fish.

Watershed_Watch, Creative Commons - Flickr

Watershed_Watch, Creative Commons – Flickr

 

Seeing the results for the first time—the generally parallel lines, each with a slope indicating how interaction rate scales with temperature—was amazing. Our results generally supported our hypothesis, but there was also a great deal of variation. We could only find a fairly small sample of studies on most interaction types, which probably accounts for some of this variation, but organisms vary in their level of thermal performance and peak response, among other traits, which surely accounts for variation when different species interact.

Understanding how temperature affects biotic interaction rates is more important than ever in our warming world. The answers won’t be entirely straightforward and may vary among places, species, and communities, but this study offers basic insight to inform our search. 

Vernal pool ecosystems emerge from winter and spring rains that fill shallow depressions in the earth, resulting in small patches of wetlands spread throughout the Central Valley of California, USA. These pools act as a crucial habitat for a diverse community of annual plants, many of which are endemic to the region. Many of these species complete the majority of their entire lifecycle within the short duration that the pool exists. As the standing water evaporates, a stunning array of wildflowers is produced from the plant species that co-occur in these temporary ecosystems. The endemic diversity of these pools, coupled with the short lifespan and small size of the species, makes them an ideal model system for testing questions of community assembly. In the study Functional trait differences and the outcome of community assembly: an experimental test with vernal pool annual plants” in OikosNathan Kraft, Greg Crutsinger, Elisabeth Forrestel and Nancy Emery measured functional trait differences between species in the pools and tested whether these characteristics could be used to predict the outcome of interactions among plant species and, ultimately, the processes structuring the vernal pool communities.

photo 1_smaller

Kraft and colleagues used a greenhouse experiment with eight different annual vernal plant species and grew them together in all pairwise combinations, so that every species had a chance to interact with every other species. They also submerged these combinations in tubs of water for different amounts of time to mimic growing at different depths in a vernal pool. Prior work in this system has found that the recession of water in the spring generates a gradient of species composition along the sides of vernal pools. The authors observed that plant species tended to do better when they had larger leave size, lower specific leaf area (fresh leaf area divided by dry leaf mass), and greater investment in lateral canopy spread than their neighbors. It also turns out that not all individuals within species are equal in these interactions. The authors took an additional step relative to many trait-based studies and measured functional traits for all individuals in the experiment. Models that incorporated individual trait differences did a better job of predicting the outcome of the interactions than models using only species average trait values.

The results of this study suggest that plant traits can be used to help understand the outcome of interspecific interactions in vernal plant communities. It’s also clear that individual trait differences matter. If resources allow, researchers can boost their predictive power by considering trait differences among individuals, instead of focusing on the average traits for different species, which has been the standard practice. There is still more work to be done to understand how vernal pool communities are assembled, as the patterns Kraft and colleagues observed in greenhouse did not strongly match patterns seen in natural pools, suggesting other undiscovered factors are also contributing to species distributions. Ongoing work from Nancy Emery and others will continue to shed light on the processes structuring these fantastic communities in the near future!

Posted by: oikosasa | May 23, 2014

Winter is coming! How do plants react?

How do plants react to seasonal extremes? Find out more in the new Early View paper “Leaf and stem physiological responses to summer and winter extremes of woody species across temperate ecosystems” by Elena Granda and co-workers. Read Elena’s summary of the study here:

Our paper presents evidence that winter stress in the temperate region is more extreme than summer for forests that do not experience summer droughts, but also for those where summer drought combines with winter freezing. In this study we compiled existing literature to identify overall trends of the impact of seasonal extremes on plant performance (leaf and stem physiological responses). We further compared the general patterns over the temperate region with a continental Mediterranean case study subject to intense summer droughts and winter freezing.

Winter

Continental Mediterranean and riparian forests at Alto Tajo Natural Park (Spain) during a) summer drought and b) winter freezing

 Although it is known that winter cold limits plant performance, as is also the case for summer drought in dryland ecosystems, our study revealed that across temperate forests: (i) winter is commonly an equal or even stronger stress than summer, including particular cases of Mediterranean vegetation; (ii) many species are able to maintain stomata open during winter, favoring carbon gain over most of the year; (iii) stomatal conductance and xylem hydraulics show a coordinated seasonal response at sites without summer droughts, and (iv) deciduous angiosperms are the most sensitive to climatic stress.

These results suggest that the differences among functional types in seasonal dynamics of physiological performance are strong enough to advocate their importance in determining ecosystem productivity throughout the year, especially in ecosystems where carbon gain is limited to a few months. These patterns present a baseline against which to compare shifts for key plant species and communities with ongoing climate change.

Posted by: oikosasa | May 20, 2014

How common is bird-pollination in Europe?

Bird pollination in Europe? Really? Well, find out in the Early View paper Flower visitation by birds in Europe” by Luis P da Silva and co-workers. Below is Luis summary of the paper:

Birds are among the most studied animal groups and are most likely the one that attracts more general public attention. These winged animals, are known throughout the world for their interactions and coevolution with plants. They are known to be very important for several plant groups, providing seed dispersal and promoting sexual reproduction through pollination.

When anyone hears about birds pollinating plants, their first thoughts go to hummingbirds, which are very specialized bird pollinators that are able to hover. However, there are other bird groups that are not considered so specialized in pollination (and unable to hover), but well known to pollinate plants, as the honeyeaters. This bird group, somewhat specialized in taking nectar and consequentially pollinate flowers, are present in almost all over the world, except in Antarctica and Europe. If in Antarctica that is not unexpected, in Europe (and actually in almost all the Western Palearctic) that seems a little odd, that how such ubiquitous and abundant food source is not recognized to be regularly exploited by any bird species. With this, insects are often considered the only ecologically relevant pollinators in Europe. Nevertheless, generalist birds are also known to visit flowers and in some cases to successfully pollinate plant species around the world.

Silva

In Europe there are several scattered publish records of flower visitation by birds. We carried out a fine literature search and compiled our own observations to estimate the extent, richness and ecological relevance of this mutualistic interaction. These interactions were not only of direct feeding observation, but also from pollen found attached to feathers, in faeces and stomach contents. We found that 46 bird species visited flowers of at least 95 plant species, 26 of these being exotic to Europe, yielding almost 250 specific interactions inside Europe. Additionally, we registered four more European bird species interacting with 12 different plant species outside Europe. Despite these numbers, only six plants species, both native and exotic, were confirmed to be efficiently pollinated by birds in Europe. We argue that the ecological importance of bird-flower visitation in Europe is still largely unknown, particularly in terms of plant reproductive output. We suggest that nectar and likely pollen are important food resources for several bird species, mainly during winter and spring, especially for tits (mainly Cyanistes), Sylvia and Phylloscopus warblers. The prevalence of bird flower-visitation, and thus potential bird pollination, is slightly more common in the Mediterranean basin, which is a stopover for many migrant bird species, which might actually increase their rule as potential pollinators by promoting long-distance pollen flow. We argue that research on bird pollination in Europe deserves further attention to explore its ecological and evolutionary relevance.

Posted by: oikosasa | May 16, 2014

Who eats the sea urchin?

Different factors that effect predation in marine habitats are explored in the Early View paper Differences in predator composition alter the direction of structure-mediated predation risk in macrophyte communities by Simone Farina and co-worker’s. Below is Simone’s short summary of the study as well as a reflection on the history that lead to the study.

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Using sea urchins as model prey we examined the role of structural complexity in mediating predator-prey interactions across three bioregions: Western Mediterranean Sea, Eastern Indian Oceanand Northern Gulf of Mexico. As expected biomass of the habitat structure and fish predator abundance were the main determinants of predation intensity. Interestingly though, the direction of structure-mediated effects on predation risk was markedly different between habitats and bioregions. In Spain and Florida, where predation by fish was high, structure served as critical prey refuge, particularly for juvenile sea urchins. In contrast in Western Australia predation was generally higher inside the structure where bottom predators were more abundant.

Gallery 1: Meditarrenean Sea

In this sense, as a Mediterranean student I will never forget the days of field work in WA. We had to look for Heliocidaris erythrogramma, the Australian model prey, the equivalent of Paracentrotus lividus in the Mediterranean Sea, and it was like looking for sparrows in the Amazon rainforest. Kelp was full of huge gastropods. Every time I moved a few shoots I had the impression of seeing any kind of tail run away quickly. It was very easy to get distracted from my search. One time we found a huge Coscinasterias calamaria (sea star) remained attached to a fishing line used to mark one of the sea urchins after having swallowed it entire. In seagrass ecosystems (Amphibolis griffithii and Posidonia sinuosa) we observed many little and coloured sea stars (Patiriella brevispina) approaching day by day to our sea urchins and finish them one after the other. In Australian seagrass ecosystems, working to head down supposed some time to have a look around to check for unexpected arrivals of huge sting ray, as ufos flying over a landscape. Macrophyte communities that we explored in Australia are totally different from the Mediterranean ones, so it does not surprise me that structures works in different ways. It was a really pleasure to carry out this experience and I think I’ll have a good story to tell my grandchildren.

Gallery 2: Australia

Posted by: oikosasa | May 13, 2014

How does the habitat effect body size?

By comparing fish communities with bird communities Kirsten Nash an co-workers assess the appropriateness of different size distribution indices used in a variety of studies. The analyses resulted in the Oikos Early View paper Habitat structure and body size distributions: cross-ecosystem comparison for taxa with determinate and indeterminate growth”. Below is the author’s own summary of the paper:

How the study arose:

The study resulted from conversations at the working group ‘Understanding and managing for resilience in the face of global change’, hosted and funded by the USGS Powell Centre for Analysis and Synthesis in Fort Collins, Colorado (https://powellcenter.usgs.gov/). The working group came about through a chance meeting between myself and one of the other authors of our study (Shana Sundstrom) at the 2011 Resilience Conference in Arizona. We were both starting our PhDs addressing similar questions but in different ecosystems: Shana primarily focuses on birds, whereas my research looks at coral reef fish communities. Participants in the working group come from Canada, USA, Sweden, South Africa and Australia.

Nash

Photo of the ‘Managing for resilience’ working group at the USGS Powell Centre in Fort Collins, Colorado:

Description of our group’s focus and short summary of the paper:

An ecosystem can be in a number of different forms or states, such as a reef covered in many corals vs. a reef with large areas of thick algae and little coral. The ability of an ecosystem to remain within its initial form (e.g. coral reef) when impacted by disturbances resulting from rapid global change, rather than shift to another state (e.g. algae reef), is called the resilience of the ecosystem. Until recently, a lot of the work that has looked at the resilience of ecosystems has been theoretical. Our working group focuses on putting this theory into more practical terms, i.e. understanding how likely is it that the ecosystem will remain in its current form over time, as this directly affects natural resources on which we rely for food, water, etc.

 

An important step in this process was to take methods that had initially been developed to look at terrestrial taxa, and explore their appropriateness for marine systems, to ensure that our work was relevant across a range of ecosystems and wasn’t limited to terrestrial studies. The result was our study recently published in Oikos, where we compare the ability of different animal size measurements to highlight the effect of a variety of habitats on the bird and fish communities that live within them. We completed fieldwork on fish communities inhabiting reefs of the Great Barrier Reef and the Seychelles and used published data for bird communities in Borneo (Cleary et al., 2007, Ecological Applications) and the Lofty Ranges, Australia (courtesy of Hugh Possingham and the Nature Conservation Society of South Australia). The study shows that both average and individual size measurements are useful for showing the effect of habitat on bird communities. In contrast, for fishes, we need to incorporate the size measurements of all individuals within a community to show the effects of habitat on fishes.

 

 

Posted by: chrislortie | May 12, 2014

Sharing data issues for ecology and evolution

An open future for ecological and evolutionary data?
Amye Kenall*, Simon Harold and Christopher Foote
doi:10.1186/1472-6785-14-10

A very succinct and accurate editorial on the future directions needed for data sharing in ecology & evolution was recently published at BMC Ecology. The key issues for ecology & evolution were identified and included the following:

Opportunity cost: available data reduces costs, provides opportunities, and serves local stakeholders

Shared benefits: new forms of collaboration, discovery, and accelerated synthesis will emerge

Blood, sweat and tears: long-term datasets are hard won and it is difficult to let them go (public)

A bigger picture: macroecology and other relatively new ways of doing ecology need open data

Data management: metadata is critical, always, and for ecology/evolution in particular because the ‘lab’ is often outdoors

Credit where credit is due: many new reputation economy tools and reward systems are in place to serve as incentives for all scholars not just for ecology and evolution

Transparency and trust: we review the manuscripts of others, why should datasets be free from scrutiny?

Each issue is well described. The one that clicked the most for me was the ‘blood, sweat, and tears’ argument as I have heard it made by many ecologists. Fieldwork can be grueling.  We also hope that we will reuse our own datasets many times. However, I suspect that we do not. Let them go free. As a personal goal, I have mentioned the idea of #ecodataweek on twitter as a good push to myself via a bit of friendly competition to get stuff out there more too.

Oikos also partners with Dryad, and I hope that this editorial likewise inspires you to publish your data.  I would also love to see a more in-depth set of analyses for Oikos readers on these topics and how they relate to the journal mission of ‘novel synthesis’ and synthesis science in general.

Additional resources to consider:
1. DataONE for data management planning tools and a list of best management practices for data documentation (pdf link is best).
2. A good read on how our discipline has likely crossed into the realm of big data.
3. The pivotal nature of data sharing to the future of publishing in ecology.
4. Re-read the file-drawer problem papers such as the Csada et al. 1996 Oikos paper on the topic (classic for ecology but still feels modern with issues of limited OA and accessible data).

 

data_01

 

 

Posted by: oikosasa | May 9, 2014

Linking theory with empirical studies of competition

“Nature is much more complicated” than predicted in theoretical  models. In the Early View Paper “Matrix models for quantifying competitive intransitivity from species abundance data”, Werner Ulrich and colleagues try to fill a gap between models and mother nature when it comes to competition interactions.

Below is their summary of the study:

Ecologists have devoted much effort to inferring competitive processes from observed patterns of species abundances, morphology, and particularly from changes in the spatio-temporal distribution, (i.e. species co-occurrences). Classic assembly rules models, derived from the principle of competitive exclusion, predict that differences in competitive abilities should cause non-random patterns of species occurrences among sites and generate inequalities in species abundances within sites. Competitively inferior species are predicted to occur less frequently and at lower abundance, and an important and largely unresolved question is how such species can persist in a community over long time periods (also known as Darwin’s paradox and nicely explained in http://www.wbez.org/blog/clever-apes/2011-11-22/clever-apes-22-paper-covers-rock-94295) .

Simple competition models assume that species can be ranked unequivocally (A>B>C…>Z) according to their competitive strength. However, nature is much more complicated and intransitive competitive networks can generate loops in the competitive hierarchy (e.g. the rock-scissors-paper game, in which A>B>C>A). Importantly, such loops allow weak competitors to coexist with strong ones. Additionally, the structure of such loops might be modulated by environmental factors. Experimentally competitive strength can be tested with simple two-species systems. Testing competitive interactions in many-species systems requires an increasing number of species exclusion experiments.

Bild1

Up to now no comprehensive theoretical framework existed to infer competitive loops from observed patterns of species abundances. Existing mathematical models based on presences and absences of species (on perfect competitive exclusion) have rarely been applied to empirical data. Our new paper in Oikos seeks to fill this gap in our knowledge. We introduce a statistical framework for evaluating the contribution of intransitivity to community structure using species abundance matrices that are commonly generated from replicated sampling of species assemblages. We use a stochastic back-engineering procedure to find a transition probability matrix that predicts best observed distributions of abundances in an ordinary Markov chain approach. We then use a probabilistic argument to convert this transition matrix into a pairwise competition matrix that contains the information of competitive strength between all species in the community. Our approach can be used for abundance data, time series, and abundances in combination with environmental data. Our case study on necrophagous flies and their hymenopteran parasitoids revealed strong hints towards instable competitive hierarchies. In other words the competitive outcome in these communities (having at least five species) strongly depended on environmental conditions but also on the spatial structure of fly and parasitoid occurrence.

Bild2

We hope that our new approach sparks a fresh new look at competitive interactions in ecological communities and helps to assess and appreciate the importance of intransitivity for the coexistence of species in natural communities. We fell the need for joint approaches that link existing methods using the temporal and spatial co-variation in species abundances and occurrences with methods (like our) that reconstruct competitive hierarchies. 

Posted by: oikosasa | May 7, 2014

Mixture models instead of bimodality?

Bimodality – the characteristic of a continuous variable having two distinct modes – is of widespread interest in data analysis. This is because, in some cases, we can use the presence or absence of bimodality to infer something about the underlying processes generating the distribution of a variable that we are interested in studying. In ecology, tests of bimodality have been used in many different contexts, such as to understand body size distributions, functional traits, and transitions among different ecosystem states. But a lack of evidence for bimodality has been reported in many studies. Our paper “Masting, mixtures and modes: are two models better than one?”, now shows that a widely-used statistical test of bimodality can fail to reject the null hypothesis that focal probability distributions are unimodal. We instead promote the use of mixture models as a theory oriented framework for testing hypotheses of bimodality.

Our interest in this problem arose with the publication of Allen et al. 2012 Oikos 121: 367–376. The paper impressive synthesised 43 years of seeding patterns in a New Zealand mountain beech Nothofagus forest. Seed production in these trees is interesting because a population can go several years without reproducing and then all the individuals in a population will do so. Such intermittent and synchronous reproduction is also known as mast seeding.

 

Dense Nothofagus forests (dark green) dominate mountain-sides in Fiordland, New Zealand

Dense Nothofagus forests (dark green) dominate mountain-sides in Fiordland, New Zealand

 

In their paper, Allen et al. tried to infer the importance of resource limitation in driving mast seeding patterns by describing various characteristics of seed production. A key finding was that they could not reject the null hypothesis that the distribution of annual seed production was unimodal using an empirical calculation known as Hartigan’s dip test. Allen et al. 2012 concluded that few studies could ‘robustly test for bimodality’ because they lacked ‘long time-series’ and used questionable methods.

Bimodal5

 

Nothofagus solandri var. cliffortioides trees in Fiordland, New Zealand

The bimodality result inspired a lot of reflection. We were interested in why we might consider an annual count that takes values larger than zero at more than 2 year intervals to ever even present two modes. Populations should only have one mode because the single most frequently observed seed count will be relatively low, on average, in most years. Thus, plants can never be bimodal when a single distribution is fit to seed counts – even if they alternate annually, on average, between the absence and presence of seed production. This is because of the underlying statistical nature of seed counts, which we describe in further detail in our paper.

Stepping back further from the problem, we began to realize that there is a need to consider multiple probability models, each with at least one unique mode, where plants flower at >2 year intervals.We illustrate these ideas by analysing 37 years of data from five grass species in New Zealand. Critically, we found clear evidence for bimodality using mixture models that associate distinct probability distributions with medium- and high- versus non- and low-flowering years. We expect these patterns to be driven by different processes and hence, modelled by different probability distributions. We found no evidence for bimodality with Hartigan’s dip test that assumes a single probability distribution can be fitted to all the data. Our findings show the importance of coupling theoretical expectations with the appropriate statistical tools when predicting the responses of ecological processes.

 

Bimodal4

Snow tussock Chionochloa rigida flowering in Fiordland, New Zealand

The authors through Andrew J. Tanentzap

Posted by: oikosasa | May 3, 2014

Fever, starvation or being eaten?

Talk about choosing between pest and cholera! A bird on migration, has a tough job, and with a virus infection in the body, the job is even worse! In the early View paper “A tradeoff between perceived predation risk and energy conservation revealed by an immune challenge experiment”, by Andreas Nord and co-workers.

Below is Andreas summary of the study:

Birds, like man, must maintain a high and even body temperature to function properly. This is a challenging task, not least in winter when the internal temperature may be some 50-60 °C above that of the surroundings. It is not surprising that this challenge requires high food intake. In fact, a blue tit, which is a common garden and forest bird across Europe, must sometimes put on 10 % of their body weight as fat on a daily basis during cold winter days. A human of average weight would have to eat some 200 hamburgers to ingest the same amount of fat.
Nord1
As if this was not enough, the time of peak food demand often coincides with the time when food resources are the most difficult to obtain. To overcome such hardships, many animals actively reduce their body temperature at night (nocturnal hypothermia), a process that substantially lowers their energy demands. Yet the use of nocturnal hypothermia is often not enough to avoid the risk of starvation, because the demands from other body functions compete for the same fat reserves. In these situations, birds may have to prioritize surviving the night by reducing the use of other costly functions, such as the immune defense system. In other words, because food availability is limited in winter, it may not be possible to maintain sufficient amounts of body fat at the same time as an adequate defense against invading pathogens.
Nord3
This was the subject for our study, in which we investigated how an activated immune defense system impacted on the use of nocturnal hypothermia and behavioral strategies for minimizing energy expenditure in wild blue tits in southern Sweden. Contrary to our expectations, an immune response did not cause birds to change their use of nocturnal hypothermia, which could indicate that any energy costs of the immune defense system are not large enough to interfere with energy conservation processes. However, birds with an ongoing immune response showed a different behavior compared to healthy birds, which was manifested as an increased use of sheltered roosting sites when the immune response was at its peak. Using such roosting sites often confers energy savings, because birds are less exposed to wind and temperatures are higher than those outside. However, sheltered roosts often come at the expense of increased predation risk, because these roosts may be easier to locate and escape prospects are typically relatively low upon detection.
Nord4
We interpret this increased risk taking behavior in sick birds as consequences of a higher need to exploit the energetic benefits of sheltered roosts. Because this required birds to accept a higher predation risk at night, our results may indicate that energy stress from less efficient thermo-regulation poses a higher mortality risk for sick birds than does any predation risks pertaining to sheltered roosting sites. This was not the case for healthy birds, whose thermo-regulatory capacity was not impaired by an ongoing immune response. These birds instead actively avoided sheltered roosts, because their main source of overnight mortality might indeed have been the risk of predation.
Posted by: oikosasa | April 29, 2014

Dispersal and endoparasites in roe deer

Natal dispersal is a complex process but what could be the role of endo-intestinal parasites in dispersal propensity, distance and date of departure? In our article “Parasite abundance contributes to condition-dependent dispersal in a wild population of large herbivore” we look at this question on a roe deer population inhabiting a fragmented and anthropogenic landscape in South-West France.

Parasite abundance has been shown to have major consequences for host fitness components such as survival and reproduction. However, although natal dispersal is a key life history trait, whether an individual’s decision to disperse or not is influenced by the abundance of parasites it carries remains mostly unknown. Current and opposing hypotheses suggest that infected individuals should either be philopatric to avoid the energetic costs of dispersal (condition dependence) or disperse to escape from heavily parasitised habitats.

Roedeer1

Our study site hilly and fragmented in the “coteaux de Gascogne” in South-West France.

 

Roe deer were capture during winter, we sample fresh faeces and we collared them with a GPS collared in order to follow their movement during approximately one year before to release them in site. Their natal dispersal behaviour could thus be evaluated with accuracy.

 

Collection of faeces sample during marking

Collection of faeces sample during marking

 


Roedeer3aRoedeer3b

Roedeer3c

Back to the field with a beautiful GPS collar

Our results show that dispersal propensity generally decreased with both increasing nematode abundance and with decreasing body mass. Within the dispersing segment of the population, individuals with high nematode abundance left their natal home range later in the season than less parasitised deer. These results clearly show that parasite abundance is an important component of condition-dependent dispersal in large herbivores. However, unexpectedly, three individuals that were both heavily parasitised and of low body mass dispersed. We suggest that this “leave it” response to high parasite levels in the natal habitat could represent a last ditch attempt to improve reproductive prospects, constituting a form of emergency life history strategy.

The authors through Lucie Debeffe who also took the photos

Posted by: oikosasa | April 23, 2014

Geographic variation in bird survival

How life-history traits vary across longitude is studied in birds in the Amazonas in the Early View article “Variation in tropical bird survival across longitudes and guilds: a case study of the Amazone” by Jared D Wolfe and co-workers. Below is Jared’s summary of the paper:

Jared Wolfe with Wing-banded Antbird in the central Amazon

Measuring the annual survival of birds, or the probability of a bird living from year-to-year, has fueled theory regarding life history strategy in temperate and tropical birds. For example, because tropical birds have fewer young over the course of a year relative to their northerly counterparts, scientists have often expected tropical birds to exhibit higher survival than temperate birds as part of a ‘trade-off’ in life-history strategy. In our paper we examined variation in annual survival among birds across the Amazon. We used a decade of bird capture data from the central Amazon to estimate the annual survival of 31 bird species and compared our results with those from western and eastern Amazonian forests.

Jared Wolfe banding a Wing-banded Antbird at the study site in the central Amazon - 2nd picture

We also examined differences in annual survival between bird species that differ in mass, foraging and nesting behavior at our study site in the central Amazon. In general, community-wide annual survival was remarkably similar across the Amazon, but several species did exhibit dramatic differences in survival estimates. The most striking variation in estimates of survival was exhibited by the White-plumed Antbird (Pithys albifrons), for which survival estimates were nearly twice as high in eastern than the western Amazon, but intermediate in the central Amazon. We also found that nest architecture moderately influenced annual survival of birds at our study site in the central Amazon. Our results suggest that geographic variation in survival may be significant for widespread Amazonian species.

white-plumed Antbird from the central Amazon - photo by Angelica Hernandez Palma

Posted by: oikosasa | April 22, 2014

Herbivory, competition and global warming

How altered temperature might affect competition and herbivory in plant communities is studied in the early View paper “Concurrent biotic interactions influence plant performance at their altitudinal distribution margins” by Elina Kaarlejärvi and Johan Olsson. below is their summary of the paper:

The idea behind this paper was to test whether herbivory and competition influence growth and reproduction of lowland and tundra forbs at different altitudes. Previous studies had indicated that these biotic interactions could play a role in determining species altitudinal distributions, but this has been rarely experimentally tested.   We studied this in subarctic Abisko, in northern Sweden, on meadow habitats at two altitudes, at 600 and 900 m a.s.l. We selected five study sites at the two altitudes, each of them consisting of a pair of plots: one plot was fenced against large mammalian herbivores, while another was left open. Nested within this herbivore exclusion treatment we carried out biomass removal treatment to investigate effect of plant-plant interactions. We planted seedlings of lowland and tundra species to both altitudes and followed their growth and reproduction over two growing seasons.

Studying plant-plant interactions. Planting seedlings of lowland and tundra forbs to a subplot without neighboring vegetation at a low altitude site.

Studying plant-plant interactions. Planting seedlings of lowland and tundra forbs to a subplot without neighboring vegetation at a low altitude site.

 

A fence against large mammalian herbivores in a study plot at a high altitude site. Early summer visit to the study sites to record signs of winter herbivory and check the condition of the fences.

A fence against large mammalian herbivores in a study plot at a high altitude site. Early summer visit to the study sites to record signs of winter herbivory and check the condition of the fences.

We had expected to find competition at low altitudes and facilitation at high altitudes, but found that competition prevailed in both altitudes. However, high-altitude tundra forbs suffered more from competition; neighbor removal increased the proportion of flowering individuals and tended to increase growth of one of the high-altitude species more at low altitudes. Since the low altitude sites were about 2°C warmer (summer air temperatures) than high altitude sites, these results suggest that climate warming may strengthen competition and potentially shift lower distribution margins of high-altitude forbs upward. Interestingly, mammalian herbivores may counteract these climate-driven distribution shifts, as they reduced the growth of lowland forbs and enhanced the flowering of tundra forbs.

Posted by: oikosasa | April 15, 2014

Climate effects on plant chemistry

Lots of traits are climate dependent! In the Early View paper in Oikos Genetically based latitudinal variation in Artemisia californica secondary chemistry” by Jessica Pratt and co-workers, terpenes are studied under different climatic situations.Below is a summary of the paper: 

Gradients in environmental conditions can serve as a ‘space for time’ substitution when trying to understand how species might respond to current and future environmental change and have thus become the focus of much recent work. Environmental gradients and gradients in biotic interactions often result in corresponding gradients in plant traits within a species. In our study, we examined variation in leaf terpene chemistry for the foundation species California Sagebrush (Artemisia californica) in Coastal Sage Scrub habitat across a 700 km latitudinal gradient in California. This gradient is characterized from south to north by a four-fold increase in precipitation.

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

We collected California Sagebrush from five source populations distributed across this gradient and grew them in one common environment where we manipulated precipitation. Such common environment studies, when done in conjunction with environmental manipulations, provide a powerful approach to pinpoint the underlying causes of variation in plant traits and determine how such variation relates to large-scale ecological variation.

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

Coastal Sage Scrub community in the Santa Monica Mountains with Californica Sagebrush in foreground

Pratt_sagebrush

Terpenes – one of the most diverse groups of plant secondary compounds – are important in providing defense against herbivores and also play several additional roles in the community. They are involved in plant-plant communication, drought and thermal tolerance, and adaptation to fire, and can influence plant relationships with other plants, animals, and microorganisms. We tested for genetically based variation in leaf terpene richness, diversity, concentration, and composition and examined whether precipitation was a key selective force on terpene chemistry.

California Sagebrush experimental garden plot

California Sagebrush experimental garden plot

Our results showed that California Sagebrush source populations differed in terpene richness, diversity, concentration, and composition, with terpene composition and concentration varying clinally along the gradient. Plants from source populations that were closer together geographically had a more similar composition of terpenes than those farther apart, and terpene concentration decreased clinally from south to north. Our manipulation of precipitation suggests that selection for lower terpenes under increased precipitation may underlie this clinal pattern that we observed. Interestingly, we did not see a direct influence of the precipitation manipulation on terpene chemistry indicating these traits may not be phenotypically plastic in response to altered precipitation.

Pratt_sagebrush

We conclude that changes in terpene chemistry under projected future climates will likely occur only through the relatively slow process of adaptation, and this will have important consequences for California Sagebrush’s interactions with the environment and a diverse community of associated species.

Posted by: oikosasa | April 11, 2014

Haiku on risky dispersal

Have you ever tried to summarize your research in a poem? This haiku summarizes the Early View paper “Population-level consequences of risky dispersal”, by Allison K. Shaw and coworkers.

risky dispersal
whether too much, too little
both suboptimal

to selfishly leave
more or less than the others
may just hurt us all 

Oceans, they scare me
Nearby islands, too, stay far
I prefer it so.

Below, is a more traditional popular summary of the paper:

All living organisms move (disperse) at some point during their life. Many plants produce seeds that disperse away, and the offspring of most animals eventually grow up and move away from their parents. Moving has benefits as well as costs. By moving, an individual can find better food resources, or potential mates. However, by moving an individual also leaves behind familiar areas and faces the risk of possibly never finding a place to settle, or even dying along the way. So for each individual, there is some ‘best’ amount of movement: not too much and not too little.

However, moving individuals can also influence the population they live in: movement determines how spread out the population is across a habitat, and how much movement there is between different areas of the habitat. Therefore, from the perspective of the population, there is also a ‘best’ amount of dispersal. If individuals are spread out across the habitat, this can allow the population to reach a larger size, which increases the probability that the population will persist over time.

The question we ask in this paper is: what is the relationship between the amount of dispersal that is ‘best’ for an individual and the amount that is ‘best’ for the population? If they are not the same, which one is bigger and why?

To answer this question, we built a model (see Figure). We find that generally (1) when the area a population occupies is small, (2) where the habitat can only support a few individuals and (3) when there is a high risk of dying during dispersal, the amount of dispersal ‘best’ for an individual is smaller than the amount ‘best’ for the population. In these cases, the population size would increase if only individuals dispersed more. This suggests that as a conservation strategy for endangered species, restoring habitat may not be enough but may need to be combined with some form of assisted movement.

 

 

Dispersal

A schematic of our model. Individuals live in a habitat area of limited size, made up of smaller patches. If individuals disperse (leave the patch where they were born) they can either land successfully in another patch, die during dispersal, or die if they move beyond the habitat edge.

 

 

 

 

Posted by: oikosasa | April 8, 2014

Apex predators on coral reefs

Apex predators are large carnivores that occupy the top trophic level of food webs. Globally, apex predators are assailed by disturbances such as persecution by humans. This is worrisome because changes in the density and distribution of apex predators can exert strong direct and indirect ecological effects that cascade through an entire ecosystem. However, our knowledge of these indirect ecological effects is still limited, particularly in marine environments. Coral reefs are one of the most diverse ecosystems, providing a useful model system for investigating the ecological role of apex predators and their indirect influence on lower trophic levels. In our work “Not worth the risk: apex predators suppress herbivory on coral reefs”, conducted on Lizard Island in the Great Barrier Reef (Fig. 1), we examined the indirect effects of two species of apex predators, a reef shark and large-bodied coral-grouper, on herbivore foraging we behaviour.

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Figure 1. Location of study site

Using a novel approach of mimic predator models (Fig. 2) and GoPro video cameras we show that in the presence of an apex predator there is an almost localized cessation of algae consumption, due to the perceived risk of predation. Our work suggests that the indirect behavioural effects of apex predators on the foraging behaviour of herbivores may have flow-on effects on the functioning of coral reef ecosystems. This highlights that the ecological interactions and processes that contribute to ecosystem resilience may be more complex than previously understood.

 

Figure 2. Apex predator models. (a) Blacktip reef shark, (b) large coral-grouper and (c) small coral-grouper.

Figure 2. Apex predator models. (a) Blacktip reef shark, (b) large coral-grouper and (c) small coral-grouper.

Picture below is of lead author Justin R. Rizzari (website: http://www.coralcoe.org.au/students/justin-rizzari)

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Posted by: oikosasa | April 4, 2014

Severe geographic bias in pollination studies

The majority of pollination studies are performed in five countries, non of which in Africa. How does this bias affect application of the research in various geographic regions? Find out in the Forum paper in the April Issue of Oikos “Economic and ecological implications of geographic bias in pollinator ecology in the light of pollinator declines” by Ruth Archer and co-workers. Below is their summary of the paper:

Across much of the world pollinator loss has captured the attention of the media and the public.  In Europe pollinators regularly feature on the front page but here in southern Africa pollinator losses have received much less attention.  This doubtless reflects an underlying problem: in Africa, as across much of the world, we lack the data to record changing populations of pollinators or identify the threats facing them. 

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In our opinion piece we aim to highlight that current understanding of pollinator losses (and more generally pollinator ecology) is based on data of comparatively narrow geographic scope.  More specifically, we show that almost half the data cited in thirteen recent meta-analyses, which ask important and diverse questions in pollination ecology, were collected in just five countries and Africa contributed only 4% of the data.  Does this matter?  Perhaps not, if the threats facing pollinators and responses to these challenges are similar across different regions, habitats and pollinator species.  However, this is unlikely.  There is enormous geographic variation in the distribution of anthropogenic disturbances, pests and parasites that are likely to impact negatively on pollinators.  For example, the Varroa mite, which is a major problem for European and North American honeybees, has less serious effects in subsaharan Africa and has not yet arrived in Australia.  Also, much more natural habitat remains in Africa than in Europe or America, although the speed of land use change is probably higher in Africa.  As pressures vary geographically, so too are different pollinators likely to vary in responses to them.  For example, subspecies of Apis mellifera differ in a suite of physiological and behavioural traits that make it unlikely that they will respond to ecological changes in the same way; therefore, management strategies designed around data collected on European honeybees may not be applicable to African subspecies.  Finally, from a socioeconomic perspective we need to better understand plant-pollinator interactions in understudied regions where the loss of pollination services could have immediate, dire effects: for example, where communities rely on subsistence farming or beekeeping for food security. 

If there are geographic gaps in our understanding of pollinator ecology and if these matter, what can we do about the issue given the socio-economic and logistical constraints that are likely responsible for much of this geographic bias?  In our article we offer solutions but, more importantly, hope to stimulate discussion on this important issue.  

Posted by: oikosasa | April 1, 2014

Metapopulation modeling of endangered rabbits

Can hard-to-detect individuals of an endangered and declining population allow for testing of some of the major tenets of metapopulation theory while contributing to conservation efforts? A new multi-season occupancy model combined with observations on the Lower Keys marsh rabbit may have done just that. Read the Early View paper “Testing metapopulation concepts: effects of patch characteristics and neighborhood occupancy on the dynamics of an endangered lagomorph” by Mitchell J. Eaton and co-workers. below is their summary of the paper:

The Lower Keys marsh rabbit (LKMR, Sylvilagus palustris hefneri) is an endemic species found only on a handful of islands in the lower Florida Key islands. Following decades of decline caused by habitat fragmentation and degradation, sea-level rise and high rates of mortality inflicted by non-native predators, the LKMR was listed as endangered under the U.S. Endangered Species Act in 1990. Although several of these contributors to population decline have been improved, the distribution of the marsh rabbit continues to fall. With limited dispersal abilities, this secretive species persists in isolated habitat patches found within a highly fragmented landscape, challenging managers to identify viable solutions for their conservation and recovery. Given these conditions, a better understanding of the spatial aspects of marsh rabbit population dynamics could provide important insights and contribute to management efforts. We believed that a metapopulation framework would be the most useful for describing these dynamics. We were concerned, however, that existing metapopulation models were more theoretical than practical, based on too many assumptions and insufficient for dealing with the realities of a rare and hard-to-detect species. Therefore, we developed a new, flexible multi-season occupancy model that could test the concepts and assumptions of metapopulation theory, while investigating the dynamics of this species for the ultimate purpose of making recommendations for species management and recovery.

 Since its introduction in the 1960s, and following years of model development and application to natural systems, the theoretical underpinnings of metapopulation ecology have been strongly tied to assumptions about the relationship between neighboring patches, non-habitat (‘matrix’) characteristics and the probabilities of focal-patch extinction and colonization. Much recent work in metapopulation ecology has focused on developing advanced models that allow for incorporation of more detailed biological information to explain patterns in patch dynamics. Many of these models, however, have not taken into account the realities of imperfect detection in field sampling. As a result, only incomplete information on the abundance or occupancy levels of the surrounding landscape is available when making inference on the dynamics of a focal patch. As such, metapopulation models often rely on neighboring patch characteristics (e.g., perceived quality or size) as a proxy for the existence or abundance of colonizers and assume that local colonization will increase with patch connectivity. Local extinction probability has traditionally been modeled as a function of patch size, but is also predicted to be influenced by connectivity with neighboring habitat via a ‘rescue effect’. This latter process similarly depends on assumptions about the relationship between measurable patch characteristics and neighborhood occupancy, which can be difficult to quantify without consideration of the possibilities of non-detection.

 Building on recent advancements of the use of so-called ‘autologistic’ covariate models, we have developed a new multi-season occupancy model to explicitly incorporate estimates of neighborhood occupancy when modeling the dynamics of a metapopulation. Rather than treating the status or condition of a neighboring patch as certain (i.e., as a traditional, known covariate) we consider the occupancy of neighboring patches as an unobservable variable to be estimated. Our flexible model specification allows the ‘neighborhood’ to be defined in any number of ways, permitting nearly any a priori biological hypothesis to be tested. The model allows inclusion of a gradation of neighboring patch influence on the focal patch (e.g., habitat quality, distance, etc.) using patch-specific weights, as well as the quantification of non-habitat (e.g., water bodies) within the neighborhood. Using this modeling approach, we recast many of the assumptions of metapopulation theory as hypotheses to be tested explicitly.

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Our results supported two of the major assumptions of metapopulation theory, namely that colonization probability is positively related to the occupancy of neighboring patches and that extinction probability is negatively related to local patch size. We also found support for the rescue effect, with extinction being mitigated by higher neighborhood occupancy, and for higher colonization rates being related to larger patch size. Model selection suggested that LKMR focal patch dynamics were influenced by a neighborhood effect size of approximately 1000m. Model results also suggest that patches in coastal areas (believed to be of higher quality for the species) experienced higher turnover rates than inland patches and that disturbance from sea-level rise, storm frequency and vegetation dynamics may be further destabilizing coastal patches. We found that lower-quality inland patches, which appear to be experiencing slower species turnover dynamics, may serve as refugia and provide an important source for colonization of coastal patches following local extinctions. Our findings can help managers better understand optimal spatial habitat configuration when planning restoration activities, predicted impacts of patch-specific removal of non-native predators and where translocations of LKMR would be most effective.

 

Posted by: oikosasa | March 28, 2014

Meta-community structure in rodent parasites

What are the roles of host phylogeny, transmission variables, and host traits in molding parasite metacommunity structure? Find out in the new Early View paper “Relative importance of host environment, transmission potential and host phylogeny to the structure of parasite metacommunities” by Ted Dallas and Steven J Presley. Here’s their own summary of the paper:

Identification of mechanisms that shape parasite community and metacommunity structures have important implications to host health,disease transmission,and the understanding of community assembly in general. In addition, a metacommunity approach can enhance the understanding of parasitological relationships among hosts, which may be reservoirs for emerging diseases or act as vectors that transmit diseases to humans or agriculturally important domestic animals.

 A metacommunity is typically defined as a set of ecological communities forming a network in space, such as  fish communities from a series of lakes across a landscape. However, Mihaljevic (2012) recently argued that metacommunity theory could be used to better understand parasite ecology. In our study, we considered host species to represent sites, with each host species harboring a distinct community of parasites. Each host species has a unique set of traits that define the environment for the parasites, the likelihood of parasite transmission to other host species, and the co-evolutionary relationships between hosts and their parasites.

 

 

Dallas 

Figure 1: Parasite distributions among rodent host species. Parasite group identity is indicated by color of the text in the graphic below the figure (e.g. Coccidians are in green).

 

We used data on rodent parasites from the Sevilleta Long Term Ecological Research Study to investigate parasite metacommunity structure from two perspectives. First, we used the Elements of Metacommunity Structure (EMS) framework to determine if parasite species distributions among hosts formed coherent structures (Leibold and Mikkelson 2002). Second, we assessed the relative roles of host phylogeny, host traits that can affect parasite transmission (e.g. home range size, diet breadth), and host traits that define the environment (e.g. body size, trophic status, longevity), using a variance partitioning analysis.

 Three distinct metacommunity structured occurred, Clementsian, quasi-Clementsian, and random. Despite the variation in structure,  host environment explained the largest proportion of the variation in community structure (~30%). This highlights the fact that no a priori relationship exists between particular structuring mechanisms and particular metacommunity structures. This suite of distinct responses from the same host metacommunity highlight the complex and diverse nature of host-parasite systems with respect to how parasites move through the environment, variation in life histories, and level of host specialization they exhibit. Mechanisms that contribute to parasite metacommunity structure may be highly complex, as host metacommunities can exhibit complex responses to local and spatial processes, with responses of hosts to large-scale environmental variation and responses of parasites to variation in host characteristics all contributing to parasite metacommunity dynamics.

 

Leibold, M. and Mikkelson, G. 2002. Coherence, species turnover, and boundary clumping: elements of meta-community structure. – Oikos 97: 237–250.

Mihaljevic, JR. Linking metacommunity theory and symbiont evolutionary ecology. Trends in Ecology & Evolution.

Posted by: oikosasa | March 27, 2014

Effects of small mammal outbreaks in the Serengeti

After more than 50 years of research into the ecology of large herbivores and predators in the greater Serengeti ecosystem, you might think that we know almost everything there is to know about this tropical savanna ecosystem. But in our article, Episodic outbreaks of small mammals influence predator community dynamics in an East African savanna ecosystem (Andrea E. Byrom et al.), we show that relatively little attention has focused on the role of small mammals (rodents and shrews) in tropical African savannas such as the Serengeti. This presents a critical gap in our understanding of one of Africa’s best known ecosystems.

Tropical savanna woodland, Serengeti National Park

Tropical savanna woodland, Serengeti National Park

We do know that in agricultural areas throughout East Africa, rodent populations fluctuate (outbreak) with large peaks in abundance, triggered by increased food availability during the dry season in response to the amount of rain in the preceding wet season. When outbreaks occur, species such as the multimammate rat Mastomys natalensis and the African grass rat Arvicanthis niloticus cause substantial economic damage in crop-growing areas. Before our study, however, little was known about the population dynamics of small mammals in tropical savanna, or their trophic importance, including as prey for some threatened carnivore species. Small mammals are a known food source for predators in this system, including mammalian carnivores in the weight range 1–18 kg, and birds of prey.

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Arvicanthus niloticus, the African grass rat

It’s not surprising that researchers travel from all over the world to study an ecosystem as diverse and well-known as the Serengeti. Our team comprised researchers from Tanzania, New Zealand, Australia, the USA, Canada, and the UK – all scientists who had lived or worked in East Africa. Some of us have never met, but we all contributed to collection of the data that were used in this article. We pieced together a 42-year time series (1968-2010) on the abundance of 37 species of small mammals, derived from intermittent measures collected in Serengeti National Park and adjacent agricultural areas. Data on abundance of black-shouldered kites (1968–2010), eight other species of rodent-eating birds (1997–2010), and 10 mammalian carnivore species (1993–2010) were also collated.

Black-chested snake eagle, Circaetus pectoralis

Black-chested snake eagle, Circaetus pectoralis

We used climatic fluctuations and differences between unmodified and agricultural systems as perturbations to examine both bottom-up and top-down drivers of small mammal abundance: key to understanding responses to climate change and increasing human pressures adjacent to Serengeti National Park. Outbreaks occurred every 3–5 years in Serengeti National Park, with low or zero abundance of small mammals between peaks. There was a positive relationship between rainfall in the wet season and (a) small mammal abundance and (b) the probability of an outbreak, both of which increased with negative Southern Oscillation Index values. Rodent-eating birds and carnivores peaked 6–12 months after small mammals. In agricultural areas, abundance remained higher than in natural habitats.

 

The serval, Leptailurus serval

The serval, Leptailurus serval

We conclude that small mammal outbreaks have strong cascading effects on predators in African savanna ecosystems. Changes in climate and land use may alter their future dynamics, with consequences for higher trophic levels, including threatened carnivores. Although outbreaks cause substantial damage to crops in agricultural areas, small mammals also play a vital role in maintaining some of the diversity and complexity found in African savanna ecosystems. Our study provides vital baseline data from which to monitor the future resilience of tropical savanna ecosystems.

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Posted by: oikosasa | March 25, 2014

Life hots up for long-tailed tits

The winner of the Global warming is – The long-tailed tit! Read more in the Early View paper “Climate change and annual survival in a temperate passerine: partitioning seasonal effects and predicting future patterns” by Philippa Gullet and colleagues. below is the press release, that at least have reached BBC News!

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Climate change may be bad news for billions, but scientists at the University of Sheffield have discovered one unlikely winner – a tiny British bird, the long-tailed tit.

Like other small animals that live for only two or three years, these birds had until now been thought to die in large numbers during cold winters. New research published this week suggests that in recent years, weather during spring instead holds the key.

The findings come from a 20-year study of long-tailed tits run by Prof. Ben Hatchwell at the Department of Animal and Plant Sciences. The recent work is led by PhD student Philippa Gullett and Dr. Karl Evans from Sheffield, in collaboration with Rob Robinson from the British Trust for Ornithology.

“During spring, birds must work their socks off to raise their chicks,” said Philippa Gullett.

“For most small birds that live for only two or three years, not raising any chicks one year is a disaster. They might only get one more chance, so they can’t afford to fail.”

No surprise then that these birds are willing to invest everything and risk death if it means their young survive. The surprise is that weather makes all the difference. The research discovered that birds trying to breed in warm and dry springs have much better chances of surviving to the next year – a novel result that counters common assumptions about the cause of death for small birds.

“What seems to be going on is that the tits try to raise their chicks at any cost”, added Ms Gullett. “If it’s cold and wet in spring, that makes their job much tougher. Food is harder to find; eggs and chicks are at risk of getting cold. The result is that by the end of the breeding season, the adult birds are exhausted.”

The Sheffield team also found that despite no real effect of winter weather in recent years on adult survival, cold and wet autumns were associated with a higher death rate.

“We’re not saying that birds never die in winter – in harsh years there are bound to be some fatalities,” explains Dr. Karl Evans, supervising the research.

“However, it seems that in most years autumn weather plays a bigger role, perhaps acting as a filter that weeds out weaker birds before the real winter hits.”

Although autumns may get wetter in the coming years, any increase in mortality is likely to be offset by the benefits of warmer breeding seasons, when more benign

conditions reduce the costs of breeding.

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Dr. Evans adds “Looking ahead to the future, our data suggest that every single plausible climate change scenario will lead to a further increase in long-tailed survival rates. While many species struggle to adjust to climate change, these delightful birds seem likely to be winners.”

The Rivelin Valley long-tailed tits featured in BBC’s Springwatch this year. To see the videos, go to:

http://www.bbc.co.uk/programmes/p01b7d6g – nest building behaviour

http://www.bbc.co.uk/programmes/p01bb1zf – chick provisioning and helping behaviour

Posted by: oikosasa | March 18, 2014

Effect of coffee farming on soil biota

What happens in the soil when forests are replaced by monocultures? Find out in the Early View paper “Habitat-specific positive and negative effects of soil biota on seedling growth in a fragmented tropical montane landscape” by Camila Pizano and co-workers. Below is the author’s summary of the study:

Pizano2

In this study we showed evidence that when montane tropical forests are replaced by monocultures of coffee and pasture grasses, plant-soil interactions change. Plant-soil interactions have been found to mediate the coexistence between plant species, and maintain biodiversity across a wide array of habitat types. However, we still have a poor understanding on how these interactions vary across neighboring habitat types dominated by different plant species. Furthermore, there are few studies on plant-soil interactions that have been done in both the greenhouse and the field.n this study we showed evidence from the greenhouse and the field that when montane tropical forests are replaced by monocultures of coffee and pasture grasses, plant-soil interactions change. Pastures accumulate soil organisms that are detrimental to pasture grasses and slow growing shade-tolerant tree species but are beneficial for fast growing, pioneer forest tree species. Forests accumulate soil organisms detrimental for pioneer species, but beneficial for slow growing, shade-tolerant forest tree species. And coffee plantations contain soil organisms that enhace the growth of pasture grass and pioneer forest tree species, but decrease the growth of shade-tolerant forest trees. These results suggest that the soil biota present in agricultural lands benefits primary sucession of montane tropical forests, but hinder the establishment of late sucessional forest species. Soil organisms in pastures also hinder the growth of pasture species that are important for cattle production.

Pizano3Pizano3

Posted by: oikosasa | March 17, 2014

Bigger fishes are more predictable

How accurate are different forecast models for predicting population dynamics? That, and how predictable various animals actually are, was tested in the study “Complexity is costly: a meta-analysis of parametric and non-parametric methods for short-term population forecasting”,  by Eric J. Ward and colleagues, that is now published online in Oikos. Below is the author’s summary of the study:

Forecasting ecological data presents a unique set of challenges compared to other types of time series data (stock prices, weather) – two of the most common sources of uncertainty arise from (1) scientists not measuring populations perfectly, and (2) mechanisms responsible for population fluctuations are generally complex and not measureable at a population-wide scale (e.g. density dependence). Many ecological and fisheries models are made complex in an attempt to capture biological realism. Recent work on simulated and real datasets (Perretti et al. 2013 PNAS; Sugihara et al. 2012 Science) has shown that more accurate predictions can be made from simpler non-mechanistic models. Our paper presents the results of a forecasting competition, comparing a wide range of time series models to ~ 2400 time series, representing a range of vertebrate taxa. We found that in general, the best 1-5 year forecasts originated from simple models, such as a random walk (where the predicted population size is the current population size). Taxa that have strongly cyclic population dynamics, such as sockeye salmon, are the easiest to forecast, and warrant the use of more complex types of non-mechanistic models. Across all marine fish species, we found that longer lived species, or those with larger body size are easier to predict (presumably because they have smaller recruitment variability). Similarly, for birds, we found that higher trophic levels were also correlated with better predictions.

sockeye_armstrong

All of the time series included in our analysis were relatively long in ecology (25 continuous data points). The failure of many of the methods we considered suggests that improvement in forecasting ability is unlikley to come from better non-mechanistic forecasting methods or more annual population data; instead we recommend that efforts be made to better understand environmental drivers, which can be included as covariates.

cohoSockeye_armstrong

Posted by: oikosasa | March 14, 2014

Top-predator effects on variable environments

Thanks to giant water bugs’ ferocious feeding habits and their extreme natural environment, authors Kate S. Boersma and colleagues, now have a greater understanding of how biological communities may respond to predator extinctions under increasing global environmental variability. All after having performed the study “Top predator removals have consistent effects on large species despite high environmental variability” published Early View in Oikos. below is their summary of the study and a presentation of the giant water bug.

We used the giant water bug system to explore the consistency of top predator effects in ecological communities that experience high local environmental variability. We experimentally removed giant water bugs from arid-land stream pool mesocosms in southeastern Arizona, USA, and measured natural background environmental conditions. We inoculated mesocosms with aquatic invertebrates from local streams, removed giant water bugs from half of the mesocosms as a treatment, and measured community divergence at the end of the summer dry season. We repeated the experiment in two consecutive years, which represented two very different biotic and abiotic environments. We found that giant water bug removal consistently affected large-bodied species in both years, increasing the abundance of mesopredators and decreasing the abundance of detritivores, even though the identity of these species varied between years. Our findings highlight the vulnerability of large taxa to top predator extirpations and suggest that the consistency of observed ecological patterns may be as important as their magnitude.

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Giant water bug (Abedus herberti) consuming a dragonfly nymph (Oplonaeschna).

At ~3cm in length, giant water bugs (Abedus herberti) may appear unlikely top predators. Yet these aquatic invertebrates dominate the food webs of many small headwater streams in the arid southwestern United States. Giant water bugs use raptorial forelimbs to immobilize prey and piercing mouthparts to inject digestive enzymes and consume the liquefied tissue, allowing them to consume large vertebrate and invertebrate prey. These insects are flightless and thus highly vulnerable to changing hydrology caused by increasing droughts and anthropogenic water withdrawals in arid regions. Streams containing giant water bugs are characterized by seasonal flood/drought cycles and high natural environmental variability, making this an ideal study system to address fundamental questions about the relationship between predator loss and an increasingly variable abiotic environment.

Posted by: oikosasa | March 13, 2014

Which fruit should I choose?

“Which fruit should I eat?” – a decision both migratory and resident birds have to make over and over each autumn. This decision – and the consequences of it is studied in the Early View paper “Consistency and reciprocity of indirect interactions between tree species mediated by frugivorous birds” by Daniel Martinez and co-workers. Below is the authors’ summary of the paper:

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Do fruiting plants compete or facilitate each other for frugivores providing seed dispersal? This question has been previously answered through single-species, short-term studies, that have evidenced indirect interactions between plants. Nevertheless this leaves unanswered another important question. How variable through time and across species within a community are these interactions? Resolving this question will help us to reveal the actual relevance of these interactions in natural systems.

Rodrigues 2Rodrigues3

Our study was developed in a straightforward plant-frugivore system. Three species of fleshy-fruited trees (hawthorn Crataegus monogyna, holly Ilex aquifolium and yew Taxus baccata) coexist in the secondary forest of the Cantabrian mountain range (NW Spain). Their seeds are mainly dispersed by a common assemblage of frugivorous blackbirds and thrushes (Turdus spp.). During autumn and winter both resident and wintering birds have to choose where to feed, among the fruiting trees belonging to the three plant species. Decisions are taken not only considering a given individual tree, but also the trees standing in its neighborhood, with the aim of optimizing in which to perch.

Rodrigues4

Far from general patterns of competition and/or facilitation between these tree species, we find that, like often in nature, variability seems to be the rule. The arising of indirect interactions and their sign shifted between species and across years.  Plant-frugivore systems, even those simple like this, are functionally complex. The abundance and spatial distribution of fruits changed from year to year. While some tree species increased their crops other became scarce. Birds faced very different fruiting scenarios every autumn and, thus, the costs and profits of feeding on different trees changed from year to year.

Rodrigues5

We do not attempt to explain the rules driving indirect interactions within a community, but to show their complexity, consistency between years and reciprocity between species. Taking this variability into account is crucial to understand the role of indirect interactions in the structuring of natural communities.

Artwork and photo credits: Daniel Martínez.

Posted by: oikosasa | March 12, 2014

Ecosystem engineering in food-webs

Ecosystem engineering, the physical modification of the environment by organisms, may well be the most common kind of non-trophic interaction – nearly as ubiquitous as eating and being eaten, and often as influential. Because species are affected by the physical environment, and because all ecosystem engineers belong to food webs while also modifying the environment, their dual role is potentially one of the most important bridges between the trophic and non-trophic. For example, many ant species are predators and important earth movers (see picture). Nevertheless, research in both areas has remained largely independent.

Myror

An upcoming paper (“Integrating ecosystem engineering and food webs” by D. Sanders, C.  Jones, E. Thébault, T. Bouma, T. van der Heide, J. van Belzen, and S. Barot) explores how to integrate ecosystem engineering and food webs. The paper provides rationales justifying integration, and then a framework for understanding how engineering can affect food webs and vice-versa, and how feedbacks alter dynamics. A simple food chain model is then used to illustrate the dynamics in the presence and absence of extrinsic environmental perturbations. The paper argues that current understanding of how engineering shapes food webs and vice versa is perhaps more hampered by lack of knowledge about food web responses to abiotic change than knowledge about how ecosystem engineers can cause such change; and that this is compounded by the fact that engineering and food web studies are rarely studied together in the same system. The authors argue that with appropriate studies and integrative models, conjunction is achievable, helping pave the way to a more general understanding of interaction webs in nature.

Ecosystem engineering and predation by Formica ants (photo credit Dirk Sanders)

Posted by: oikosasa | March 11, 2014

Modelling of human-driven changes in meta-communities

What will happen at the meta-community level with all exposure to human activities in various ecosystems? To answer this, Anne Teyssèdre and Alexandre Robert have simulated a few alternative, presented in the Early View study “Contrasting effects of habitat reduction, conversion and alteration on neutral and non neutral biological communities”

Below is the author’s summary of the paper:

How can we explain the local coexistence of numerous ecologically similar species in the same trophic level communities (like plant, perching bird, or rodent communities), and how will these communities react to the current massive global habitat changes driven by human activities?

While these two questions are necessarily linked, scientists’ current answers seem contradictory. On one hand, Hubbell’s (2001) neutral theory of biogeography and biodiversity (NTB) succeeds to explain – and even predict – many community patterns observed and measured by biologists and biogeographers for several decades, among which the well-known “Arrhenius law”, or power law species-area relationship (SAR). [First proposed by Arrhenius in 1921, this empiric ‘law’ relates the richness at equilibrium (S) of a same trophic level community, in number of species, to the area (A) it occupies, in a power relationship: S = c.Az]

Hubbell’s NTB assumes that the small ecological differences among the species composing a community can be neglected confronted to the large stochasticity (i.e. randomness) of local colonization, reproduction, extirpation and speciation events. It assumes the ecological and demographic equivalence of all species in the community at a local scale, in other terms. But this assumption clearly contradicts many biological and evolutionary data, among which the mere fact of evolution by natural selection. [Hubbel’s neutral model must hence be considered as a useful null hypothesis to confront other community dynamics models, and to explore the correlates of “ecological drift”, like Kimura’ s neutral theory of genetic evolution may be used to explore the correlates of genetic drift.]

To tackle this intriguing issue, we modeled the dynamics of different species communities confronted to different types of habitat changes. More explicitly, we defined a small number of species categories differing in their level of specialization to different habitat types and explored the impact of different simulated habitat changes on a regional community mixing generalist and specialist species (specialization model), compared to that of a community composed of ecologically equivalent species (neutral model), combining stochastic, deterministic and selective processes.

We noteworthy found that (i) both models ruled with habitat reduction predict an approximately power law SAR, in conformity with empirical observations; (ii) with the specialization model, but not with the neutral one, habitat conversion (i.e. land use change) and alteration (e.g. aridification, acidification, eutrophization…) may increase regional species richness until a threshold; (iii) habitat alteration, with the specialization model, leads to the rarefaction of specialist species and the expansion of generalist species, i.e. to the functional homogenization of the community at local and regional scale.

While not predicted by the NTB, these two later patterns are currently observed in many local or regional communities confronted to habitat changes.  We conclude that this kind of model mixing a few stochastic, deterministic and selective processes may be use to explore and anticipate the dynamics and biodiversity patterns of living communities at different geographic scales, in response to different environmental strategies and scenarios.

Posted by: oikosasa | March 7, 2014

Factors affecting carbon cycling in Sphagnum

Now on Early View: A study about functional traits in Sphagnum and how it affects carbon cycling. “Tradeoffs and scaling of functional traits in Sphagnum as drivers of carbon cycling in peatlands” by C.G. Laing and co-workers. Below is the author’s own summary of the study:

The effect of temperature on the decomposition of vegetation has been extensively studied within the climate debate. However, the functional traits of vascular plants have been shown to strongly effect decomposability independently of temperature.

Laing1

Our study  in Oikos explored whether functional traits could explain decomposition of the peat-forming moss Sphagnum since its growth plays a substantial role in global carbon storage.  We coupled classical approaches with the first allometric scaling calculations for Sphagnum to identify water and light availability as controls on growth strategy that impact decomposition rates. It is our hope that our fellow researchers will test the scaling relationships developed here further.

Laing2

Image: Sample collection 07-09-2010 on Ryggmossen Bog, Sweden

Posted by: oikosasa | March 5, 2014

Ecological networks and inference

If many mouths eat a lot of a not so preferable foot item – i.e. large numbers of city rats happen to live underground where they only have access to garbage-like food items – this does not tell us that another foot item not accessible to the crowd is genuinely much more preferable – which rat would refuse to snack on gourmet cheese if there wouldn’t be obstacles that allow only brave foragers to have a bite on it?

dreamstime_m_14830510

In ecological network studies, species preferences are often summarized as to how often species interact with each other for multiple species.  This can be foragers feeding on different resources, for example.

While indices and summary statistics for explaining resulting network structure have experienced much sophistication in recent years, the fact that interaction frequencies are the product of preferences / attraction towards interacting partners and availability / abundance of interacting species has received little attention.

The early view paper “Population fluctuations affect inference in ecological networks of multi-species interactions” by Konstans Wells and co-workers, shows that population fluctuations have considerable impact on calculated network statistics. So an increasingly large range of values can be inferred from the same ecological system the more populations fluctuate.  Considering  abundance fluctuations and sampling effort in ecological networks may not only improve inference, but also open promising perspectives to novel questions in ecological research  – certainly if the crowd makes it to the most preferable piece of meal, this will affect all aspects from individual behaviour to what is left on the plate for the next round of interactions, be it for single species or communities.

Posted by: oikosasa | March 4, 2014

Invasive flowers, pollinators and native flowers

How different kinds of ecological aspects affect the future of invasive plants is studied in the Early View paper:“Neighborhood-contingent indirect interactions between native and exotic plants: multiple shared pollinators mediate reproductive success during invasions” by Susan Waters and co-workers. Below is the author’s summary of the study:

In the highly fragmented prairies of western Washington’s Puget Trough, conservation focuses on managing invasive plant species that may directly compete with rare native forbs.  However, the area also has a depauperate pollinator community, and the highly overlapping assemblage of generalist pollinators visiting native and exotic dandelion-like forbs suggested to us that native and exotic plants might also interact indirectly through pollinators (for example, by competing for pollinator visits, or by altering the amount of conspecific pollen transferred to a neighbor). 

flowersGiven that one of the dominant invaders, Hypochaeris radicata, has a patchy distribution, and that pollinators often alter their foraging patterns in response to floral density, we speculated that pollinator-mediated indirect interactions might play out differently in H. radicata-dominated floral neighborhoods than in less-invaded, more diverse floral neighborhoods. 

However, further observation soon caused us to suspect that the story was more complex. There were multiple pollinator intermediaries between the plants, and we realized that pollinator groups might differ in their responses to different floral neighborhoods. We hypothesized that there were at least two ways that floral neighborhoods might alter pollinator behavior: either by changing whether pollinators chose to forage in the patch at all, or by changing the foraging decisions pollinators made once they arrived in the patch.

hypfig

We compared pollinator visitation and seed set by two native forbs and H. radicata in three floral neighborhoods: high density native (and low density H. radicata), high density H. radicata (and low density native) and low density of both H. radicata and natives. Eusocial bees, solitary bees, and syrphid flies all visited the H. radicata and the two native forbs we observed, but the proportion of total visitation to a plant species from each pollinator group depended on the floral neighborhood.  Accordingly, dense exotic H. radicata neighborhoods facilitated seed set in one native forb, Eriophyllum lanatum, while diminishing seed set in another native forb, Microseris laciniata.  Context-dependent pollinator visitation, mediated by multiple pollinators, thus resulted in opposing effects of an exotic plant on two native species.

Posted by: oikosasa | March 3, 2014

Welcome Martijn Bezemer, new SE

We’re very happy to welcome Dr Martijn Bezemer, NIOO-KNAW, the Netherlands to our editorial board.

Bezemer martijnMartijn, what’s your main research focus at the moment?
My main research focus is on aboveground-belowground interactions. I study how (i) soil biota (ii) manipulations of the soil community, and (iii) soil mediated effects of neighbouring plants affect the nutritional quality of focal plants and the aboveground plant-insect interactions on those focal plants. Further, I study the role of soil organisms in restoration of grasslands on former arable land. Much of this work is carried out in the field.

Can you describe you research career?

My MSc was in Crop Protection in Wageningen, The Netherlands. I started my carreer at Imperial College at Silwood park, where I studied the effects of elevated CO2 and elevated temperature on plants, insects and parasitoids in model ecosystems in the ecotron controlled environment facility. This was from 1995 to 1999. From 1999 to 2000 I went to UC Berkeley for a post-doc. Here I studied biological control of codling moth in walnut orchards using introduced parasitoids. In nov 2000 I moved back to the Netherlands for a post doc at the Netherlands Institute of Ecology (NIOO). I first studied the effects of root herbivory by wireworms on aboveground plant-insect interactions in cotton and then worked on the effects of aboveground and belowground multitrophic interactions on plant diversity and succession. In 2004 I moved to Wageningen University but continued working on linking aboveground and belowground diversity. In 2008 I am moved back to the NIOO, and I have a position as senior scientist.

Bezemer field

How come that you became a scientist in ecology?

During my MSc I focused agronomy. My stay at Silwood Park made me an ecologist.

What do you do when you’re not working?

I like to play guitar, read literature and DIY type activities in our house

Posted by: oikosasa | February 28, 2014

Editor’s Choice Feb-March 2014

DriesFor the February and March issue we have selected three articles as Editor’s choices that are currently open access. We selected papers that are at the heart of our publication mission, so papers that aim at providing synthesis in ecology. The work by Sergio Estay and colleagues focusses on the role of temperature variability for insect performance, and how these individual changes in performance feedback on population dynamics. The work is theory-based and provides a framework to organize research of the role that thermal mean and variability plays in individual performance, and how it may affect population dynamics. By developing null models, they demonstrate that potential changes in the intrinsic population growth rate depend on the interaction of mean temperature and thermal variability, and that the net effect of the interaction could be synergistic or antagonistic. The theoretical models are evaluated using data compiled from literature.

A promising avenue to test these theoretical predictions is using experimental microcosms. While it remains questionable to which degree such small-scale studies scale up to macroscopic patterns, they allow a tight coupling between simple models and real data that are collected in a standardized manner. Clements and colleagues followed this approach to test the effects of directional environmental change on extinction dynamics in experimental microbial communities as predicted by a simple model. Based on the assumption that temperature does alter an individual’s metabolic rate, and consequently birth and death rates, they predict that in declining populations, these alterations may manifest as changes in the rate of that population’s decline, and subsequently the timing of extinction events. Clements and colleagues find that extinction occurs earlier in environments that warm faster, and importantly that phenomenon can be accurately predicted by a simple metabolic model. Increasing the number of parameters that were temperature-dependent increased the model’s accuracy, as did scaling these temperature-dependent parameters.

 

The last Editor’s choice for now is the Per Brinck contribution from 2013 by Sharon Strauss: Ecological and evolutionary responses in complex communities: implications for invasions and eco-evolutionary feedbacks. In this contribution, Strauss discusses our current understanding on how interactions between ecological and evolutionary dynamics affect the organization and functioning of simple and more complex communities. Based on her own work and that of many others, she examines how community complexity may influence the nature and magnitude of these eco-evolutionary feedbacks, and how an escape from community complexity per se affects the success of invaders. She synthesizes the diverse dynamics into three general types: those generating alternative stable states, cyclic dynamics, and those maintaining ecological stasis and stability.

 

Posted by: oikosasa | February 27, 2014

Cows and rabbits change plant growth via the soil

How does grazing affect the soil? Find out in the Early View paper “Grazing-induced changes in plant–soil feedback alter plant biomass allocation” by Ciska van Veen and co-workers.

Cows and rabbits, feed on plants. With that they change plant growth directly, for example by removing leaves. In addition they may change an array of soil conditions, such as the amount of nutrients or root feeders in the soil. In this study we found that these changes in the soil from grazed grasslands influenced plant growth (photo 1).

Coxsandrabbits1

Photo 1: greenhouse experiment where the researchers investigate the growth of different plant species in soils from grazed and ungrazed grasslands.

However, the impact of cows and rabbits on plant growth via changes in the soil, did not help us to understand the species composition of plants in the field (photo 2). Thus, the direct influence of cows and rabbits on plant growth seems more important for plants in the field.

Photo 2: field experiment in the Junner Koeland Nature Reserve (the Netherlands). Cows and rabbits are excluded with fences from parts of the nature reserve. The researchers used the soil from inside and outside the fences to test the response of plant species. In addition, the researchers monitored the plant species composition inside and outside the fences to test if the response of the plants to the different soils could help to understand the plant species composition.

Photo 2: field experiment in the Junner Koeland Nature Reserve (the Netherlands). Cows and rabbits are excluded with fences from parts of the nature reserve. The researchers used the soil from inside and outside the fences to test the response of plant species. In addition, the researchers monitored the plant species composition inside and outside the fences to test if the response of the plants to the different soils could help to understand the plant species composition.

Posted by: oikosasa | February 25, 2014

Most downloaded 2013 papers

Recently, Wiley released the list over most downloaded Oikos papers during 2013. Many of the papers are familiar titles, that were published a few years ago. However, two of the papers published during 2013 actually managed to climb the ladder and take place among the top ten. Both of them were presented at this blog. Both of them were selected as Editor’s choice.

Here’s a link to the top 10 list:

http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1600-0706/homepage/MostAccessed.html

The two 2013 papers have been opened for Free Download by Wiley for the next two weeks, so take your chance to download them today! And the papers are:

Is the Oikos chief editor the only one working? Dries is busy handling manuscripts while James and Maria dream of seeds and eagle owls, respectively!

Is the Oikos chief editor the only one working? Dries is busy handling manuscripts while James and Maria dream of seeds and eagle owls, respectively!

Dispersal and species’ responses to climate change with 1384 downloads

by J. Travis et al.

Link to paper: http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0706.2013.00399.x/full

Link to blogpost: http://oikosjournal.wordpress.com/2013/09/13/dispersal-at-the-heart-of-our-thinking/

and

The elephant in the room: the role of failed invasions in understanding invasion biology with 1604 downloads

by Zenni and Nunez

Link to paper: http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0706.2012.00254.x/full

Link to blogpost: http://oikosjournal.wordpress.com/2013/02/01/the-elephant-in-the-room/

Posted by: oikosasa | February 21, 2014

Bottom-up effects of hybridization

A hybridization event at the bottom of the food chain may affect organisms several steps up the chain. Read more in the early View paper: “Bottom–up regulates top–down: the effects of hybridization of grass endophytes on an aphid herbivore and its generalist predator” by Susanna Saari et al. 

Below is their popular summary of the study:

Hybridization is a well understood process where organisms fuse to form new organisms with unique characteristics. However, the ecological consequences of hybridization in the microbial partners of plants are largely unknown. We studied the effects of hybridization of microbial plant symbionts on the feeding preference and performance of herbivores and their natural enemies. In our laboratory experiments, we used the grass Arizona fescue as the host plant, Neotyphodium endophyte as the microbial plant symbiont, the bird cherry-oat aphid as the herbivore and the pink spotted ladybird beetle as the predator. Neither endophyte infection (infected or not infected) nor hybrid status (hybrid or non-hybrid) of the endophyte affected aphid reproduction, aphid host plant preference or body mass of the ladybirds. However, development of ladybird larvae was delayed when fed with aphids grown on hybrid endophyte infected fescue compared to ladybird larvae fed with aphids reared on either non-hybrid infected fescue, non-hybrid, endophyte-removed fescue and hybrid, endophyte-removed fescue.

A pink spotted ladybird and bird cherry-oat aphids on Arizona fescue. In our experiment, pink spotted ladybirds avoided aphids that had been feeding on grasses infected with hybrid Neotyphodium endophytes.

A pink spotted ladybird and bird cherry-oat aphids on Arizona fescue. In our experiment, pink spotted ladybirds avoided aphids that had been feeding on grasses infected with hybrid Neotyphodium endophytes.

Furthermore, adult ladybrids were more likely to choose all other types of fescues harboring aphids rather than hybrid endophyte infected fescues. Our results suggest that the hybridization of microbial symbionts may negatively affect predators such as the pink spotted ladybird and protect herbivores like the bird cherry-oat aphids from predation even though the direct effects on herbivores are not evident.

Neotyphodium endophyte (red lines) growing between the cells (the red circles) of a plant. Endophytes are micro-organisms growing within the tissues of plants without causing any symptoms for the host. Some fungal endophytes can fuse with other fungi growing within the tissues of the host plant thereby forming a hybrid fungus with unique characteristics.

Neotyphodium endophyte (red lines) growing between the cells (the red circles) of a plant. Endophytes are micro-organisms growing within the tissues of plants without causing any symptoms for the host. Some fungal endophytes can fuse with other fungi growing within the tissues of the host plant thereby forming a hybrid fungus with unique characteristics.

Ecological synthesis is tricky. One of its many challenges is that empirical data rarely paint a clear picture either supporting or refuting a given hypothesis. More typically, empirical studies have diverging results. But even for hypotheses where refuting evidence is overwhelming, ecologists are often reluctant to abandon them (see Oikos Blog on Zombie Ideas).

In our paper “The enemy release hypothesis as a hierarchy of hypotheses” (Heger & Jeschke in Oikos, early view), we explore a novel method for assessing ecological hypotheses based on empirical evidence: the Hierarchy-of-Hypotheses (HoH) approach. This approach was born during a joint project (see Jeschke et al. 2012 in Neobiota) and a workshop titled ‘‘Tackling the emerging crisis of invasion biology: How can ecological theory, experiments, and field studies be combined to achieve major progress?’’ (see Heger et al. 2013 in Ambio). When we discussed the problem of imprecise formulations of hypotheses in invasion ecology (another challenge to ecological synthesis), it became obvious that we need a framework for integrating both broad and narrow hypotheses. Our suggestion for such a framework is the HoH approach, where a broad, overarching hypothesis branches into increasingly narrow and specific formulations of this hypothesis (i.e. sub-hypotheses). The most specific formulations are empirically testable.

The HoH approach can serve as an organizational tool (e.g. to structure research questions, or to organize conceptual work), but also for assessing hypotheses. In our paper, we show the first worked-out example for a HoH. We used the method for a well-known and much discussed hypothesis of invasion ecology: the enemy release hypothesis. Applying a newly developed weighting procedure, we assessed empirical evidence for each sub-hypothesis. Our results show that overall, there is nearly as much evidence in favor as against the enemy release hypothesis; hence, the overall picture is quite blurry. However, a closer look at the sub-hypotheses reveals that specific formulations of the enemy release hypothesis are clearly empirically supported, whereas other formulations receive hardly any support (see Fig. 1). This example shows how powerful the HoH approach can be to make a blurry picture clear.

 SantaCalus

Figure 1. Schematic illustration of a hierarchy of hypotheses (HoH) for the enemy release hypothesis. The scheme classifies empirical tests of the enemy release hypothesis according to three criteria, shown as three hierarchical levels: (1) indicator for enemy release; (2) type of comparison; and (3) type of enemies. The combination of these criteria results in different sub-hypotheses which are drawn as boxes; the number of empirical tests available for each sub-hypothesis is given in the respective box (‘n’). The boxes are color-coded as follows: red boxes: 50% or more of the data question the sub-hypothesis, and n≥5; green boxes: 50% or more of the data support the sub-hypothesis, and n≥5; white boxes: all other cases (i.e. n<5 or inconclusive data).

In writing the paper, we had several discussions on how much empirical support is needed to call a hypothesis ‘supported’. For Fig. 1, we agreed on the threshold of 50% support, but this is debatable. We believe that ecology needs a discussion on these questions: How do we decide whether a hypothesis is worth keeping? How much supporting evidence is needed, and how much refuting evidence can be tolerated? We very much hope that our paper stimulates discussions on these and similar questions. Also, it would be great to see more HoHs being created, in ecology and beyond.

Tina Heger & Jonathan M. Jeschke

Posted by: oikosasa | February 14, 2014

Bob Holt – prize winner 2014

Last week, the annual Oikos meeting was held in Stockholm. This year as a Nordic event, with speakers from both Sweden, Norway, Denmark, Finland and Iceland.

The big happening was of course, that Prof. Bob Holt was awarded the Per Brink award.

Bob gave a fantastic talk, managing to turn theoretical ecology to an exciting fairytale!

Bobs talk

After the talk, Oikos’ Editor in Chief, Dries Bonte and Managing Editor, Åsa Langefors (on the photo) handed over the diploma and the glass apple.

Bob prize

The diploma is a wonderful piece of artwork, painted by biologist and artist Linnea Fredriksson http://linnea.linneaartline.com Linnea reads most of the awardee’s scientific work and uses the study species and focus to create the picture.

Take a closer look at Bob’s diploma:

Diploma

Congratulations Bob! http://people.biology.ufl.edu/rdholt/

Posted by: oikosasa | January 31, 2014

Salmon response to climate variations

Why might you find scientists out on a pitch black night on a remote Alaskan lake driving two 18’ boats with a net towed in between?  Fun, tradition, data collection?   Well, all of the above, assuming the weather is nice.  In our article, “Climate variation is filtered differently among lakes to influence growth of juvenile sockeye salmon in an Alaskan watershed,” we rely on generations of scientists doing just this to evaluate how juvenile salmon growth responds to climate variability.

Long-term datasets provide opportunities to disentangled pattern from noise.  Establishing and maintaining long-term datasets requires marshalling the human, financial, and logistical support necessary to return year after year to collect data.  The University of Washington’s Alaska Salmon Program (http://fish.washington.edu/research/alaska/ or https://www.facebook.com/AlaskaSalmonProgramFRI) has been sending scientists to remote southwest Alaska since the mid-1940s to collect data on juvenile sockeye salmon and their habitats.

Griffiths_FieldCamp2_OIK-00801R2

Our field methods today are remarkably similar to those established over 60 years ago.  Every summer at the end of August, we head out onto our study lakes (in this case, Chignik and Black lakes) on small boats just as the sun is heading down.  Armed with a net that looks a like a gigantic windsock with arms, flashlights, a GPS, and trays and buckets, we get ready to capture and measure juvenile sockeye salmon.  Juvenile sockeye salmon feed near the surface at night making them more easily sampled by our nets.  We tow the net between our “master” and “slave” boats according predetermined tracks, hoping to steer far clear of shore.  After towing for a set time, we haul in the net and inspect our catch.  Fish we catch are subsampled and brought back to our field station to be measured and weighed.

Griffiths_MeasuredSockeye_OIK-00801R2

By sampling year after year, we can observe the variation in juvenile sockeye salmon growth during their first summer of life and evaluate causes of variation in growth.  Growth is an important determent of their ability to avoid predators as well as survive winter conditions and ocean migration.  In our study we investigated if the year to year variability in growth was explained by climate variation, including differences among years in winter and spring air temperature.  Using additional information regarding juvenile salmon growth collected from adult sockeye scales, we were also able to investigate whether the same regional climate such as air temperature elicits the same growth response from juvenile salmon in different lake types.

Griffiths_FieldCamp1_OIK-00801R2

We found that the average size of juvenile salmon has been increasing over time.  However, the same changes in air temperatures did not always lead to the same response in juvenile salmon growth in different lake types.  Juvenile sockeye salmon grew larger in years with warmer spring and fall temperatures in deep, cold Chignik Lake.  Just upstream in shallow, warm Black Lake, juvenile salmon grew less in years with warmer air temperatures.  These differences in growth indicate that landscape diversity within watersheds filters climate such that organisms experience and respond differently among habitats. Our ability to manage for resilient ecosystems in the face of ongoing environmental change may be improved by considering within, as well as among, watershed climate filtering.

Posted by: oikosasa | January 27, 2014

To live in a multi-predatory landscape of fear

Having one predator chasing you is scary enough, but what about having two? Hunting in different habitats? Lucky me not being  roe-deer! Read more in the Oikos Early View paper “Living and dying in a multi-predator landscape of fear: roe deer are squeezed by contrasting pattern of predation risk imposed by lynx and humans” by Karen Lone and colleagues. Below is Karen’s summary of the paper:

The challenge of managing large carnivores in a multiple-use landscape in Norway has motivated a large research effort to understand carnivore ecology and their impact on livestock and other wildlife, in addition to extensive monitoring. I was lucky to be able to use some of the data collected in this larger framework to investigate predator-prey interactions and the landscapes of risk for roe deer. Our goal was to look at the effect of multiple predators preying on a single prey species. Roe deer have a natural predator in lynx, and a functional predator in hunters. We investigated how predation risk from these two predators related with habitat characteristics by comparing kill sites to sites used by live roe deer, and anticipated that they produced conflicting landscapes of risk.

LiDAR data from one field plot with radius ca 28m in a 3D perspective – points are colored by height above the ground, so vegetation hits stand out in warmer colors than ground hits.

LiDAR data from one field plot with radius ca 28m in a 3D perspective – points are colored by height above the ground, so vegetation hits stand out in warmer colors than ground hits.

In this paper we try to use Light Detection and Ranging (LiDAR) data to predict risk. We had access to a LiDAR dataset obtained by airborne laser scanning the entire 900km2 study area. As well as giving spatially extensive information, it also gives a lot of detail: the point cloud of height measurements (points at which laser beam was reflected) gives a nice visual impression of vegetation structure (see figure). Especially important LiDAR variables in our analysis of risk were laser echoes from the 0.5-2m height segment, corresponding to the density of the understory vegetation. The final predictive maps of predation risk are based on LiDAR data, a terrain model and a map of roads.

Our study site Hallingdalen, a valley in central Norway, is a multiple-use landscape.

Our study site Hallingdalen, a valley in central Norway, is a multiple-use landscape.

Both LiDAR data and field data provided the same findings – that predation risk from lynx was higher in denser habitat, and increasing with distance from roads. Conversely, the risk of being killed by a hunter was higher in more open habitat and closer to roads, indicating that roe deer face a trade-off between the two predators along these gradients. With regards to some habitat characteristics, the risk gradient aligned for lynx and hunter – both inferred greater risk in more rugged terrain. From the spatial predictions, we found that only 1% of the area had low predation risk from both predators. In other words, when we considered two predators together rather than each on their own, the roe deer had almost no refuges where they can escape predation altogether. Our study raises questions of how roe deer adapt their behavior, if at all, to reconcile the risk landscapes they face, and whether the temporal variations between their two predators may be the key to avoiding mortality.

Posted by: oikosasa | January 24, 2014

Editor’s Choice January 2014

DriesThe first editor’schoice for 2014 is the work of Alexander Kubisch and colleagues. This invited contribution synthesizes how feedbacks between ecological and evolutionary on dispersal shape species ranges and range dynamics. The manuscript is a systematic review on the existing literature and prevailing insights combined with novel modeling approaches to demonstrate the relevance of evolutionary forces at all hierarchical levels of biological organization (from landscapes to communities via populations, individuals and genes) that affect distribution ranges. Since Oikos has been publishing many relevant key-papers in this field, the authors have additionally compiled a virtual issue which will be available in January and which is introduced here. Alexander Kubisch won the Horst-Wiehe-prize at the GfÖ annual meeting for this synthesizing range biology work.

Synthesis: What factors are responsible for the dynamics of species’ ranges? Answering this question has never been more important than today, in the light of rapid environmental changes. Surprisingly, the ecological and evolutionary dynamics of dispersal – which represent the driving forces behind range formation – have rarely been considered in this context. We here present a framework that closes this gap. Dispersal evolution may be responsible for highly complex and non-trivial range dynamics. In order to understand these, and possibly provide projections of future range positions, it is crucial to take the ecological and evolutionary dynamics of dispersal into account.

The second editor’s choice for January is the research paper by Qi and colleagues. They analysed a large trait database involving 1355 species from the northeastern verge of the Tibetan Plateau to test to which degree seed mass is affected by changing abiotic conditions along altitudinal gradients. The analysis of such a large dataset revealed the relevance of two opposing forces, stress tolerance and energy constraints. Subsequently, life history cycles, resource allocation strategies and dispersal agents appeared to be more important drivers in seed mass than pollination efficiency along a pronounced latitudinal gradient. Clearly, only an integrated analysis of the potential drivers of a single trait like seed size may lead to such comprehensive insights.

Synthesis: With increasing elevation, seed mass may be either larger for its advantage during seedling establishment (‘stress-tolerance’ force), or smaller owing to energy constraints. Our paper shows some novel and importance results in the seed mass–elevation relationship in a northeastern Tibetan flora. Firstly, these two opposing forces operate simultaneously but overall balance out one another. Secondly, the balance tends to shift toward increased energy-constraints (stress-tolerance) with the increase (decreased) in average seed mass. Thirdly, energy constraints on seed mass is indirect and mediated by the variation in plant height. Finally, plant resource allocation pattern, life-history cycle, and availability of dispersal agents can affect the responses of seed mass to elevation.

Dries Bonte

Posted by: oikosasa | January 22, 2014

Vectors’ role in pathogen dynamics

If  a vector prefers uninfected hosts or infected hosts – how does that affect the pathogen’s spread? Find out in the Early View paper “Vector preference and host defense against infection interact to determine disease dynamics” by Adam R. Zeilinger and Matthew P. Daugherty. Here’s a short version of the paper:

Pathogen spread is greatly influenced by the way that vectors choose which host to feed upon.  Epidemiologists have recognized that many vectors make feeding choices based on whether the host is infected with the pathogen or not.  For example, some mosquito species prefer to feed on animals (including humans) that are infected with malaria over malaria-free animals.  Conversely, the glassy-winged sharpshooter—which spreads the causal pathogen of Pierce’s disease among grapevines—prefers healthy plants.

Grapevine1

At the same time, epidemiologists have also recognized that hosts vary in their susceptibility to a disease.  Some hosts are resistant to infection, meaning that the pathogen replicates poorly in them.  Other hosts are tolerant to the disease, meaning that the pathogen can replicate but the host simply does not express disease.  Resistance and tolerance are both forms of defense against a pathogen.

While vector feeding preference and host defense are clearly important for the spread of a pathogen, we were interested in understanding how the two factors may interact to influence pathogen spread.  To begin to understand the relationships between vector preference and host defense, we used a series of mathematical models, similar to SIR models widely used in epidemiology.  The models simulate the spread of a pathogen in interacting host and vector populations under different scenarios for vector preference and host defense.

Grapevine2

We found that host resistance curbed pathogen spread, regardless of whether vectors preferred or avoided disease symptoms.  However, differences in vector behavior resulted in highly divergent effects if hosts were tolerant, with the greatest pathogen spread occurring if vectors avoided symptoms.  This occurs because, by masking infection, tolerance causes more vectors to inadvertently come into contact with infected hosts and acquire the pathogen.  Furthermore, we extended our model to a two-patch model, in which two host populations with differing defenses were connected by vector movement.  The outcomes from those scenarios support the idea that host defense impacts pathogen spillover, with a greater potential for tolerant host to be pathogen sources relative to resistant host types.

These results highlight the importance of understanding both vector feeding behavior and the precise form of host defense in predicting pathogen spread.  This may be particularly important for integrated disease management for agricultural crops.  For example, given that the glassy-winged sharpshooter prefers disease-free grapevines, breeding new grapevine varieties that are tolerant to Pierce’s disease may lead to unexpectedly high disease spread among nearby susceptible grapevine varieties.

Posted by: oikosasa | January 20, 2014

Yiihaa! Oikos new webpage open!

It’s here! Our new webpage is ready and open for everyone to visit!

placeit(1)

Apart from journal information, aims and scopes of Oikos and author guidelines for manuscript submissions, you also find, twitter- and facebook flows, abstracts to newly accepted papers as well as abstracts and links to Early View Papers. The latter with Altmetrics, an article’s impact on the web.

Welcome to visit us at www.oikosjournal.org

The online library is still found at http://onlinelibrary.wiley.com/journal/10.1111/%28ISSN%291600-0706

Submissions are still sent to http://mc.manuscriptcentral.com/oikos

Blog posts will appear both on oikosjournal.wordpress.com, where all old posts are found to, and on our new blog site http://www.oikosjournal.org/blog

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