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

Posted by: oikosasa | January 17, 2014

Per Brink Award 2014

We are very happy to announce that “The Per Brinck Oikos Award 2014″ has been awarded to Professor Robert D. Holt, University of Florida, Gainsville, Florida, USA.

IMG_9565

Here is Bob’s presentation of himself and his research:

What makes the study of life such an endlessly satisfying endeavor is that species and ecosystems reflect both order and change – both the predictable outcome of general laws, and the lingering effects of idiosyncracies of evolution, earth history, and the often surprising feedbacks that arise in complex natural systems.  As a fan of natural history, I appreciate and indeed relish the complexities and unique contingencies of ecological systems, even as in my role as theoretician I seek for unifying principles.  I have carried out research on a wide range of topics, from food web dynamics and host-pathogen interactions, to habitat fragmentation, to the evolution of dispersal and geographical ranges, and have had the good fortune to have collaborated over my career with many outstanding theoreticians and empiricists.  But in my own mind underlying this diversity of specific topics there is a thematic unity, involving on the one hand a concern with teasing apart the forces driving complex ecological systems, and on the other the desire to integrate perspectives from different disciplines, such as evolution, dynamical systems, and behavior, into our understanding of ecological systems. One approach to ecological complexity is to closely examine the direct and indirect interactions among a small number of interacting species – community modules – which can reveal processes at play in much richer webs of interactions.  Another is to recognize the pervasive influence of spatial heterogeneity and dynamics for almost all ecological systems.  Yet another approach is to recognize the intertwining of ecology and evolution.  For example some taxa are very conservative in their ecological niches, whereas others can evolve rapidly and even explosively over short time horizons.  Understanding all these aspects of ecological complexity, and how they are related over both short and long time-scales, is crucial for addressing a wide range of applied problems, from keeping in check invasive species and emerging diseases, to conserving species in altered landscape, to predicting the impacts of climate change.”

OIK_1298_fu1The Per Brinck Oikos Award recognizes extraordinary and important contributions to the science of ecology. Particular emphasis is given to scientific work aimed at synthesis that has lead to novel and original research in unexplorered or neglected fields, or to bridging gaps between ecological disciplines. Such achievements typically require theoretical innovation and development as well as imaginative observational or experimental work, all of which will be valid grounds for recognition.

The /Per Brinck Oikos Award/ is delivered in honor of the Swedish ecologist Professor Per Brinck who has played an instrumental role for the development and recognition of the science of ecology in the Nordic countries, especially as serving as the Editor-in-Chief for Oikos for many years.

The award is delivered annually and the laureate receives a modest prize sum (currently €1500), a diploma and a Swedish artisan glassware. The prize ceremony is hosted by the Swedish Oikos Society. The award is sponsored by the Per Brinck Foundation at the editorial office of the journal Oikos and Wiley/Blackwell Publishing.

Per Brink passed away, at the age of 94 years a few months ago. Read the memorial in Oikos here.

Posted by: oikosasa | January 15, 2014

Invasive mussels as ecosystem engineers

How is lake water quality and nutrient fluxes effected by invasive and native organisms? That’s what Geraldine Nogaro and Alan D. Steinman are answering in the new Early View Oikos paper, “Influence of ecosystem engineers on ecosystem processes is mediated by lake sediment properties”.

Here’s the author’s summary of the paper:

Dreissenid mussels, an iconic invasive species of the Laurentian Great Lakes since their introduction via ballast water in the late 1980s, can greatly alter nutrient fluxes and the microbial food web through their filter-feeding activity and excretion of feces and pseudo-feces at the water–sediment interface. Invasive species may impact biotic community structure, ecosystem processes, and associated goods and services. Their impacts may be especially strong because they also serve as ecosystem engineers (i.e., organisms affecting the physical habitat and resources for other species). The main objective of our study was to determine how the filtering/excretion activity of invasive mussels and the burrowing/bioirrigation activity of native chironomid larvae affect nutrient fluxes and water quality in Muskegon and Bear Lakes (Fig. 1). Laboratory mesocosm experiments were conducted using core tubes filled with sediment, water, and invertebrates (mussels and chironomids) collected from Muskegon and Bear Lakes (Fig. 2).

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Fig. 1. Location of Muskegon and Bear Lakes within Laurentian Great Lakes region in Michigan, USA (top). Muskegon Lake (bottom left) and Bear Lake (bottom right) from the sampling boat.

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Fig. 2. Dr. Geraldine Nogaro sieving sediment from Muskegon Lake to collect burrowing macroinvertebrates and study their influence on nutrient biogeochemistry in impacted lake ecosystems.

Results showed that sediment reworking and ventilation activities by chironomids increased oxygen penetration in the sediment, affecting primarily pore water chemistry, whereas invasive mussels enhanced nutrient releases in the surface water (Fig. 3). However, burrowing chironomids had a greater influence on sediment reworking and microbial-mediated processes in organic-rich sediments (Bear Lake), whereas invasive mussels enhanced nutrient concentrations in the overlying water of organic-poor sediments (Muskegon Lake). These results have management implications, as the effects of invasive mussels on the biogeochemical functioning in the Great Lakes region and elsewhere can alter system bioenergetics and promote harmful algal blooms.

Fig. 3. Sediment cores used to evaluate invertebrate effects on nutrient release (top). Native chironomids created oxygenated burrows (bottom left), while invasive mussels stimulated nutrient release at the sediment surface (bottom right).

Fig. 3. Sediment cores used to evaluate invertebrate effects on nutrient release (top). Native chironomids created oxygenated burrows (bottom left), while invasive mussels stimulated nutrient release at the sediment surface (bottom right).

Reference:

Nogaro G., Steinman A.D. (2013) Influence of ecosystem engineers on ecosystem processes is mediated by lake sediment properties. Oikos doi: 10.1111/j.1600-0706.2013.00978.x

Posted by: oikosasa | January 13, 2014

On the importance of fruit in primate diets

How does fruit-eating relate to body size and geographic range? Find out in the Early View paper “Ecological correlates of trophic status and frugivory in neotropical primates” by Joseph E. Hawes and Carlos A. Peres.

Below is their summary of the study:

A good understanding of non-human primate diets in the wild is vitally important for the conservation planning of threatened species, with forest habitat loss and severe forest degradation a major concern throughout the New World tropics. It is also critical to help evaluate the roles of primates within forest food webs, particularly as seed dispersers for tropical forest plants. Fruit eating is widespread amongst primates although they are rarely entirely frugivorous, with insects, gums and leaves providing alternative food sources.

To explore this variation, we reviewed a comprehensive compilation of 290 primate dietary studies from 164 localities in 17 countries across the entire Neotropical realm. Sampling effort varies considerably between sites and species (Hawes et al. 2013), which we accounted for here when comparing the taxonomic richness of fruiting plants recorded in primate diets, and the relative contribution of frugivory to the overall diet. We also found strong evidence to support the long-held hypothesis that body size imposes an upper limit on insectivory and a lower limit on folivory, and therefore that frugivory is most important at intermediate body sizes.

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Frugivory continuum in relation to body size, showing a peak in medium-sized primates

One of our most surprising finds was that primates with wide geographic ranges do not necessarily consume a wider diversity of fruits, perhaps because these species tend to be generalist consumers. Another surprise was that primates with higher prevalence of fruit in their diets are among the most poorly studied, meaning we still have a lot to learn about their importance as consumers and seed dispersers in tropical forests.

Image credits:

  1. Saguinus oedipus: http://commons.wikimedia.org/wiki/File:Cottontop_tamarin.JPG
  2. Pithecia irrorata: © Edgard Collado
  3. Alouatta guariba: http://commons.wikimedia.org/wiki/File:Southern_brown_howler_monkey_female_sp_zoo_2.JPG

References:

Hawes, J.E., Calouro, A.M. & Peres, C.A. (2013). Sampling effort in neotropical primate diet studies: collective gains and underlying geographic and taxonomic biases. International Journal of Primatology. DOI: 10.1007/s10764-013-9738-0 (in press).

Who are the murderers and who are the victims in forest soils? Read about Babett Günther and co-workers’ homocide investigation in the Early View Oikos paper: “Variations in prey consumption of centipede predators in forest soils as indicated by molecular gut content analysis”. 

Here’s their story about the study:

We all know from TV series like CSI: crime and murder always happen in the dark, in remote and obscure places where the victim is overwhelmed by the sneakily attacking offenders. Killing is not only confined to humans, and the offender may have some good reason to kill, for example predation and nutrition. But what are the circumstances of successful killing and predation? Are there more killings when there are more/smaller/less defensive victims? Or is it the size of the attacker? Or is it because of the structure and topography of the crime scene?

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We tested these hypotheses in one of the most obscure and unearthly environments: the soil and litter layer of different forests. The victims: springtails, dipteran larvae and earthworms. The delinquents: small and large stone centipedes of the genus Lithobius. Just like TV forensic scientists, after rummaging through the dirt, looking for DNA evidence, drinking a lot of coffee and after many long nights in the laboratory, we finally solved the case:

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large centipedes are able to kill more prey at high prey abundances and in unstructured environments, while the opposite was true for small predators. Interestingly, small centipedes were also shown to overwhelm large victims, indicating high criminal energy in small creatures, as has been already demonstrated for humans (e.g. John Dillinger).

In a seminal contribution published in 1972 (Nature, 238; 413-414), Sir Robert May showed that from a mathematical point of view the more complex an ecological community is (in terms of the number of species and interactions in the system), the less stable it is. However, complex ecological communities are observed in nature, and so the issue on how species in large complex ecological communities may coexist is still a relevant and open debate in ecology.

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In recent years several searched for new principles allowing ecosystems to persist despite their complexity, but a general consensus on this topic has not yet been achieved.

Last summer, an intriguing work published in Science (A. Mougi, M. Kondoh, Science 337, 349) claimed that specific mixture of antagonistic (predator-prey) and mutualistic interactions (beneficial for the interacting individuals) between species is likely to contribute to stabilize ecological communities. Furthermore, they also found that in this type of hybrid community “…increasing complexity leads to increased stability”. As mixing of interaction type is the norm rather than the exception in ecological communities, these conclusions might have led to a final word in the “complexity-stability paradox”.

In our work Disentangling the effect of hybrid interactions and of the constant effort hypothesis on ecological community stability, published Early View in Oikos, we show that this is not the case. Indeed, we proved that mixing of mutualistic and predator-prey interaction types does not stabilize the community dynamics and we demonstrate that a positive correlation between complexity and stability is observed only if  species interact so that generalist species (the ones with several “partners”) interact very weakly (in terms of intensity) with respect to specialist species (which have only few partners). We also show that the main findings presented in Mougi and Kondoh work arise as an artifact of the peculiar rescaling of the interaction strengths they imposed. Indeed, using their methodology, the very same effect of ecosystem stabilization may be obtained for generic random ecological networks.

In conclusion, the mismatch between theoretical results and empirical evidences on the stability of ecological community is still there also for communities with a mixing of interaction types, and the “complexity-stability” paradox is still alive. Our work suggest that complexity and stability may be reconciled if a particular scaling of the interactions strength with the species degrees (number of resources) exists, but further studies and experimental evidences are still needed to better understand the role of interaction strengths in real ecological communities.

Samir Suweis, Jacopo Grilli,  Amos Maritan

Posted by: oikosasa | January 2, 2014

Monsterciliates as pac-man predators

A sheep increasing 4 times in size, starting to eat competing rabbits! Wow, that would be something! And it’s almost true, at least in the ciliate world! Find out more in the new Early View paper “Trait-mediated apparent competition in an intraguild predator–prey system” by Aabir Banerji and Peter J. Morin. Here’s their short version of the paper:

This investigation stemmed from our earlier work on the inducible trophic polymorphism (ITP) of Tetrahymena vorax.  In the presence of competing ciliates, individuals of T. vorax (starting as small, pear-shaped bacterivores) can completely reconstruct their cytoskeletons and increase their size to up to four times what it was before, becoming spherical predators capable of rapidly phagocytizing their competitors. This transformation occurs within six hours and is completely reversible.  In the figure below, the red arrow points to the cytopharynx (“mouth”) of the predatory morph.

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Though there are several real-life ITPs among macroscopic taxa that are roughly analogous to that of T. vorax, I find the fictional example shown below to be slightly more accurate (and fun to present).

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While attempting to see which prey we could rear T. vorax on of the ones we had in-stock at our lab, we noticed that T. vorax seemed to get bigger when fed bigger prey.  This is a pattern that has been observed in various other ciliate predators (and a few macroscopic predators), as well.  I was dying to call it “chasmatectasis” (from the Greek words for “gape” and “stretching”) – a term inspired by the way one of my friends in the medical profession had described the phenomenon of competitive eating: “self-induced gastrectasis.”  (Luckily, my labmates talked me out of coining lame phrases at this point.) 

What we really wanted to know was whether this phenomenon could give rise to a novel form of apparent competition (one that was trait-mediated, rather than density-mediated).  Conceptually, this would be like what happens in the Pac-Man video game – eating large prey items allows the predator to eat things it normally would not be able to eat.

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As it turns out, it can.

Posted by: oikosasa | December 30, 2013

Frugivore bird response to habitat loss and plant invasions

In subtropical and tropical forests up to 90% of woody plant species depend on fruit eating animals for the dispersal of their seeds. Birds are the most diverse and abundant animal group that acts as seed dispersers. Yet, many birds are threatened by the ongoing deforestation and the introduction of alien invasive (non-native and ecosystem-transforming) plant species. It remains a challenge for ecologists to predict how different frugivorous bird species respond to these environmental changes with ultimate consequence for the dispersal service they provide.

Fig 1 Large, undisturbed subtropical forests nowadays are generally confined to protected areas and gorges. On the plains forest extent is heavily reduced by intensive sugar cane farming.

Fig 1 Large, undisturbed subtropical forests nowadays are generally confined to protected areas and gorges. On the plains forest extent is heavily reduced by intensive sugar cane farming.

Factors that may drive bird responses to habitat disturbance comprise different dependencies on forested habitat and fruits as resources. Whereas forests specialists only occur in large, undisturbed forests, forest generalists often prevail in smaller fragments, and forest visitors generally dwell in open habitat such as grassland. Similarly, obligate frugivores exclusively feed on fruits to meet their dietary demands, whereas partial frugivores supplement their diets with insects or floral nectar, and opportunistic frugivores only rarely pick some of their favorite fruits.

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Fig 2 Forest island within sugar cane. Forest specialists and specialized frugivores are practically absent from such islands.

In our study “Guild-specific shifts in visitation rates of frugivores with habitat loss and plant invasion”, now on Early View in Oikos, we investigated whether changes in visitation rates of bird species (to plants for foraging on fruits) with forest loss and plant invasion can be predicted by their different dependencies on forested habitat and fruits as resources. To do so, we conducted extensive observations of plant-frugivore interactions in a subtropical South African forest landscape. These forests are highly diverse, and more than 700 bird species can be found in the region! However, South African forests are also under increasing pressure from intensive agriculture and urban sprawl, and many invasive plant species have replaced the natural vegetation. Fieldwork was fun but could be tough ­– sometimes we observed no visitor in 18-h of observation! Further, we wore military-style ‘ghillie suits’ for camouflage, a very effective way to hide in dense vegetation and minimize disturbance of birds. However, a woolen suit is a rather poor choice in South African summer…

Fig 3 Trumpeter hornbills (Bycanistes bucinator) are among the largest avian frugivores in South Africa. This individual feeds on fruits of Ficus glumosa.

Fig 3 Trumpeter hornbills (Bycanistes bucinator) are among the largest avian frugivores in South Africa. This individual feeds on fruits of Ficus glumosa.

Fig 5 Speckled mousebirds (Colius striatus) are generalized frugivores which are able to persist in a wide array of differently disturbed habitats. Unfortunately, few fruits on this Tassel-berry (Antidemsa venosum) shrub are fully ripe yet.

Fig 5 Speckled mousebirds (Colius striatus) are generalized frugivores which are able to persist in a wide array of differently disturbed habitats. Unfortunately, few fruits on this Tassel-berry (Antidemsa venosum) shrub are fully ripe yet.

Still, the African bird life was totally worth it, and we found highly interesting results. As expected forest specialists were most negatively affected by habitat loss. However, interestingly, obligate frugivores were overall least affected by habitat loss and plant invasion. Fully depending on fruits requires a generalized fruit choice, which seems to make obligate frugivores more robust to changes in habitat conditions. In contrast, visitation of partial and opportunistic frugivores declined – a pattern that can be explained by the comparably more specialized or ‘picky’ foraging behavior of non-obligate frugivores. Specialist foragers were particularly rare when high degrees of habitat loss and plant invasion interacted in synergy.

Fig 4 Testing the ghillie suit in a farmhouse garden. When hiding in even denser vegetation, the observer becomes practically invisible to the avian (and human) eye.

Fig 4 Testing the ghillie suit in a farmhouse garden. When hiding in even denser vegetation, the observer becomes practically invisible to the avian (and human) eye.

In summary, our study shows that forest loss and plant invasion may especially negatively affect forest specialists and specialized frugivores. This is worrying, as it is those ‘unusual’ species, which by their diverging ecological and behavioral differences from generalized species, considerably contribute to the astonishing diversity of subtropical and tropical forests. Not to forget that most often, they are also wonderful to look at.

Fig 6 These fruits of invasive Bugweed (Solanum mauritianum) show clear marks of pecking frugivores. The plant flowers (background) and fruits at the same time and is able to do so year-round, a significant advantage over many native plant species.

Fig 6 These fruits of invasive Bugweed (Solanum mauritianum) show clear marks of pecking frugivores. The plant flowers (background) and fruits at the same time and is able to do so year-round, a significant advantage over many native plant species.

Ingo Grass, Dana G. Berens and Nina Farwig

Posted by: oikosasa | December 20, 2013

Top-cited Oikospaper

Congratulations, Jeff Ollerton, Rachael Winfree and Sam Tarrant for passing 100 citations for their paper “How many flowering plants are pollinated by animals?”, published in Oikos in March 2011.

But Jeff, how did you come up with the idea for the paper?

Jeff in TanzaniaThe idea for the paper arose when I was trying to find a solid figure in the literature for the proportion of plants that are biotically pollinated.  It’s an important starting point for any argument about the importance of conserving pollinators, I think: policy makers like to be able to present numbers.   Lots of figures were being quoted, from a range of sources, but once you follow the reference chain back through the papers that cite them you find that numbers which are cited as solid facts disappear into speculation and guestimates.  Like many of the simple and obvious questions, the assumption is that we “know” the answer.  That’s no basis for science-informed conservation policy, but I suspect that it happens all too frequently.

Did you know that the paper would be cited?

To be honest, yes, because a lot of studies and papers are now focussing on the ecology and conservation of plant-pollinator interactions, and our paper provides an initial rationale for why it is important to study them.  But I didn’t appreciate quite how well cited it would be, that certainly took us by surprise:  over 30 citations per year is a high rate in ecology!

Visit Jeff’s blogg:

 

Posted by: oikosasa | December 17, 2013

Hurray! We have a new cover!

We are very happy to present our cover for 2014! As you might recall, we had a photo competition to find a  nice photo showing ecology in action. And we have a winner!

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Congratualtions Prof. Erik Svensson, Lund to the fantastic photo of emerald damselflies!

Here, Erik describes the photo:

The emerald damselfly (Lestes sponsa) is a common insect that is often found mating and ovipositing in the vegetation close to the small ponds where the larvae will later develop. Mating starts with the male clasping a female on her prothorax and so-called “tandem formation”, before sperm transfer. here are two couples (males are green, females are brown) that have formed tandems, and by accident, a chain of our has been formed. The picture was taken in the province of Skåne, (Southern Sweden) in the summer of 2010.

Posted by: oikosasa | December 13, 2013

Joint effects of predator and parasite on prey stress levels

We generally focus on either predation or parasitism. But what happens when we look at the combined effects of the two? Find out in the new Early View paper in Oikos: “Predators and trematode parasites jointly affect larval anuran functional traits and corticosterone levels” by John A. Marino Jr and co-workers. Read their summary here:

In addition to directly causing death, predators can have a range of effects on prey that detect their presence, including altered growth, behavior, and stress hormone levels. These effects may strongly affect how potential prey animals interact with other species. For instance, predator presence may affect interactions between prey species and parasites, which could change the effects of parasite infection on hosts. In our study, we examined how larval dragonfly predators affect the interaction between tadpoles (wood frogs and green frogs) and their parasites in a series of aquaria experiments.

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We excluded direct predation by only exposing tadpoles to predator chemical cue (i.e., water from containers holding predators), which has effects on tadpoles similar to actual predator presence. The parasites were a common group of trematodes (flatworms) known as echinostomes, which infect the kidneys of tadpoles. We examined how predator cue affected the response of tadpoles from their first detection of parasite presence to after infection. We found that parasite infection reduced tadpole activity, growth, and survival, and predator cue reduced activity and growth. We also found that the effects of parasites on tadpole behavior, stress hormones, body shape, and development depended on the presence of predators. These effects would be hard to predict by only considering predator and parasite effects separately, which is the case in most studies. Our findings thus emphasize the importance of considering the effects of parasites and predators jointly. The effects we observed are likely important in natural populations and may have important consequences for amphibian conservation. Echinostomes are more abundant near human activities (e.g., agriculture, urbanization), so that their joint effects with other stressors of amphibians, such as predators, are important to understand.

Photo: Ariel Heldt

Posted by: oikosasa | December 3, 2013

Editor’s Choice December

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Science makes progress by applying an experimental approach. This holds in ecology and many of us setup experiments to test the impact of stressors on diversity changes all levels of biological organisation, or how certain treatments affect specific ecological and evolutionary mechanisms. While there have been calls to use experimental approaches to understand eco-evolutionary responses to global change, such approaches often fail because of oversimplification of the real world. On the other side, such approaches allow true replication, a principle condition in science; conditions hardly met using natural experiments. In the forum paper of this month, Janneke HilleRisLambers and colleagues outline that we should embrace ongoing global change (from a scientific point of view only though) as they provide us ‘accidental experiments’ to gain fundamental insight into ecological and evolutionary processes. This is especially true when they result in perturbations that are large or long in duration and difficult or unethical to impose experimentally. While we all agree that such an approach will never replace the experimental method, it is clear that such accidental experiments provide considerable advantages relative to more traditional approaches and are able to provide fundamental scientific insights. HilleRisLambers  et al. provide a forum paper in the best Oikos tradition. A must read!

Synthesis of the paper, as outlined by the authors:

Humans have an increasingly large impact on the planet. In response, ecologists and evolutionary biologists are dedicating increasing scientific attention to global change, largely with studies documenting biological effects and testing strategies to avoid or reverse negative impacts. In this article, we analyze global change from a different perspective, and suggest that human impacts on the environment also serve as valuable ‘accidental experiments’ that can provide fundamental scientific insight. We highlight and synthesize examples of studies taking this approach, and give guidance for gaining future insights from these unfortunate ‘accidental experiments’.

We are also happy to highlight Coreen Forbes’ and Edd Hammill’s research paper as editor’s choice. By making use of an excellent multiple generations dataset, the authors demonstrate the importance of non-consumptive effects on food web dynamics. While the impact of such effects have been demonstrated in simple experiments, the authors moved some steps further and installed experimental microbial communities to seek generality of the available theory and experimental evidence. I would argue that accidental experiments would never allow for insights generated by experimental approaches like these, because, as expected by many, such community level effects appear to be highly context dependent. This context-dependency has here been identified and tested: heterotrophic species that rely on active fouraging to acquire resources are more affected by the presence of predators than other species, especially under conditions of darkness. In short, the paper provides novel, highly relevant insights on community functioning, highlights an unexpected impact of a largely neglected, but overall present abiotic condition by using creative experimental approaches of communities under equilibrium conditions. Clearly work that advances community ecology by targeting mechanisms rather than patterns!

Synthesis of the paper, as outlined by the authors:

Predators affect prey through consumptive and non-consumptive effects (NCEs) such as alterations to prey behaviour, morphology, and life history. However, predators and prey do not exist in isolated pairs, but in complex communities where they interact with many other species. Using a long term study (>10 predator generations), we show that predator NCEs alone can alter community structure under conditions of darkness, but not in a 12h:12h light:dark cycle. Our results demonstrate for the first time that although the community-level consequences of predator NCEs may be dramatic, they depend upon the abiotic conditions of the ecosystem.

I found little to disagree with in the post by Lortie – all very worthy points. I am also very much for placing much emphasis on novelty/creativity/newness. Where we differ, I think, is in the amount of confidence and trust we place upon editors. Having been an editor for many years in several journals in our field, and having been an “author” and a colleague for even longer, I have developed a conviction that the system employed by many journals (where the editorial machinery rates newness without “external” input) is sensitive and imprecise. I was trying to make the point in the TREE article that this is very problematic.

“Newness” is this golden but elusive aspect of a work that, even though we all know exactly what it is, remains hard to define and pin down. I think that everyone that has read Pirsig’s “Zen and the noble art…”, who makes much the same point about “quality”, will be able to relate to this. I am much less optimistic than you are that these qualities allow themselves to be explicitly and objectively defined in a manner which would make them operationally very useful. For this reason, I think that creativity or newness needs to be assessed by (1) initiated, educated and wise readers and (2) several such readers. That is the essence of my point.

Now, in the best of all worlds, we would elect editors that are capable of serving as benevolent and wise dictators who fairly and correctly assess the newness of all submitted manuscripts and rules accordingly. This would certainly improve science and save us all a lot of work. Unfortunately, Dr. Pangloss was, I fear, wrong.

Posted by: oikosasa | November 29, 2013

No more calls for the end of invasion biology?

Is invasion biology needed or not? In the Forum paper “A call for an end to calls for the end of invasion biology” by Daniel Simberloff and Jean Vitule continues the discussion, which Valery et al contributed too recently in Oikos. Below is the author’s summary of the paper:

The flood of damaging invasions by introduced species continues, with weekly reports on major invaders, such as Old World pigs in North and South America, Asian hornets in Europe, Asian ladybeetles in North America, Europe, and Africa, African grasses in the Americas and Hawaii, and African catfish in China and Brazil.  This rearrangement of global biogeography attracts public attention primarily when an invader does something dramatic and obvious that annoys humans, as when pigs ravage crops, hornets deliver painful stings, ladybeetles foul wine, grasses foster devastating fires, and catfish invade protected areas preying on native species used in traditional fisheries.  However, the myriad subtler impacts on individual species and on entire ecosystems exact a toll on human interests that is just beginning to be understood as the rapidly growing young science of invasion biology elucidates ever more mechanisms and outcomes of invasions.

The picture is not wholly bleak, however, as scientists develop means of preventing and managing invasions apace with understanding of the scope and scale of their consequences.  A plethora of mechanisms have been brought to bear successfully on damaging invasions, including biological control, chemical herbicides and pesticides, mechanical and physical measures, and a variety of clever specialized approaches tailored to the idiosyncrasies of particular invaders.  Notable recent advances include the use of pheromones to manage invasive sea lampreys in the North American Great Lakes, biological control insects, mechanical methods, chemicals, and inventive use of fire to cut back Australian paperbark in Florida, toxic microbeads to lower zebra mussel densities in water facilities, quick use of chemicals to eradicate infestations of an Australia marine algae in California and a Caribbean mussel in Australia, and eradication of introduced rats by poison baits on islands of ever-increasing size around the world.

Notable in these successes is that, in many cases, researchers did not wait to see what the impacts of the invaders would be, but acted quickly (e.g., the examples of the alga in California and the mussel in Australia).  Almost certainly the opportunity for eradication would have been lost had the scientists focused solely on impacts, rather than on the origin of the invader.  Another important point is that many of these successes (e.g., the paperbark in Florida, the sea lamprey in the Great Lakes, and many island rat populations) were achieved against longstanding invaders that had previously proven intractable.   Also, removal of well established invaders in these cases did not lead to unexpected harmful effects on any native species.

Finally, a few native species, particularly in the wake of various human impacts, behave like invasive non-native species, but harmful impact are far more likely for non-native than for native species.  The argument that fighting invaders and the traditional restoration focus on fostering native species are futile endeavors is contradicted by growing successes in restoration and invasion management.  

Figure 1. Jean Vitule holding a wild-caught African catifish Clarias gariepinus from an Atlanctica forest protected area in Guaraguaçu River, Brazil. Picture taken by Simone Umbria.

Figure 1. Jean Vitule holding a wild-caught African catifish Clarias gariepinus from an Atlanctica forest protected area in Guaraguaçu River, Brazil. Picture taken by Simone Umbria.

Posted by: oikosasa | November 26, 2013

The importance of territorial behavior in ecological networks

To eat or to be eaten-  that’s not always what matters. The importance of non-trophic interactions, such as territorial behavior, in ecological networks, communities and ecosystem studies is dealt with in the new Early View paper “Territorial ants depress plant growth through cascading non-trophic effects in an alpine meadow” by Chuan Zhao and colleagues. Below, you find a summary of the study:

All species are embedded in ecological networks, which are composed of both trophic and non-trophic interactions.  Trophic interactions are well recognized as a major force structuring ecological communities and regulating ecosystem functions.  Meanwhile, although non-trophic territorial interactions between animals have long fascinated behavioral ecologists, their potentially cascading ecosystem-level effects have been largely overlooked.

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In our manuscript, we provide one of the first demonstrations of a cascading effect of territorial interactions and, to our knowledge, the very first within the context of a detritus food web. Specifically, in a Tibetan alpine meadow, we experimentally investigated the non-trophic interaction between territorial ants and members of a dung decomposer community, as well as the ecosystem consequences of this interaction. We discovered that ants significantly decreased the abundance of coprophagous beetles and hence triggered a cascade whereby dung removal rates and soil nitrogen concentrations were reduced, ultimately decreasing aboveground plant biomass.

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Our results show that animal territorial behavior, which is pervasive across animal taxa and ecosystems, can have strong cascading effects and therefore should be explicitly considered in models and experiments linking community structure and ecosystem functioning. Moreover, the results reveal a mechanism through which non-trophic interactions can link animals that do not otherwise interact through more widely studied forms (competition, predation or facilitation).

Posted by: cjlortie | November 23, 2013

Chasing the white rabbit: novelty as a filter for editors

A recent spotlight paper in Trends in Ecology & Evolution by Goran Arnqvist challenged the notion that editors should use novelty as means to review submissions. This is a very useful contribution to the dialog associated with evolving peer review. It is particularly important for Oikos. A significant aspect of Oikos publications is novel synthesis as described in the mission statement. Consequently, the ability to assess novelty is a necessary skill for editors. In a commentary on this topic, I propose that a solution to this apparent dilemma is to shift the focus from seeking novelty to seeking creativity. This may seem like a subtle semantic shift, but creativity research is a well articulated discipline and is best defined as the combination of novel + useful. I suspect most Oikos editors use some working definition similar to this conceptual framework already.

Chasing creativity may be like chasing the white rabbit in Alice’s Adventures in Wonderland, but we are already down the rabbit hole of peer review and formalizing and discussing how we evaluate the work of others is a positive step forward.

400px-Down_the_Rabbit_Hole

Posted by: oikosasa | November 22, 2013

The typical ecological answer – it depends

Which species is best for their host marsh cordgrass? Fiddler crab or mussel? The answer is – it depends. As often, both in ecology and everyday life! Read more in the new Early View paper “Independent and interactive effects of two facilitators on their habitat-providing host plant, Spartina alterniflora” by A. Randall Hughes and colleagues. Below is a short summary of the study: And don’t miss the video in the end!

From a distance, salt marshes appear dominated by one (or maybe a few) plant species, such as marsh cordgrass Spartina alterniflora. 

spartina_salt_marsh

However, there are also many animals residing in the marsh, and prior research has demonstrated that two of these animal species, fiddler crabs (Uca sp.) and ribbed mussels (Geukensia demissa) facilitate the growth and production of cordgrass.  Fiddler crabs create burrows that increase oxygen in the sediment, reducing stress on cordgrass roots.  The fiddler crabs also aerate the sediment during their feeding, and they excrete nutrients that can be utilized by the plants.  Mussels aren’t quite as charismatic as fiddler crabs, but they settle around stems of cordgrass, and the byssal threads that they use to attach to one another and to the sediment can help prevent erosion.  In addition, they excrete nutrients and other organic material as a byproduct of their filter-feeding, and the plants take advantage of these nutrients.

fiddlers_in_marsh

 So who is MORE beneficial for cordgrass, mussels or fiddler crabs?  And is having both species present better than just having one?  Our study suggests that as with much in ecology – it depends.  For one, it depends on what you measure.  If you look at the number of cordgrass stems, then fiddler crabs are the better facilitator – cordgrass with fiddler crabs has higher densities than cordgrass without fiddler crabs, regardless of whether you have mussels or not.  But if you look at plant height (which is correlated with biomass), then mussels are the better facilitator, but only when fiddlers aren’t around.  It also depends on cordgrass genetic identity: some genotypes respond more strongly to the presence of facilitators than others. In the end, the more responses (and genotypes) you include, the greater the benefit of having both facilitator species. 

fiddler_close-up

Over the course of this study, Althea (my co-author and graduate student) noticed high mussel densities in and around sea lavendar (Limonium carolinianum) plants.  She is now exploring this relationship and its implications for our understanding of facilitation more generally.   A good example of how there are always more questions than answers…

 Video link -

http://www.youtube.com/watch?feature=player_embedded&v=htOwL70LKyw

 

Video caption: – This video was produced by WFSU-TV for the In the Grass, On the Reef project.  In the Grass, On the Reef is funded by the National Science Foundation.

 

Photo credits: R. Hughes

Posted by: oikosasa | November 20, 2013

New Preprint server

Is preprint here to stay? And will it decrease the burden of reviewing?

We’ve seen Peerage of Science, F1000 research and PeerJ. And here’s the next preprint server, for biological manuscripts only, BioRxiv, which you can read more about on Science Insider:

http://news.sciencemag.org/biology/2013/11/new-preprint-server-aims-be-biologists-answer-physicists-arxiv

A problem might be that the journal targeted for final submission might not allow submissions of manuscripts that have already been shared online.

We are happy to announce that Oikos welcomes submissions of manuscripts that have been “published” on those preprint servers.

Here is a list of journal policies in the matter:

http://en.wikipedia.org/wiki/List_of_academic_journals_by_preprint_policy

So will you share your next manuscript online to get comments during the writing process?

Posted by: oikosasa | November 15, 2013

New aspects of land use impacts on biodiversity

In the new Oikos Early View paper, “Inferring temporal shifts in landuse intensity from functional response traits and functional diversity patterns: a study of Scotland’s mach air grassland”, Rob J.Lewis and colleagues explore how land use changes affect community assembly processes. Here’s Rob’s summary of paper:

There is a growing consensus among ecologists that a trait based view on species community composition may far outweigh the utility of one solely centred on taxonomic composition in explaining the structure and function of ecological communities. Such a shift in focus has resulted in a considerable increase in the number of scientific studies examining links between individual traits and the environment. In the realm of plant ecology, particular traits have been shown to respond consistently to changes in the environment. Collectively, these traits are termed plant functional response traits and are increasingly used to explain how plant functional composition responds to environmental change, particularly along environmental gradients of disturbance.

In this study, we utilise an a priori knowledge of how plant functional response traits linked to disturbances such as grazing intensity, agricultural intensification and land-use abandonment to infer land-use drivers of temporal change (over ca. 30 years). We also adopt relatively new metrics to derive composite indices of functional diversity to investigate shifts in community assembly mechanisms over time. Moreover our approach was applied to a national-scale temporal vegetation dataset of a globally rare semi natural grassland termed ‘Machair’, an extremely complex, species-rich, costal dune plain of ecological and cultural importance

Baseline data was derived from the Scottish Coastal Survey first collated in the mid 1970’s by the Nature Conservancy Council (NCC), with the aim to identify ecologically important and sensitive areas of Scotland’s soft coast (i.e. low lying coastal areas composed of sand, shingle or mud). Records included data on plants, habitats, environment and land-use of circa 4000 vegetation plots. As part of the lead author’s PhD thesis, we performed a re-survey of this dataset between 2009 and 2010, focusing specifically on sites known to include Machair, providing temporal data for most of the western and northern seaboard of Scotland.

This paper, the first of a series that make use of this unique dataset for investigating temporal patterns of change, discusses the observed shifts in functional traits and functional diversity indices over time, the potential causations driving these relative to land-use practices on the Machair, and the utility of our methods for inferring temporal drivers of functional compositional change.

R_Lewis_Blog_Image

Posted by: cjlortie | November 12, 2013

Upping your theory game by Samuel M. Scheiner

Recently I published an analysis of the extent to which the ecological literature engages with theory (http://onlinelibrary.wiley.com/doi/10.1111/ele.12196/abstract). One part of that analysis was a comparison of current journals. Among the ecology journals, Oikos scored the highest with 73% of the papers in the 2012 June and July issues including some aspect of theory development or testing. But we can all do better. Here are some ways to increase the theory engagement of your papers.

First ask yourself, “What theory does my paper relate to?” Even if your paper is a description of some system, that description must relate to the facts that underpin some theory. Theories rely on generalizations. Does this particular instance help strengthen a generalization? Does it dispute a generalization? Is the state of knowledge such that generalizations are uncertain? If so, how does this paper reduce that uncertainty? Then make that theory and those generalizations guideposts for the entire paper.

But you say, “There is no formal theory for this question, just a general understanding.” That general understanding is the theory, it simply lacks formalization. In the parlance of the theory structure presented by Mike Willig and myself, no constitutive theory exists. Here is an opportunity for you to create one. Formalizing a constitutive theory is not difficult. For examples of how to do this, see our book (Scheiner and Willig. 2011. The Theory of Ecology. University of Chicago Press). If there are already numerous models relating to the topic, it is an exercise in finding their common threads. That is the process that we went through with our first constitutive theory (Scheiner and Willig. 2005. Am. Nat. 166:458-469). For more nascent fields, you may have to work a bit harder to discern those threads. In the end you will have a list of rules and generalization (“propositions” in our terminology) against which to compare your data.

As a reviewer of papers, ask if a paper engages in theory right at the beginning. My tally of “no theory” papers included many for which formal theories exist, but no explicit connection was made. Make sure that this happens. If the introduction of the paper does not explicitly name a theory, insist that it do so. We should be asking more of ourselves. Ecology is a mature discipline rich in theories. Our science will only be strengthened by all of us doing more to engage with theory and insisting that our colleagues do likewise.

Posted by: oikosasa | November 12, 2013

Editor’s choice November 3.0

Last week, EiC Chris Lortie presented the editor’s choice papers for the November issue. Below you find the nice figure and table from one of them, “Dispersal and species’ responses to climate change”, by Travis et al. And remember, Editor’s choice papers are freely available online throughout the month!

Table1_399b

Table 1: Effects of climate change on individual dispersal. Climate change is predicted to lead to lower windspeeds (A), higher temperatures (B), increased frequency of storms (C), flooding (D), reduced snow cover (E), and changed rainfall (F) (1, 2). Each of these climatic factors has been shown to affect dispersal in a range of organisms, either through a direct impact on the individual during dispersal, or indirectly by altering the biophysical environment or the state of the dispersing organism. Key empirical examples of these effects are described with the arrow (    decrease;     increase) describing how predicted changes in specific climatic factors would alter the propensity to emigrate or the distance dispersed during transfer.

Figure1_399b

Figure 3: Dispersal will be the heart of a new generation of process-based models developed to predict, and inform the management of, species’ responses to environmental change. By incorporating dispersal together with an explicit representation of population dynamics, models will become much better able to simulate the spatio-temporal dynamics of species under alternative future climate and land-use scenarios. To date, most projections of biodiversity responses to climate change have been made using all or nothing dispersal with fewer examples of nearest-neighbour dispersal or statistical dispersal kernels. While more detailed mechanistic dispersal models have been developed both for animal and plant dispersal, they have yet to be used extensively in the climate change field. In part this is due to the substantial challenges faced with these more sophisticated models, both in terms of the data needs for parameterisation and the greater computation needs of these more complex approaches. We argue that incorporating greater realism in the dispersal process will result in improved predictive capability, particularly when there are likely to be synergistic impacts of climate and land use change.

[Image credits: Corine Land Cover (land cover map); Wordclim (climate map); James Bullock (bustard); María Triviño (observed and predicted maps of bustard distribution)]

Posted by: oikosasa | November 8, 2013

Reminder: Photo competition- Oikos cover 2014

A few days left to submit your ecology-photo!

Will your photo be on the Oikos cover 2014?

We seek photos illustrating the Oikos’ goal of Synthesising Ecology or demonstrating ecology in action (e.g. processes or interactions), not only a single organism or a landscape.

Please send your photos together with the  oikos-photo-competition-form14 to oikos@oikosoffice.lu.se, with Photo competetion as subject, before November 10th 2013. The winner will be awarded a book price from Amazon for a value of 100 Euro. The winning photo will be at the cover of all issues of Oikos from during 2014.

Competition Rules:

Entries must be digital images, submitted electronically, in jpg or tiff-format. Images must be available in 300 ppi.

Digital enhancements must be kept to a minimum and must be declared. Both the original and the enhanced image must be submitted.

File names must include appplicant’s surname.

Photos must be accompanied by an entry form that describes illustrated species and scenes. Download the oikos-photo-competition-form14

A prize committee consisting of Managing Editor, Editor in Chief, deputy editors, Technical Editor of Oikos and the Director of the Oikos Editorial Office, will judge which photo that best suits our requests. The decision by the committee is final.

All submissions will be entered under a Creative Commons License and will be displayed on Oikos webpage and social media and may be used  for commercial purposes. Download Creative Commons License here.

Oikos takes no responsibility for submitted images being lost, damaged or dealyed.

How herbivores and nutrient interact in grassland communities is studied in the early View paper “Multiple nutrients and herbivores interact to govern diversity, productivity, composition, and infection in a successional grassland” by Elizabeth T. Borer and co-workers. Here’s Elizabeth’s summary of the paper:

borer-etal-oikos-concept-fig

We have all heard about the health benefits of a balanced diet, and it turns out that nutritional balance matters in ecosystems, too. While most research examining nutrient effects on ecosystems has focused on one or two nutrients, such as nitrogen and phosphorus, humans are concurrently changing the supply rates and ratios of many different nutrients, creating the possibility for complex effects on ecosystems and the services they provide.  We found that the ratio of nitrogen to phosphorus supplied to a grassland ecosystem had larger impacts on infection by a common crop disease than any single major nutrient alone. Grassland net production increased with nitrogen fertilization, but consumption of plants by a common grassland herbivore, the pocket gopher, caused net grassland production to decline with fertilization. Single factor studies would not have uncovered these and other relationships even though such relationships are critical for effective predictions of biodiversity and ecosystem functioning in a world in which human activities are simultaneously changing herbivore abundance and the relative supply of many growth-limiting nutrients.

sedg-oblique-20030326-small

Posted by: cjlortie | October 29, 2013

Editor’s Choice November: Indirect interactions

Indirect interactions are one of my current favorite topics. So fascinating, so elusive, simple in theory, but easily construed. This was the second editor’s choice for November:

Alexander, M. E., Dick, J. T. A. and O’Connor, N. E. 2013. Trait-mediated indirect interactions in a marine intertidal system as quantified by functional responses. – Oikos 122: 1521-1531.

doi: 10.1111/j.1600-0706.2013.00472.x

Trait-mediated indirect interactions are tested in a highly tractable system in this study. However, a very elegant experimental design was executed to explore whether habitat complexity was important to the functional response expressed by predators. Three species were used in total (2 predators and 1 prey species) and experimental arenas were used (Fig 1). Diet cues and responses to the other species were examined in petri dishes with stones glued to the bottom.  Very clever! I would love to see a real photo of the design or videos of the various activity levels reported.

Novel synthesis
This study was an example of novel synthesis for the following reasons.
The design was superb.
The ideas, terms (such as density-mediated indirect interactions versus trait mediated), and predictions were extremely well developed and very precise.
Simple versus complex habitats was tested thereby addressing a major and ongoing theme of context dependence in ecology and evolution.
Density and indirect interactions are well modeled in the study.

Ecologically, the findings were significant in that habitat complexity is shown to mediate population stability. Super simple spoiler: in simple habitats, trait-mediated indirect interactions may destabilize prey populations whilst in complex habitats regulation of intermediate consumers may promote prey stability. Fantastic. I wonder how we could apply this approach to terrestrial systems.

Amphipoda (not actual size):

Bathyporeiapilosaweb

 

Sample petri dish arenas in general:

mold2

Posted by: cjlortie | October 29, 2013

Editor’s choice November: Dispersal and climate change.

Will climate change ever have positive impacts :) In many respects, climate change and invasive species both challenge our notions of community assembly and the relative importance of various drivers in structuring both populations and communities. For the first editor’s choice for November, we selected the following paper.

Travis, J. M. J., Delgado, M., Bocedi, G., Baguette, M., Bartoń, K., Bonte, D., Boulangeat, I., Hodgson, J. A., Kubisch, A., Penteriani, V., Saastamoinen, M., Stevens, V. M. and Bullock, J. M. 2013. Dispersal and species’ responses to climate change. – Oikos 122: 1532-1540.

doi: 10.1111/j.1600-0706.2013.00399.x

Rationale & novel synthesis
Dispersal describes a fascinating set of processes in ecology and evolution. However, the semantics are not that well articulated. In this article, the terminology and scope of dispersal is well developed. Importantly, the capacity for dispersal to evolve under climate is examined and the reciprocal concept, how dispersal should be included in predictive models is also summarized. The direct and indirect causes of changed dispersal are summarized with an excellent graphic, and the predicted impacts on emigration and transfer phases are provided separately. A central role for dispersal is proposed for considering the climate change versus land use drivers on the realized population dynamics. I like this idea. I am not an dispersal expert at the scale but this seemed like a very reasonable,if not challenging, novel conceptual model.

Five priority areas for conservation are identified.
1. Protocols must be developed to gather/aggregate high-res datasets on dispersal at all scales.
2. Mechanistic movement models and more realistic models in general must now be used.
3. Predictive models must now included more nuanced handling of within species variation.
4. Include relationships between evolution and dispersal in models when examining trait sets (and plasticity, selection processes, etc).
5. Use models to most effectively intervene in managed dispersal processes.

OLYMPUS DIGITAL CAMERA

Posted by: oikosasa | October 28, 2013

Measuring the strength of trade-offs

A new method to measure the strength of trade-offs is presented and tested in the Early View paper “A standardized approach to estimate life history tradeoffs in evolutionary ecology” by Sandra Hamel and co-workers. Here’s Sandra’s summary of the paper:

A major goal of life-history studies is to understand how natural selection shapes individual fitness-related traits, such as growth, reproduction, and survival. So far, a large number of studies have demonstrated the occurrence of many trade-offs (e.g. number vs. size of offspring, age at first reproduction vs. longevity), but most researches have concentrated on detecting trade-offs – that is answering “yes” or “no” to the question “Is there a trade-off between trait A and trait B”. Although these studies are fundamental because they have provided substantial empirical evidence for the existence of trade-offs, they are somewhat limited. For instance, if we wish to understand how different life-history strategies evolve among different species, among populations of the same species, or among individuals of the same population, we need to be able to tell not only whether there is or not a trade-off, but most importantly what is the strength of this trade-off.

Measuring the strength of a trade-off would be highly valuable for determining its relative importance. For example, to determine whether the trade-off between current and future reproduction is stronger in shorter- vs. longer-lived species, we need to measure the strength of this trade-off in different species. Within a single species, we might also want to determine whether trade-offs among growth and survival traits are stronger than trade-offs among growth and reproductive traits, which could allow us to better understand where the strongest selection pressures occur.

Our paper therefore presents a method to measure the strength of trade-offs. Although some methods have been used previously to quantify trade-offs, these methods cannot be applied with respect to binary traits – that is traits usually described by “yes/no”. Indeed, analyses of binary data present many analytical issues and thereby are more complex and often more limited compared with other types of data. Nevertheless, binary traits are central in life histories (e.g. probability of reproduction, nesting success, offspring survival), and so we need a method that can be applied to any type of traits to be able to compare the importance of different life-history trade-offs. Our paper provides such a standardized approach, which also accounts for the confounding effects of both environmental variation in resource availability and individual heterogeneity.

We illustrate the large potential of our approach by applying our method to longitudinal data from roe deer and mountain goats. Out of seven trade-offs measured, the strongest was observed between current and future parturition in mountain goats, a capital breeder, whereas this trade-off did not occur and rather showed a weak positive effect in roe deer, an income breeder. Although the trade-offs presented are only a few examples in two species, they suggest that the between-species differences might result from different tactics of energy allocation to reproduction. Most importantly, these examples illustrate how our method can be used to compare the relative importance of different trade-offs, and how it opens the door to a deeper understanding of the evolution of life-history traits in free-ranging populations.

Mountain goat sucklingroe deer ecographie

The pictures represent the two species used in the examples. On one picture we have a 14 year-old mountain goat female nursing her kid. On the other picture we have a roe deer female that is being checked for pregnancy with an ultrasonic scanner seen in the background.

Posted by: oikosasa | October 25, 2013

Can plants make a decision?

Plants that make active decisions? Read more in the Early View paper “Informed dispersal in plants: Heterosperma pinnatum (Asteraceae) adjusts its dispersal mode to escape from competition and water stress” by Carlos Martorell and Marcella Martinez-Lopez. Here’s their summary of the paper:

We all know someone who has migrated to a wealthy country because social or economic conditions in her/his homeland are harsh. Among animals the same phenomenon occurs, sometimes taking the form of huge migrations away from areas that are seasonally adverse because they are too cold or too dry. But what about plants? We all know that plants can move from one place into another when they are seeds, but it would appear that they are unable of judging whether it is profitable to stay in their natal site or to migrate in search of a better place. To do so, plants, like animals, need to gather and process information about their environment. The small annual plant Heterosperma pinnatum does exactly so. When the environment in which it grows is too dry, it promotes the long-distance dispersal of its seeds. The same happens in crowded areas where competition for the available resources is strong. In this way, its descendants may find more favorable places to live in. The mechanism is quite simple: H. pinnatum produces two different kinds of fruit, one that has hooks that become attached to animal fur and thus can travel very large distances, and another kind that lacks dispersal structures and thus remains in the close vicinity of the mother plant. By regulating the proportion of each type of fruit depending on environmental conditions, this plant is able to decide whether its descendants will continue to exploit the local resources or else face the risks of long-distance travel in search for a place where they may have better chances to survive and reproduce.

Different fruits of Heterosperma pinnatum. Left: an unawned fruit of the type that usually remains some 10–20 cm from the mother plant. Right: a fruit with awns on top of a long beak that projects away from the mother plant. When an animal passes by, the exposed awns become attached to its fur and the fruit is dispersed over a long distance. Middle: an intermediate fruit with awns but no beak. Photo: LFVV Boullosa.

Different fruits of Heterosperma pinnatum. Left: an unawned fruit of the type that usually remains some 10–20 cm from the mother plant. Right: a fruit with awns on top of a long beak that projects away from the mother plant. When an animal passes by, the exposed awns become attached to its fur and the fruit is dispersed over a long distance. Middle: an intermediate fruit with awns but no beak. Photo: LFVV Boullosa.

Posted by: oikosasa | October 22, 2013

Safer with close neighbors

Does new-density increase or decrease predation rate? Find out in the new Early View paper “Adaptive nest clustering and density-dependent nest survival in dabbling ducks” by Kevin M. Ringelman and co-workers. Here’s Kevin’s summary of the paper:

IMG_0421Many wildlife populations are regulated by density dependence: when populations become very large, survival and recruitment rates tend to decline.  In North American waterfowl, density dependence is often observed at continental scales, and nest predation has long been implicated as a key factor driving this pattern.  Predators may aggregate in areas of high nest density, and can reduce nest success to the point where it limits population growth.  However, despite extensive research on this topic, it remains unclear if and how nest density influences predation rates.  Part of this confusion may have arisen because previous studies have examined density-dependent predation at relatively large spatial and temporal scales.  To address this, we used three years of data on nest survival of two species of waterfowl, Mallards and Gadwall, to more fully explore the relationship between small-scale patterns of nest clustering and nest survival. 

IMG_0610

Throughout the season, we found that the distribution of nests was consistently clustered at small spatial scales (~50 – 400 m), especially for Mallard nests, and that this pattern was robust to yearly variation in nest density and the intensity of predation.  We also showed that nests within a cluster had lower predation rates, which runs counter to the general assumption that predators are attracted to areas of high nest density.  Because the predators at our study site probably only depredate duck nests incidentally, nesting a group could effectively dilute predation risk from predators that are “just passing through.”

IMG_2094-2029

Posted by: oikosasa | October 18, 2013

Crowding effects on indfidelity

How density effects reproductive success and extra pair-paternity is studied in the new Early View paper “Form, function and consequences of density dependence in a long-distance migratory bird” by Ann E. McKellar and co-workers. Below is Ann’s summary of the study:

The negative effects of an increasing population density on reproductive output have long been recognized in many animals, including migratory birds. As breeding density increases, territory sizes generally decrease, causing crowding and increasing neighbour-neighbour interactions, which can lead to decreases in rates of foraging and chick feeding, and increases in rates of nest predation. Such density-dependent processes can thus produce negative feedbacks which contribute to population regulation and the general stability of population size, since periods of high population density will reduce overall breeding success, and vice versa.

Moreover, population density can affect mating tactics. Rates of extra-pair copulations often increase with population density, thus providing an additional challenge to the reproductive fitness of males residing in dense areas.

Interestingly, the density dependence of demography and behaviour are rarely studied simultaneously. And yet such a holistic view is important because individual behaviours can influence population demographics, which can then feed back into the success of individual behaviours. These types of behavioural-demographic loops are no trivial matter, as modeling exercises have shown that they may influence the probability of population extinction.

We examined the density dependence of reproductive success and extra-pair paternity at a long-term study site of breeding American redstarts in Ontario, Canada. We found that greater breeding density was associated with reduced reproductive success, likely as a result of increased nest predation, and increased rates of extra-pair paternity. Overall, these findings contribute to a broader understanding of the selective pressures and regulatory mechanisms acting on migratory birds, from the individual up to the population level.

McKellar

Posted by: oikosasa | October 15, 2013

Like a missile attack on the ecosystem

The resilience of eco systems is studied in the new Early View paper “A new approach for rapid detection of nearby thresholds in ecosystem time series” by Stephen R. Carpenter and co-workers, in Oikos. Below is Stephen’s summary of the study:

When is the disappearance of a fish population like a missile attack? During the Cold War, scientists developed sensitive methods for detecting the radar signature of incoming missiles. More recently, ecologists have discovered that ecosystems display statistical signatures of changing resilience. The evidence of changing resilience is found in detailed observations that can be automated, like the signals from a radar installation.

Changing climate, land use, or chemical pollution can be as harmful to ecosystems as a missile impact. Gradual changes in climate  or other factors can erode resilience and lead to catastrophic changes. Conversion of a rangeland to a desert, collapse of a fishery, or explosion of toxic algae in a lake are accompanied by loss of resilience as an ecosystem is driven past a critical threshold.

When a complex system approaches a critical threshold, its behavior becomes more variable. Close to the threshold, resilience is low and variability is high. Therefore it might be possible to infer changes in resilience from changes in variability.

Research on lakes has shown that water chemistry, concentrations of algae, and even movements of animals become more variable as resilience declines. Some of these changes can be measured by new technology, such as the instruments mounted on the buoy shown in the photo

Buoy_PeterLake_2012-07-12

Our research team adapted the missile-detection methods to data from a lake that was manipulated to drive it slowly over a threshold. We gradually added largemouth bass to the lake to erode the resilience of minnows and other small fish that are prey to the bass. We found that variability increased in spatial pattern of minnows, abundance of small grazing animals in the water, concentration of algae, concentration of oxygen, and acidity of the water. In the Oikos paper, we applied the method to time series of chlorophyll, which is related only indirectly to the change in the fish. The growing variability of chlorophyll was the equivalent of a missile image on a radar screen.

About a year after the rising variability was detected, the old food chain of the lake collapsed and was replaced by a new food chain. The new food chain had no minnows, abundant grazers and very low concentrations of algae.

Although largemouth bass and missiles are quite different, both of them can completely transform their targets. The research shows how insights from one area of science can be applied in a new way. Perhaps missile-detection methods will one day monitor the resilience of lakes and other ecosystems in a changing world.

Posted by: oikosasa | October 11, 2013

Where am I and Why?

In the Early view Oikos paper “Where am I and Why? Synthesizing range biology and the eco-evolutionary dynamics of dispersal”, Alexander Kubisch, Robert D. Holt, Hans Joachim Poethke and Emanuel A. Fronhofer investigate the emergence of species’ geographic ranges and the many different forces acting on it. Here is their summary:

The distribution of species in space and time is one of the oldest puzzles in ecology. Already Charles Darwin pointed this out over 150 years ago, when he asked: “Who can explain why one species ranges widely and is very numerous, and why another allied species has a narrow range and is rare?” (Darwin 1859). And still, although much research has been invested into that topic since the times of Darwin, we still do not comprehensively understand the formation of any given species’ range.

In this paper we provide an overview of the manifold eco-evolutionary forces, which – in a metapopulation context – determine the formation of species’ ranges. Based on the idea that colonizations and local extinctions are the crucial determinants of an emerging range limit, we highlight the importance of dispersal evolution in this context. It is well known that dispersal of species is highly plastic and subject to strong evolutionary changes. However, this fact is still often ignored when distributions of species are investigated. To clarify the influences of dispersal on range formation, we organize relevant forces acting on all hierarchical levels, ranging from the landscape via genes, individuals and populations to communities, in a framework. In combination with novel simulation results this synthesis brings together the multiple interactions between these factors and forces, which may lead to high levels of complexity and non-linearity.

This contribution will build the core of an upcoming virtual special issue of Oikos, in which a compilation of studies on several aspects affecting range formation and spatial ecology will highlight and summarize the described complexities and non-linearities, which challenge our understanding of species’ distributions. Synthesizing the factors and forces affecting range formation and highlighting the importance of dispersal evolution will surely prove to be helpful in advancing our knowledge and mechanistic understanding of species’ geographic ranges.

Kubisch

Posted by: oikosasa | October 8, 2013

Multi-scale co-ocurrence patterns in India

How species associate with each other and other co-ocurrence patterns have been studied by Mahi Puri and colleagues along the west coast of India. Read the new Early View paper here:  “Multi-scale patterns in co-occurrence of rocky inter-tidal gastropods along the west coast of India

Below is a short summary by Mahi Puri:

The study was carried out as a Master’s thesis, which meant it had to be completed within a period of 6 months. The fieldwork component was only half of that duration! Having previously never worked on marine and inter-tidal fauna, I was eager to learn about this ecosystem. Most of the classical literature on intertidal fauna is based on experimental work to determine relationships between different taxa and species, done at patch level or small spatial scales. Unfortunately there has been little such work on marine ecosystems in India, though it has a really long coastline (8100 km); most of the work is either descriptive in nature or based on physiological condition affecting the distribution of species. I was interested in looking at association patterns among different species at the community level at much broader scales (essentially examine pairs of species that competed or co-occurred with one another), incorporating the expanse of the Indian west coast.

Because of the large scale of the study and the fact that we were dealing with the entire community and not just a few select species, it was not logistically feasible to incorporate experiments in this study. Based on Jared Diamond’s work on assembly rules and Nicholas Gotelli’s analytical approach (i.e. null model analysis) which did not require experiments to assess association patterns among different species, our study was designed to cover 12 sites spread across nearly 1100 km of the Indian west coast. All the study sites were rocky beaches and we looked at gastropod species occupying these rocky intertidal habitats.

We found non-random patterns of species association at large spatial scales indicating that community assembly is not determined by random factors such as tidal drift. Most pairs of species competed with one another, although the pairs with significant associations co-occurred. We also found pairs of some species displaying different association patterns in different locations i.e. they competed in some locations but co-occurred in others. This study highlights the importance of examining general patterns and of using observational studies to gain insights at multiple scales.

What effect does the moon actually have on us? And on animal populations? Find out more in the new Early View paper “Linking ‘10-year’ herbivore cycles to the lunisolar oscillation: the cosmic ray hypothesis” by Vidar Selås. Below, is Vidar’s summary of the study:

SelasMoon

The famous “10-year” population cycles of the snowshoe hare and its specialist predator, the Canada lynx, are commonly interpreted as a combined effect of predation and overgrazing. However, these mechanisms cannot explain the consistent cycle period. Herbert Archibald showed that the mean cycle period is 9.3 years, corresponding to the half period of a full 360° rotation of the Moon’s orbital plane. The same period is apparent in a 120-yr time series for the autumnal moth in Fennoscandia and an 1145-yr time series for the larch budmoth in the Alps.

SelasHare

According to Thomas C. R. White, stress factors that require increased mobilization of proteins in plants may increase protein availability above the critical threshold for herbivores. As pointed out by Charles H. Smith, hare cycles are most pronounced in areas with low protection against cosmic rays. Because repair of damages caused by cosmic rays require protein mobilization in plants, and cosmic ray fluxes are affected by the position of the Moon, cosmic rays may be the link between the lunar and herbivore cycles.

Cosmic rays are high-speed charged particles (mainly protons), which are deflected by a sufficiently strong magnetic field and absorbed by a sufficiently thick air layer. The protection provided by the Sun’s magnetic field, which reaches far beyond the Earth’s orbit, fluctuates with the 11-yr solar cycle. The protection provided by the Earth’s magnetic field decreases from equator to the magnetic poles, whereas the protection provided by the Earth’s atmosphere decreases with elevation.

In the atmosphere, secondary cosmic rays are created by collisions between primary cosmic rays and air molecules. Because the most important secondary cosmic rays, muons, are short-lived, only protons with sufficiently high speed are able to produce muons that reach the ground. When eclipses occur close to solstice, which happens at 9.3-yr intervals, the Moon enhances the Sun-Earth magnetic connection, so that more solar energetic particles hit the Earth’s magnetic field. This results in increased temperatures and an expansion of the atmosphere, making it more difficult for muons to reach the ground. The effect of the Moon is probably most important in areas where the protection against cosmic rays is low. In areas with better protection, the 11-yr solar signal would be expected to prevail.

VidarSelas3

Posted by: oikosasa | October 1, 2013

Temperature variability and population dynamics

A new theoretical model to better study of the role temperature variability plays on individual performance and population dynamics, is presented in the new Early View paper “The role of temperature variability on insect performance and population dynamics in a warming world” by Sergio A. Estay et al.

Watch Sergio’s summary of the study on Youtube:

http://www.youtube.com/watch?v=9_Pbmb8n4zk&feature=youtu.be

Posted by: oikosasa | September 24, 2013

Ecological periodic tables

Can ecological patterns be organized in a “Periodic table”? Find out in the Early View paper  “Ecological periodic tables: in principle and practice” by  Steven P. Ferraro.

Watch Steven’s talk about it here:

http://my.brainshark.com/Periodic-Tables-PeerOvation-486260509

and look at the slides from a talk about it here:

http://f1000.com/posters/browse/summary/1092512

OIK_717_f1

Posted by: oikosasa | September 20, 2013

Mind your “girth”!

What body condition index is best? Studied for mice in the new Early View paper by Marta K Labocha and co-workers. Below is a summary by Marta:

In humans, BMI (or the body mass index) is a widely used indicator of a person’s body fat.  In animals other than humans, body fat is also important because animals with more fat typically have greater energy reserves which may allow them to better cope with stressful conditions.   In animals, these indicators of body fat (and sometime other indicators of animal quality) are called condition indices.  These condition indices are typically determined from body measurements, but exactly which measurements to use is both unclear and a topic of keen interest.  Many conditions indices are used without being tested for their accuracy.  To test these indices, we compared how well a broad range of body condition indices predicted body fat content in mice Mus musculus. We also compared the performance of these condition indices with a statistical technique, multiple regression of several morphometric variables (body measurements) on body fat content. Multiple regressions incorporating pelvic circumference (i.e., girth at the iliac crests –around the widest part of the hips) were the best predictors of body fat content and were better than any of the condition indices. So, perhaps not surprisingly, mice with bigger waists are fatter.  What is surprising is that this method has not been used before for mice.  Our results suggest a way to improve condition mass indices for mice, and our methods may be useful for other animals as well.

Posted by: oikosasa | September 13, 2013

Dispersal at the heart of our thinking

Read Justin Travis’ and co-workers’ Forum paper “Dispersal and species’ responses to climate change” in Oikos Early View. Below is Justin’s background story to the paper:

Over the last decade or so there have been a series of meetings and workshops involving individuals interested in a broad range of issues related to causes and consequences of dispersal. These have involved people focused on a range of animal and plant systems, adopting field and lab based approaches and also including people developing models for theory and also for prediction. One of the group’s recent meetings took place immediately after the European Ecological Federation Congress in Avila held in 2011. Maria Delgado had organised a casa for us in a tiny village called Tabladillos, close to Segovia. Our objective was to collectively evaluate how dispersal is likely to be impacted by climate change and also how dispersal, and changes in dispersal, are likely to impact species’ responses to climate change.  After an excellent few days, full of interesting discussion, plenty of relaxing in the sun, BBQs and fine Spanish wine (see photo 2) we left with a first rough draft of a manuscript and a long list of allocated tasks.

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!

Kamil’s photographic trickery captures the group enjoying an evening meal!

Kamil’s photographic trickery captures the group enjoying an evening meal!

The final result of this team effort (see photo 3) is now published by Oikos http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0706.2013.00399.x/abstract and we hope it serves to emphasise just how important it is to increase our understanding of the eco-evolutionary dynamics of dispersal under climate change for understanding how species will fare over the coming decades.

The workshop participants with our canine mascot, Karhu!

The workshop participants with our canine mascot, Karhu!

We argue that it is particularly important that conservation actions are founded on a better understanding of dispersal. There is already a large body of knowledge on this key process that can inform current management plans but important knowledge gaps remain where future research is required. Finally, not wanting to miss an obvious chance for advertisement, the next meeting organised by the informal dispersal working group will be in Aberdeen in November. It will take the form of a conference and the objective of this meeting is to seek greater integration both between the fields of dispersal ecology and movement ecology and also between researchers working in terrestrial and marine systems (see http://www.abdn.ac.uk/events/mad-2013/ for details).

 

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