Consequences For Community Dynamics Research Articles

Beneath the Leaf-Litter: Can Salamander Personality Influence Forest-Floor Dynamics?

Ecological research demonstrates how intraspecific phenotypic variation can have consequences for community dynamics. However, the effects of animal personalities (i.e., intraspecific behavioral variation) on ecological processes remains relatively understudied. Using Red-backed Salamanders (Plethodon cinereus) and the detrital food web as a model system, we conducted a laboratory mesocosm experiment to explore whether or not the personality type of a top-level predator could affect the community structure within a complex, terrestrial food web. We used behavioral assays to investigate the repeatability of salamander behaviors, and classified individuals as either active or inactive. We then subjected laboratory mesocosms to one of four treatments for 3 mo: one active salamander, one inactive salamander, control (no salamander), and a pre-experimental reference. Our results indicate that the effect of P. cinereus on the detrital food web might be behaviorally mediated, with only the most active salamanders affecting community structure. Specifically, mesocosms housing active salamanders contained less diverse invertebrate communities than all other treatments. This difference was primarily driven by springtails, which were more abundant within mesocosms housing active salamanders. We also found that salamander personality was associated with cover board use inside mesocosms, with inactive salamanders exhibiting a more philopatric use of cover objects than active individuals. Leaf-litter degradation did not differ between treatments, indicating that the ecological effects of salamanders were too weak to influence basal resources within the detrital food web. Our study prompts further questions regarding the potential for animal personalities to influence ecological processes within terrestrial communities.

Shifting daylength regimes associated with range shifts alter aphid-parasitoid community dynamics.

With climate change leading to poleward range expansion of species, populations are exposed to new daylength regimes along latitudinal gradients. Daylength is a major factor affecting insect life cycles and activity patterns, so a range shift leading to new daylength regimes is likely to affect population dynamics and species interactions; however, the impact of daylength in isolation on ecological communities has not been studied so far. Here, we tested for the direct and indirect effects of two different daylengths on the dynamics of experimental multitrophic insect communities. We compared the community dynamics under “southern” summer conditions of 14.5‐hr daylight to “northern” summer conditions of 22‐hr daylight. We show that food web dynamics indeed respond to daylength with one aphid species (Acyrthosiphon pisum) reaching much lower population sizes at the northern daylength regime compared to under southern conditions. In contrast, in the same communities, another aphid species (Megoura viciae) reached higher population densities under northern conditions. This effect at the aphid level was driven by an indirect effect of daylength causing a change in competitive interaction strengths, with the different aphid species being more competitive at different daylength regimes. Additionally, increasing daylength also increased growth rates in M. viciae making it more competitive under summer long days. As such, the shift in daylength affected aphid population sizes by both direct and indirect effects, propagating through species interactions. However, contrary to expectations, parasitoids were not affected by daylength. Our results demonstrate that range expansion of whole communities due to climate change can indeed change interaction strengths between species within ecological communities with consequences for community dynamics. This study provides the first evidence of daylength affecting community dynamics, which could not be predicted from studying single species separately.

Neighbourhood effects on plant reproduction: An experimental–analytical framework and its application to the invasive Senecio inaequidens

Abstract Density dependence is of fundamental importance for population and range dynamics. Density‐dependent reproduction of plants arises from competitive and facilitative plant–plant interactions that can be pollination independent or pollination mediated. In small and sparse populations, conspecific density dependence often turns from negative to positive and causes Allee effects. Reproduction may also increase with heterospecific density (community‐level Allee effect), but the underlying mechanisms are poorly understood and the consequences for community dynamics can be complex. Allee effects have crucial consequences for the conservation of declining species, but also the dynamics of range edge populations. In invasive species, Allee effects may slow or stop range expansion. Observational studies in natural plant communities cannot distinguish whether reproduction is limited by pollination‐mediated interactions among plants or by other neighbourhood effects (e.g. competition for abiotic resources). Even experimental pollen supply cannot distinguish whether variation in reproduction is caused by direct density effects or by plant traits correlated with density. Finally, it is unknown over which spatial scales pollination‐mediated interactions occur. To circumvent these problems, we introduce a comprehensive experimental and analytical framework which simultaneously (1) manipulates pollen availability and quality by hand pollination and pollinator exclusion, (2) manipulates neighbourhoods by transplanting target plants, and (3) analyses the effects of con‐ and heterospecific neighbourhoods on reproduction with spatially explicit trait‐based neighbourhood models. Applying this framework to Senecio inaequidens, one of Europe's fastest plant invaders, we found that the seed set was strongly pollen limited. Reproduction had increased by pollinator‐mediated facilitation by both con‐ and heterospecific neighbours which may lead to (community‐level) Allee effects. Pollination‐independent interactions, such as amelioration of abiotic conditions through neighbours, contributed to additional positive neighbour effects. However, these pollination‐independent interactions were weaker than the pollination‐mediated interactions and they occurred over smaller spatial scales. Finally, the strength and direction of neighbourhood effects depended on neighbour traits and thus changed with the trait composition of the neighbourhood. Synthesis. By manipulating both pollen availability and target plant locations within neighbourhoods, we can comprehensively analyse spatially explicit density dependence of plant reproduction. This experimental approach enhances our ability to understand the dynamics of sparse populations and of species geographical ranges.

How Structured Is the Entangled Bank? The Surprisingly Simple Organization of Multiplex Ecological Networks Leads to Increased Persistence and Resilience.

Species are linked to each other by a myriad of positive and negative interactions. This complex spectrum of interactions constitutes a network of links that mediates ecological communities’ response to perturbations, such as exploitation and climate change. In the last decades, there have been great advances in the study of intricate ecological networks. We have, nonetheless, lacked both the data and the tools to more rigorously understand the patterning of multiple interaction types between species (i.e., “multiplex networks”), as well as their consequences for community dynamics. Using network statistical modeling applied to a comprehensive ecological network, which includes trophic and diverse non-trophic links, we provide a first glimpse at what the full “entangled bank” of species looks like. The community exhibits clear multidimensional structure, which is taxonomically coherent and broadly predictable from species traits. Moreover, dynamic simulations suggest that this non-random patterning of how diverse non-trophic interactions map onto the food web could allow for higher species persistence and higher total biomass than expected by chance and tends to promote a higher robustness to extinctions.

Evolutionary response of plant interaction traits to nutrient enrichment modifies the assembly and structure of antagonistic‐mutualistic communities

Summary Nutrient enrichment is one of the major threats acting on natural communities. The ecological consequences of this disturbance for ecosystems have been largely studied, but we still have little knowledge on its evolutionary effects at community scale. We are interested in the evolutionary consequences of nutrient enrichment for plant interaction traits, embedded in complex communities made of antagonistic and mutualistic interactions. We built a mathematical model of a plant–pollinator–herbivore community confronted by nutrient enrichment. Plants have an interaction trait that is involved in an ecological trade‐off. An increase in this trait, leading to more attractive phenotypes, increases the strength of both interactions with pollinators and herbivores. A lower value of this trait leads to defensive phenotypes with weak interactions with both herbivores and pollinators. We use the framework of adaptive dynamics to study the evolutionary dynamics of this kind of traits and the consequences for community dynamics. We found that evolutionary dynamics of plants modify the assembly of the community along a nutrient enrichment gradient. Due to top‐down controls, herbivory leads to priority effects when only ecological dynamics are considered. Evolution of the plant interaction trait alleviates this priority effect and facilitates community assembly. In the three‐species community, we find that nutrient enrichment leads to more defended phenotypes of plants, at the expense of pollinator attraction. We find that, when the ecological trade‐off between pollination and herbivory is convex, evolution of interaction trait may lead to plant diversification. Two plant phenotypes then coexist in the community, one which is highly attractive and one which is highly defensive. Synthesis. Our results suggest that accounting for evolutionary dynamics will profoundly modify the dynamics of communities in the face of nutrient enrichment. Both community assembly and equilibrium dynamics are altered and enrichment may even lead to diversification. These results advocate for the development of an eco‐evolutionary theory of nutrient enrichment and may be particularly important in agro‐ecosystems relying on fertilization.

Trait contributions to fish community assembly emerge from trophic interactions in an individual-based model

Community ecology seeks to understand and predict the characteristics of communities that can develop under different environmental conditions, but most theory has been built on analytical models that are limited in the diversity of species traits that can be considered simultaneously. We address that limitation with an individual-based model to simulate assembly of fish communities characterized by life history and trophic interactions with multiple physiological tradeoffs as constraints on species performance. Simulation experiments were carried out to evaluate the distribution of 6 life history and 4 feeding traits along gradients of resource productivity and prey accessibility. These experiments revealed that traits differ greatly in importance for species sorting along the gradients. Body growth rate emerged as a key factor distinguishing community types and defining patterns of community stability and coexistence, followed by egg size and maximum body size. Dominance by fast-growing, relatively large, and fecund species occurred more frequently in cases where functional responses were saturated (i.e. high productivity and/or prey accessibility). Such dominance was associated with large biomass fluctuations and priority effects, which prevented richness from increasing with productivity and may have limited selection on secondary traits, such as spawning strategies and relative size at maturation. Our results illustrate that the distribution of species traits and the consequences for community dynamics are intimately linked and strictly dependent on how the benefits and costs of these traits are balanced across different conditions.

Genetic diversity of a dominant C4 grass is altered with increased precipitation variability

Climate change has the potential to alter the genetic diversity of plant populations with consequences for community dynamics and ecosystem processes. Recent research focused on changes in climatic means has found evidence of decreased precipitation amounts reducing genetic diversity. However, increased variability in climatic regimes is also predicted with climate change, but the effects of this aspect of climate change on genetic diversity have yet to be investigated. After 10 years of experimentally increased intra-annual variability in growing season precipitation regimes, we report that the number of genotypes of the dominant C(4) grass, Andropogon gerardii Vitman, has been significantly reduced in native tallgrass prairie compared with unmanipulated prairie. However, individuals showed a different pattern of genomic similarity with increased precipitation variability resulting in greater genome dissimilarity among individuals when compared to unmanipulated prairie. Further, we found that genomic dissimilarity was positively correlated with aboveground productivity in this system. The increased genomic dissimilarity among individuals in the altered treatment alongside evidence for a positive correlation of genomic dissimilarity with phenotypic variation suggests ecological sorting of genotypes may be occurring via niche differentiation. Overall, we found effects of more variable precipitation regimes on population-level genetic diversity were complex, emphasizing the need to look beyond genotype numbers for understanding the impacts of climate change on genetic diversity. Recognition that future climate change may alter aspects of genetic diversity in different ways suggests possible mechanisms by which plant populations may be able to retain a diversity of traits in the face of declining biodiversity.

Role of biological habitat amelioration in altering the relative responses of congeneric species to climate change

The distribution of most species is expected to alter in response to climate change. Pre- dictions for the extent of these range shifts are frequently based on 'climate envelope' approaches, which often oversimplify species responses because many do not consider interactions between physical and biological factors. The local persistence of some species, however, is likely to be strongly modulated by microhabitat-forming organisms. Using congeneric patellid gastropods with northern/ boreal and southern/lusitanian distributions, we have demonstrated how the loss of habitat-forming macroalgal species could modify species responses to climate change. The northern limpet Patella vulgata preferentially aggregates beneath Fucus spp. When Fucus vesiculosus was experimentally removed, to simulate a decline in macroalgal abundance in response to climatic warming, P. vulgata suffered increased mortality or relocated home scars, often to nearby Fucus spp. patches. In contrast, the southern limpet P. depressa did not aggregate beneath Fucus spp. and showed no response in terms of movement or mortality to the loss of F. vesiculosus. Based on these results, we predict that the loss of Fucus spp. will influence the relative abundance of these 2 limpet species, particularly at the distributional limit of Fucus spp. In addition, differences in the aggregative behaviour of these limpet species will result in changes in the spatial distribution of grazing in the intertidal, with likely consequences for community dynamics. These outcomes could not be anticipated from predictions based on direct responses to temperature alone, highlighting the need for biotic and abiotic factors to be incorporated into predictions of species responses to climate change.