Temporal dynamics of a local fish community are strongly affected by immigration from the surrounding metacommunity

A 5‐year time series of annual censuses was collected from a large floodplain lake to determine how dynamics of the local fish community were affected by changes in hydrological connectivity with the surrounding metacommunity. The lake was disconnected from the metacommunity for 1 year prior to our study and remained disconnected until 3 months before our third annual census, when a flood reconnected the lake to the metacommunity. We determined how changes in connectivity affected temporal dynamics of (1) local community composition and (2) the population composition, condition, and growth of catfish, to shed light on how immigration of other species might affect local population dynamics. Before reconnection, the community was likely shaped by interactions between the local environment and species traits. The reconnection caused significant immigration and change in community composition and correlated with a significant and abrupt decline in catfish condition, growth, and abundance; effects likely due to the immigration of a competitor with a similar trophic niche: carp. The community was slow to return to its preconnection state, which may be due to dispersal traits of the fishes, and a time‐lag in the recovery of the local catfish population following transient intensification of species interactions. The dynamics observed were concordant with the species sorting and mass‐effects perspectives of metacommunity theory. Floods cause episodic dispersal in floodplain fish metacommunities, and so, flood frequency determines the relative importance of regional and local processes. Local processes may be particularly important to certain species, but these species may need sufficient time between floods for population increase, before the next flood‐induced dispersal episode brings competitors and predators that might cause population decline. Accordingly, species coexistence in these metacommunities may be facilitated by spatiotemporal storage effects, which may in turn be regulated by flood frequency.     

Using functional diversity patterns to explore metacommunity dynamics: a framework for understanding local and regional influences on community structure

The metacommunity concept, describing how local and regional scale processes interact to structure communities, has been successfully applied to patterns of taxonomic diversity. Functional diversity has proved useful for understanding local scale processes, but has less often been applied to understanding regional scale processes. Here, we explore functional diversity patterns within a metacommunity context to help elucidate how local and regional scale processes influence community assembly. We detail how each of the four metacommunity perspectives (species sorting, mass effects, patch dynamics, neutral) predict different patterns of functional beta‐ and alpha‐diversity and spatial structure along two key gradients: dispersal limitation and environmental conditions. We then apply this conceptual model to a case study from alpine tundra plant communities. We sampled species composition in 17 ‘sky islands’ of alpine tundra in the Colorado Rocky Mountains, USA that differed in geographic isolation and area (key factors related to dispersal limitation) and temperature and elevation (key environmental factors). We quantified functional diversity in each site based on specific leaf area, leaf area, stomatal conductance, plant height and chlorophyll content. We found that colder high elevation sites were functionally more similar to each other (decreased functional beta‐diversity) and had lower functional alpha‐diversity. Geographic isolation and area did not influence functional beta‐ or alpha‐diversity. These results suggest a strong role for environmental conditions structuring alpine plant communities, patterns consistent with the species sorting metacommunity perspective. Incorporating functional diversity into metacommunity theory can help elucidate how local and regional factors structure communities and provide a framework for observationally examining the role of metacommunity dynamics in systems where experimental approaches are less tractable.     

A simulation‐based approach to understand how metacommunity characteristics influence emergent biodiversity patterns

To understand controls over biodiversity, it is necessary to take a multi‐scale approach to understand how local and regional factors affect the community assembly processes that drive emergent patterns. This need is reflected in the growing use of the metacommunity concept to interpret multi‐scale measures of biodiversity, including metrics derived from diversity partitioning (e.g. α, β and γ diversity) and variation partitioning (e.g. spatial and environmental components of compositional turnover) techniques. However, studies have shown limited success using these metrics to characterize underlying community assembly dynamics. Here we demonstrate how a metacommunity simulation package (MCSim) can be used to evaluate when and how biodiversity metrics can be used to make inferences about metacommunity characteristics. We examined a wide range of parameter settings representing ecologically relevant scenarios. We used artificial neural networks (ANNs) to assess the sensitivity of diversity and variation partitioning metrics (calculated from simulation outcomes) to metacommunity parameter settings. In the scenarios examined in this study, the niche‐neutral gradient strongly influenced most biodiversity metrics, metacommunity size exhibited a marginal influence over some metrics, and dispersal dynamics only affected a subset of variation partitioning outcomes. Variation partitioning response curves along the niche‐neutral gradient were not monotonic; however, simulation outcomes suggest other biodiversity metrics (e.g. dissimilarity saturation) can be used in combination with variation partitioning metrics to make inferences about metacommunity properties. With the growing availability of archived ecological data, we expect future work will apply simulation‐based techniques to better understand links between biodiversity and the metacommunity characteristics that are presumed to control the underlying community assembly processes.     

The community ecology of pathogens: coinfection,coexistence and community composition

Disease and community ecology share conceptual and theoretical lineages, and there has been a resurgence of interest in strengthening links between these fields. Building on recent syntheses focused on the effects of host community composition on single pathogen systems, we examine pathogen (microparasite) communities using a stochastic metacommunity model as a starting point to bridge community and disease ecology perspectives. Such models incorporate the effects of core community processes, such as ecological drift, selection and dispersal, but have not been extended to incorporate host–pathogen interactions, such as immunosuppression or synergistic mortality, that are central to disease ecology. We use a two‐pathogen susceptible‐infected (SI) model to fill these gaps in the metacommunity approach; however, SI models can be intractable for examining species‐diverse, spatially structured systems. By placing disease into a framework developed for community ecology, our synthesis highlights areas ripe for progress, including a theoretical framework that incorporates host dynamics, spatial structuring and evolutionary processes, as well as the data needed to test the predictions of such a model. Our synthesis points the way for this framework and demonstrates that a deeper understanding of pathogen community dynamics will emerge from approaches working at the interface of disease and community ecology.     

Condition‐dependent movement and dispersal in experimental metacommunities

Dispersal and the underlying movement behaviour are processes of pivotal importance for understanding and predicting metapopulation and metacommunity dynamics. Generally, dispersal decisions are condition‐dependent and rely on information in the broad sense, like the presence of conspecifics. However, studies on metacommunities that include interspecific interactions generally disregard condition‐dependence. Therefore, it remains unclear whether and how dispersal in metacommunities is condition‐dependent and whether rules derived from single‐species contexts can be scaled up to (meta)communities. Using experimental protist metacommunities, we show how dispersal and movement depend on and are adjusted by the strength of interspecific interactions. We found that the predicting movement and dispersal in metacommunities requires knowledge on behavioural responses to intra‐ and interspecific interaction strengths. Consequently, metacommunity dynamics inferred directly from single‐species metapopulations without taking interspecific interactions into account are likely flawed. Our work identifies the significance of condition‐dependence for understanding metacommunity dynamics, stability and the coexistence and distribution of species.     

Local community size mediates ecological drift and competition in metacommunities

The outcome of competitive interactions is likely to be influenced by both competitive dominance (i.e. niche-based dynamics) and ecological drift (i.e. neutral dynamics governed by demographic stochasticity). However, spatial models of competition rarely consider the joint operation of these two processes. We develop a model based on the original competition-colonization trade-off model that incorporates niche and neutral processes and several realistic facets of ecological dynamics: it allows local competition (i.e. competition within a patch) to occur within communities of a finite size, it allows competitors to vary in the degree of competitive asymmetry, and it includes the role of local migration (i.e. propagule pressure). The model highlights the role of community size, i.e. the number of competitors in the local community, in mediating the relative importance of stochastic and deterministic forces. In metacommunities where local communities are small, ecological drift is substantial enough that strong competitors become effectively neutral, creating abrupt changes in the outcome of competition not predicted by the standard competition-colonization trade-off. Importantly, the model illustrates that, even when other aspects of species interactions (e.g. migration ability, competitive ability) are unchanged, local community size can alter the dynamics of metacommunity persistence. Our work demonstrates that activities which reduce the size of local communities, such as habitat destruction and degradation, effectively compound the extinction debt.     

Effective dispersal rate is a function of habitat size and corridor shape: mechanistic formulation of a two‐patch compartment model for spatially continuous systems

Two‐patch compartment models have been explored to understand the spatial processes that promote species coexistence. However, a phenomenological definition of the inter‐patch ‘dispersal rate’ has limited the quantitative predictability of these models to community dynamics in spatially continuous habitats. Here, we mechanistically rederived a two‐patch Lotka–Volterra competition model for a spatially continuous reaction‐diffusion system where a narrow corridor connects two large habitats. We provide a mathematical formula of the dispersal rate appearing in the two‐patch compartment model as a function of habitat size, corridor shape (ratio of its width to its length), and organism diffusion coefficients. For most reasonable settings, the two‐patch compartment model successfully approximated not only the steady states, but also the transient dynamics of the reaction–diffusion model. Further numerical simulations indicated the general applicability of our formula to other types of community dynamics, e.g. driven by resource‐competition, in spatially homogeneous and heterogeneous environments. Our results suggest that the spatial configuration of habitats plays a central role in community dynamics in space. Furthermore, our new framework will help to improve experimental designs for quantitative test of metacommunity theories and reduce the gaps among modeling, empirical studies, and their application to landscape management.     

Towards understanding the organisation of metacommunities in highly dynamic ecological systems

Community ecology recognises today that local biological communities are not only affected by local biotic interactions and abiotic environmental conditions, but also by regional processes (e.g. dispersal). While much is known about how metacommunities are organised in space in terrestrial, marine and freshwater ecological systems, their temporal variations remain poorly studied. Here, we address the question of the dynamics of metacommunities in highly variable systems, using intermittent rivers (IRs), those rivers which temporarily stop flowing or dry up, as a model system. We first review how habitat heterogeneity in space and time influences metacommunity organisation. Second, we compare the metacommunities in IRs to those in perennial rivers (PRs) and develop the idea that IRs could undergo highly dynamic shifts due to the temporal variability in local and regional community processes. Third, we develop the idea that in IRs, metacommunities of the wet and dry phases of IRs are closely intertwined, thereby increasing even more their respective temporal dynamics. Last, we provide a roadmap to stimulate further conceptual and empirical developments of metacommunity research and identify possible applications for improving the management of IRs and other highly dynamic ecological systems. Synthesis Extensive research has examined the importance of local biotic interactions, environmental filtering, and regional processes on community assembly. Movement of organisms between sites, i.e. dispersal, is a major set of processes within this framework. However, subsequent metacommunity organisation also varies over time in ecosystems because habitat characteristics such as configuration and composition continuously shift. Intermittent rivers are an ideal set of systems to examine these ideas because these freshwater systems temporarily cease flowing thereby limiting dispersal events. We proposed the hypothesis that metacommunities in dynamic ecosystems will undergo frequent shifts in structure and composition in response to the temporal variability in environmental filtering and dispersal. In addition to providing a roadmap for developing a more dynamic perspective for community ecology, these framework provides direct insights for the management of intermittent rivers.     

Linking metacommunity theory and symbiont evolutionary ecology

Processes that occur both within and between hosts can influence the ecological and evolutionary dynamics of symbionts, a broad term that includes parasitic and disease-causing organisms. Metacommunity theory can integrate these local- and regional-scale dynamics to explore symbiont community composition patterns across space. In this article I emphasize that symbionts should be incorporated into the metacommunity concept. I highlight the utility of metacommunity theory by discussing practical and general benefits that emerge from considering symbionts in a metacommunity framework. Specifically, investigating the local and regional drivers of symbiont community and metacommunity structure will lead to a more holistic understanding of symbiont ecology and evolution and could reveal novel insights into the roles of symbiont communities in mediating host health.     

An integrative framework of coexistence mechanisms in competitive metacommunities

Species distribution in a metacommunity varies according to their traits, the distribution of environmental conditions and connectivity among localities. These ingredients contribute to coexistence across spatial scales via species sorting, patch dynamics, mass effects and neutral dynamics. These mechanisms however seldom act in isolation and the impact of landscape configuration on their relative importance remains poorly understood. We present a new model of metacommunity dynamics that simultaneously considers these four possible mechanisms over spatially explicit landscapes and propose a statistical approach to partition their contribution to species distribution. We find that landscape configuration can induce dispersal limitations that have negative consequences for local species richness. This result was more pronounced with neutral dynamics and mass effect than with species sorting or patch dynamics. We also find that the relative importance of the four mechanisms varies not only among landscape configurations, but also among species, with some species being mostly constrained by dispersal and/or drift and others by sorting. Changes in landscape properties might lead to a shift in coexistence mechanisms and, by extension, to a change in community composition. This confirms the importance of considering landscape properties for conservation and management. Our results illustrate the idea that ecological communities are the results of multiple mechanisms acting at the same time and complete our understanding of spatial processes in competitive metacommunities.     

Extinction debt in source-sink metacommunities

In an increasingly modified world, understanding and predicting the consequences of landscape alteration on biodiversity is a challenge for ecologists. To this end, metacommunity theory has developed to better understand the complexity of local and regional interactions that occur across larger landscapes. While metacommunity ecology has now provided several alternative models of species coexistence at different spatial scales, predictions regarding the consequences of landscape alteration have been done exclusively for the competition-colonization trade off model (CC). In this paper we investigate the effects of landscape perturbation on source-sink metacommunities. We show that habitat destruction perturbs the equilibria among species competitive effects within the metacommunity, driving both direct extinctions and an indirect extinction debt. As in CC models, we found a time lag for extinction following habitat destruction that varied in length depending upon the relative importance of direct and indirect effects. However, in contrast to CC models, we found that the less competitive species are more affected by habitat destruction. The best competitors can sometimes even be positively affected by habitat destruction, which corresponds well with the results of field studies. Our results are complementary to those results found in CC models of metacommunity dynamics. From a conservation perspective, our results illustrate that landscape alteration jeopardizes species coexistence in patchy landscapes through complex indirect effects and delayed extinctions patterns.     

Predicting food‐web structure with metacommunity models

Synthesis Metacommunity theory aims to elucidate the relative influence of local and regional‐scale processes in generating diversity patterns across the landscape. Metacommunity research has focused largely on assemblages of competing organisms within a single trophic level. Here, we test the ability of metacommunity models to predict the network structure of the aquatic food web found in the leaves of the northern pitcher plant Sarracenia purpurea. The species‐sorting and patch‐dynamics models most accurately reproduced nine food web properties, suggesting that local‐scale interactions play an important role in structuring Sarracenia food webs. Our approach can be applied to any well‐resolved food web for which data are available from multiple locations. The metacommunity framework explores the relative influence of local and regional‐scale processes in generating diversity patterns across the landscape. Metacommunity models and empirical studies have focused mostly on assemblages of competing organisms within a single trophic level. Studies of multi‐trophic metacommunities are predominantly restricted to simplified trophic motifs and rarely consider entire food webs. We tested the ability of the patch‐dynamics, species‐sorting, mass‐effects, and neutral metacommunity models, as well as three hybrid models, to reproduce empirical patterns of food web structure and composition in the complex aquatic food web found in the northern pitcher plant Sarracenia purpurea. We used empirical data to determine regional species pools and estimate dispersal probabilities, simulated local food‐web dynamics, dispersed species from regional pools into local food webs at rates based on the assumptions of each metacommunity model, and tested their relative fits to empirical data on food‐web structure. The species‐sorting and patch‐dynamics models most accurately reproduced nine food web properties, suggesting that local‐scale interactions were important in structuring Sarracenia food webs. However, differences in dispersal abilities were also important in models that accurately reproduced empirical food web properties. Although the models were tested using pitcher‐plant food webs, the approach we have developed can be applied to any well‐resolved food web for which data are available from multiple locations.     

What can observational data reveal about metacommunity processes?

A key challenge for community ecology is to understand to what extent observational data can be used to infer the underlying community assembly processes. As different processes can lead to similar or even identical patterns, statistical analyses of non‐manipulative observational data never yield undisputable causal inference on the underlying processes. Still, most empirical studies in community ecology are based on observational data, and hence understanding under which circumstances such data can shed light on assembly processes is a central concern for community ecologists. We simulated a spatial agent‐based model that generates variation in metacommunity dynamics across multiple axes, including the four classic metacommunity paradigms as special cases. We further simulated a virtual ecologist who analysed snapshot data sampled from the simulations using eighteen output metrics derived from beta‐diversity and habitat variation indices, variation partitioning and joint species distribution modelling. Our results indicated two main axes of variation in the output metrics. The first axis of variation described whether the landscape has patchy or continuous variation, and thus was essentially independent of the properties of the species community. The second axis of variation related to the level of predictability of the metacommunity. The most predictable communities were niche‐based metacommunities inhabiting static landscapes with marked environmental heterogeneity, such as metacommunities following the species sorting paradigm or the mass effects paradigm. The most unpredictable communities were neutral‐based metacommunities inhabiting dynamics landscapes with little spatial heterogeneity, such as metacommunities following the neutral or patch sorting paradigms. The output metrics from joint species distribution modelling yielded generally the highest resolution to disentangle among the simulated scenarios. Yet, the different types of statistical approaches utilized in this study carried complementary information, and thus our results suggest that the most comprehensive evaluation of metacommunity structure can be obtained by combining them.     

The influence of dispersal on the realized trajectory of a pond metacommunity

Dispersal rates play a critical role in metacommunity dynamics, yet few studies have attempted to characterize dispersal rates for the majority of species in any natural community. Here we evaluate the relationship between the abundances of 179 plankton taxa in a pond metacommunity and their dispersal rates. We find the expected positive relationship between the regional abundances of phytoplankton, protozoa and metazoan zooplankton, which is suggestive of dispersal being a density‐independent per capita rate for these groups. When we tested to see if the rates of dispersing taxa predicted changes in community composition, we found that dispersers had no measurable impact on the short‐term trajectory of local pond communities or mesocosm communities established experimentally (assembled communities), but became increasingly represented in the overall pond metacommunity during the course of the full growing season. In comparison, the composition of experimental mesocosms that lacked any initial zooplankton community (unassembled communities) were found to be driven by dispersal measured at the local pond community but not by dispersal observed across the overall metacommunity. These results suggest that the role of dispersal may shift from a contributor to local, ecological dynamics to that of metacommunity‐wide, colonization–extinction dynamics as communities assemble.     

Species and individual replacements contribute more than nestedness to shape vertebrate scavenger metacommunities

Understanding the mechanisms that organize biodiversity is central in ecology and conservation. Beta diversity links local (alfa) and regional (gamma) diversity, giving insight into how communities organize spatially. Metacommunity ecology provides the framework to interpret regional and local processes interacting to shape communities. However, the lack of metacommunity studies for large vertebrates may limit the understanding and compromise the preservation of ecosystem functions and services. We aim to understand the mechanisms underlying differences in species composition among vertebrate scavenger communities ? which provide key ecosystem functions, e.g. carrion consumption ? within a metacommunity context. We obtained species richness and abundances at scavenger communities consuming ungulate carcasses monitored through motion‐triggered remote cameras in seven terrestrial ecosystems in Spain. We partitioned beta diversity to decompose incidence‐based (species presence/absence) and abundance‐based dissimilarities into their components (turnover/balanced variation and nestedness/abundance gradient, respectively). We identified the environmental factors explaining the observed patterns. The vertebrate scavenger metacommunity consisted of 3101 individuals from 30 species. Changes in composition among ecosystems were mostly (> 84%) due to species or individual replacement (i.e. turnover or balanced variation). Species or individual loss/gain (i.e. nestedness or abundance gradient) accounted for 13–16% of these changes. Mean carcass weight, elevation and habitat diversity were the main factors explaining species/individual replacement. Our findings suggest that local processes such as species‐sorting through habitat heterogeneity would dominate scavenger metacommunity dynamics together with stochastic forces (i.e. related to carrion unpredictability and scavenging being a widespread strategy among vertebrates). The presence of structured patterns (i.e. nestedness) in beta diversity could reflect a role of deterministic processes: mass‐effects through dispersal and defaunation. Vultures are long‐distance foragers and functionally dominant species, which would connect local assemblages within the metacommunity, supporting scavenger diversity and functions across space. These results highlight the importance of managing vertebrate scavenger assemblages within a metacommunity context.     

Ecological consequences of evolution in plant defenses in a metacommunity

Dispersal can affect the assembly of local communities in a metacommunity as well as evolution of local populations in a metapopulation. These two processes may also affect each other in ways that have not yet been well studied and that may have novel effects on community structure. Here, we illustrate the interaction of these two processes on community structure with a model of adaptive evolutionary dynamics of plant defenses in a metacommunity food web involving multiple patches along a productivity gradient. We find an enhanced suite of adaptive plant types in our metacommunity model than is predicted in the absence of dispersal. We also find that this, and the movement of nutrients among patches via dispersal, alters patterns of food web architecture, trophic structure and diversity along the productivity gradient. Overall, our model illustrates that evolutionary and metacommunity dynamics may influence communities in complex interactive ways that may not be predicted by models that ignore either of these types of processes.     

Movement‐mediated community assembly and coexistence

Organismal movement is ubiquitous and facilitates important ecological mechanisms that drive community and metacommunity composition and hence biodiversity. In most existing ecological theories and models in biodiversity research, movement is represented simplistically, ignoring the behavioural basis of movement and consequently the variation in behaviour at species and individual levels. However, as human endeavours modify climate and land use, the behavioural processes of organisms in response to these changes, including movement, become critical to understanding the resulting biodiversity loss. Here, we draw together research from different subdisciplines in ecology to understand the impact of individual‐level movement processes on community‐level patterns in species composition and coexistence. We join the movement ecology framework with the key concepts from metacommunity theory, community assembly and modern coexistence theory using the idea of micro–macro links, where various aspects of emergent movement behaviour scale up to local and regional patterns in species mobility and mobile‐link‐generated patterns in abiotic and biotic environmental conditions. These in turn influence both individual movement and, at ecological timescales, mechanisms such as dispersal limitation, environmental filtering, and niche partitioning. We conclude by highlighting challenges to and promising future avenues for data generation, data analysis and complementary modelling approaches and provide a brief outlook on how a new behaviour‐based view on movement becomes important in understanding the responses of communities under ongoing environmental change.     

Species abundance distribution and dynamics in two locally coupled communities

This study considered a model for species abundance dynamics in two local community (or islands) connected to a regional metacommunity. The model was analyzed using continuous probabilistic technique that employs Kolmogorov-Fokker-Planck forward equation to derive the probability density of the species abundance in the two local communities. Using this technique, we proposed a classification for the species abundance dynamics in the local communities. This classification was made based on such characteristics as immigration intensity, species representation in the metacommunity and the size of local communities. We further distinguished several different scenarios for species abundance dynamics using different ecological characteristics such as species persistence, extinction and monodominance in one or both local communities. The similarity of the species abundance distributions between the two local communities was studied using the correlation coefficient between species abundances in two local communities. The correlation is a function of migration rates between local communities and between local and metacommunity. Immigration between local communities drives the homogenization of the local communities, while immigration from the metacommunity will differentiate them. This community subdivision model provides useful insights for studying the effect of landscape fragmentation on species diversity.     

Empirical approaches to metacommunities: a review and comparison with theory

Metacommunity theory has advanced understanding of how spatial dynamics and local interactions shape community structure and biodiversity. Here, we review empirical approaches to metacommunities, both observational and experimental, pertaining to how well they relate to and test theoretical metacommunity paradigms and how well they capture the realities of natural ecosystems. First, we show that the species-sorting and mass-effects paradigms are the most commonly tested and supported paradigms. Second, the dynamics observed can often be ascribed to two or more of the four non-exclusive paradigms. Third, empirical approaches relate only weakly to the concise assumptions and predictions made by the paradigms. Consequently, we suggest major avenues of improvement for empirical metacommunity approaches, including the integration across theoretical approaches and the incorporation of evolutionary and meta-ecosystem dynamics. We hope for metacommunity ecology to thereby bridge existing gaps between empirical and theoretical work, thus becoming a more powerful framework to understand dynamics across ecosystems.