Posted by: oikosasa | April 29, 2014

Dispersal and endoparasites in roe deer

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

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

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

 

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

 

Collection of faeces sample during marking

Collection of faeces sample during marking

 


Roedeer3aRoedeer3b

Roedeer3c

Back to the field with a beautiful GPS collar

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

The authors through Lucie Debeffe who also took the photos

Posted by: oikosasa | April 23, 2014

Geographic variation in bird survival

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

Jared Wolfe with Wing-banded Antbird in the central Amazon

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

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

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

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

Posted by: oikosasa | April 22, 2014

Herbivory, competition and global warming

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

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

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

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

 

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

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

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

Posted by: oikosasa | April 15, 2014

Climate effects on plant chemistry

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

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

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

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

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

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

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

Pratt_sagebrush

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

California Sagebrush experimental garden plot

California Sagebrush experimental garden plot

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

Pratt_sagebrush

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

Posted by: oikosasa | April 11, 2014

Haiku on risky dispersal

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

risky dispersal
whether too much, too little
both suboptimal

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

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

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

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

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

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

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

 

 

Dispersal

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

 

 

 

 

Posted by: oikosasa | April 8, 2014

Apex predators on coral reefs

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

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Figure 1. Location of study site

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

 

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

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

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

Justin1

 

Posted by: oikosasa | April 4, 2014

Severe geographic bias in pollination studies

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

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

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

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

Posted by: oikosasa | April 1, 2014

Metapopulation modeling of endangered rabbits

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

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

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

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

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

 

Posted by: oikosasa | March 28, 2014

Meta-community structure in rodent parasites

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

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

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

 

 

Dallas 

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

 

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

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

 

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

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

Posted by: oikosasa | March 27, 2014

Effects of small mammal outbreaks in the Serengeti

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

Tropical savanna woodland, Serengeti National Park

Tropical savanna woodland, Serengeti National Park

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

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Arvicanthus niloticus, the African grass rat

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

Black-chested snake eagle, Circaetus pectoralis

Black-chested snake eagle, Circaetus pectoralis

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

 

The serval, Leptailurus serval

The serval, Leptailurus serval

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

Byrom2

 

Posted by: oikosasa | March 25, 2014

Life hots up for long-tailed tits

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

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

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

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

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

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

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

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

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

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

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

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

conditions reduce the costs of breeding.

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

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

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

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

Posted by: oikosasa | March 18, 2014

Effect of coffee farming on soil biota

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

Pizano2

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

Pizano3Pizano3

Posted by: oikosasa | March 17, 2014

Bigger fishes are more predictable

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

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

sockeye_armstrong

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

cohoSockeye_armstrong

Posted by: oikosasa | March 14, 2014

Top-predator effects on variable environments

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

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

Abedus_vs_Oplonaeshna2

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

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

Posted by: oikosasa | March 13, 2014

Which fruit should I choose?

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

Rodrigues1

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

Rodrigues 2Rodrigues3

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

Rodrigues4

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

Rodrigues5

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

Artwork and photo credits: Daniel Martínez.

Posted by: oikosasa | March 12, 2014

Ecosystem engineering in food-webs

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

Myror

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

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

Posted by: oikosasa | March 11, 2014

Modelling of human-driven changes in meta-communities

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

Below is the author’s summary of the paper:

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

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

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

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

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

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

Posted by: oikosasa | March 7, 2014

Factors affecting carbon cycling in Sphagnum

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

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

Laing1

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

Laing2

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

Posted by: oikosasa | March 5, 2014

Ecological networks and inference

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

dreamstime_m_14830510

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

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

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

Posted by: oikosasa | March 4, 2014

Invasive flowers, pollinators and native flowers

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

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

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

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

hypfig

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

Posted by: oikosasa | March 3, 2014

Welcome Martijn Bezemer, new SE

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

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

Can you describe you research career?

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

Bezemer field

How come that you became a scientist in ecology?

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

What do you do when you’re not working?

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

Posted by: oikosasa | February 28, 2014

Editor’s Choice Feb-March 2014

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

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

 

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

 

Posted by: oikosasa | February 27, 2014

Cows and rabbits change plant growth via the soil

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

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

Coxsandrabbits1

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

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

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

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

Posted by: oikosasa | February 25, 2014

Most downloaded 2013 papers

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

Here’s a link to the top 10 list:

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

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

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

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

Dispersal and species’ responses to climate change with 1384 downloads

by J. Travis et al.

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

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

and

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

by Zenni and Nunez

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

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

Posted by: oikosasa | February 21, 2014

Bottom-up effects of hybridization

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

Below is their popular summary of the study:

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

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

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

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

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

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

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

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

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

 SantaCalus

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

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

Tina Heger & Jonathan M. Jeschke

Posted by: oikosasa | February 14, 2014

Bob Holt – prize winner 2014

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

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

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

Bobs talk

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

Bob prize

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

Take a closer look at Bob’s diploma:

Diploma

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

Posted by: oikosasa | January 31, 2014

Salmon response to climate variations

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

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

Griffiths_FieldCamp2_OIK-00801R2

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

Griffiths_MeasuredSockeye_OIK-00801R2

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

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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.

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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.

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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!

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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.

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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.

dragonfly_larva_eating_tadpole

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

Dries

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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               815b

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

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