The metacommunity concept has the potential to integrate local and regional dynamics within a general community ecology framework. To this end, the concept must move beyond the discrete archetypes that have largely defined it (e.g. neutral vs. species sorting) and better incorporate local scale species interactions and coexistence mechanisms. Here, we present a fundamental reconception of the framework that explicitly links local coexistence theory to the spatial processes inherent to metacommunity theory, allowing for a continuous range of competitive community dynamics. These dynamics emerge from the three underlying processes that shape ecological communities: (1) density-independent responses to abiotic conditions, (2) density-dependent biotic interactions and (3) dispersal. Stochasticity is incorporated in the demographic realisation of each of these processes. We formalise this framework using a simulation model that explores a wide range of competitive metacommunity dynamics by varying the strength of the underlying processes. Using this model and framework, we show how existing theories, including the traditional metacommunity archetypes, are linked by this common set of processes. We then use the model to generate new hypotheses about how the three processes combine to interactively shape diversity, functioning and stability within metacommunities.

Propagule dispersal beyond local scales has been considered rare and unpredictable. However, for many plants, invertebrates, and microbes dispersed by birds, long-distance dispersal (LDD) might be regularly achieved when mediated by migratory movements. Because LDD operates over spatial extents spanning hundreds to thousands of kilometers, it can promote rapid range shifts and determine species distributions. We review evidence supporting this widespread LDD service and propose a conceptual framework for estimating LDD by migratory birds. Although further research and validation efforts are still needed, we show that current knowledge can be used to make more realistic estimations of LDD mediated by regular bird migrations, thus refining current predictions of its ecological and evolutionary consequences.

Statement of authorship:This project was conceived at the sTURN working group, of which all authors are members. PLT developed the framework and model with input from all authors. PLT wrote the model code. PLT and LMG performed the simulations. PLT produced the figures and wrote the first draft with input from LMG and JMC. All authors provided feedback and edits on several versions of the manuscript. Data accessibility:All code for running the simulation model and producing the figures will be archived on Zenodo upon acceptance and the doi will be included at the end of the manuscript. AbstractThe metacommunity concept has greatly advanced our understanding of how spatial dynamics shape ecological communities. To date, this framework has emphasized discrete differences between mechanisms structuring metacommunities (e.g. niche vs. neutral), despite the recognition that assembly processes are continuous. Here we present a fundamental reconception of the framework that explicitly links local coexistence theory to metacommunity theory and allows for a continuous range of competitive metacommunity dynamics. These dynamics emerge from the underlying processes that shape the dynamics of ecological communities: 1) density-independent responses to abiotic conditions, 2) density-dependent biotic interactions, and 3) dispersal. We also incorporate stochasticity in the demographic realization of each of these processes. The traditional metacommunity archetypes exist as discrete regions within this space, but our framework highlights a range of dynamics that are missed in classic metacommunity theory. We formalize this framework using a simulation model that explores the full range of competitive metacommunity dynamics by varying the strength of the underlying processes. We illustrate how the different processes interactively shape the diversity, functioning, and stability of metacommunities. This process-based framework extends the rich history of metacommunity ecology and can be used to generate testable hypotheses on the processes structuring metacommunities in nature.

Niche and neutral processes drive community assembly and metacommunity dynamics, but their relative importance might vary with the spatial scale. The contribution of niche processes is generally expected to increase with increasing spatial extent at a higher rate than that of neutral processes. However, the extent to what community composition is limited by dispersal (usually considered a neutral process) over increasing spatial scales might depend on the dispersal capacity of composing species. To investigate the mechanisms underlying the distribution and diversity of species known to have great powers of dispersal (hundreds of kilometres), we analysed the relative importance of niche processes and dispersal limitation in determining beta‐diversity patterns of aquatic plants and cladocerans over regional (up to 300 km) and continental (up to 3300 km) scales. Both taxonomic groups were surveyed in five different European regions and presented extremely high levels of beta‐diversity, both within and among regions. High beta‐diversity was primarily explained by species replacement (turnover) rather than differences in species richness (i.e. nestedness). Abiotic and biotic variables were the main drivers of community composition. Within some regions, small‐scale connectivity and the spatial configuration of sampled communities explained a significant, though smaller, fraction of compositional variation, particularly for aquatic plants. At continental scale (among regions), a significant fraction of compositional variation was explained by a combination of spatial effects (exclusive contribution of regions) and regionally‐structured environmental variables. Our results suggest that, although dispersal limitation might affect species composition in some regions, aquatic plant and cladoceran communities are not generally limited by dispersal at the regional scale (up to 300 km). Species sorting mediated by environmental variation might explain the high species turnover of aquatic plants and cladocerans at regional scale, while biogeographic processes enhanced by dispersal limitation among regions might determine the composition of regional biotas.

BackgroundMosquito feeding behaviour determines the degree of vector–host contact and may have a serious impact on the risk of West Nile virus (WNV) epidemics. Feeding behaviour also interacts with other biotic and abiotic factors that affect virus amplification and transmission.Methodology/Principal FindingsWe identified the origin of blood meals in five mosquito species from three different wetlands in SW Spain. All mosquito species analysed fed with different frequencies on birds, mammals and reptiles. Both ‘mosquito species’ and ‘locality’ explained a similar amount of variance in the occurrence of avian blood meals. However, ‘season of year’ was the main factor explaining the presence of human blood meals. The differences in diet resulted in a marked spatial heterogeneity in the estimated WNV transmission risk. Culex perexiguus, Cx. modestus and Cx. pipiens were the main mosquito species involved in WNV enzootic circulation since they feed mainly on birds, were abundant in a number of localities and had high vector competence. Cx. perexiguus may also be important for WNV transmission to horses, as are Cx. pipiens and Cx. theileri in transmission to humans. Estimates of the WNV transmission risk based on mosquito diet, abundance and vector competence matched the results of previous WNV monitoring programs in the area. Our sensitivity analyses suggested that mosquito diet, followed by mosquito abundance and vector competence, are all relevant factors in understanding virus amplification and transmission risk in the studied wild ecosystems. At some of the studied localities, the risk of enzootic circulation of WNV was relatively high, even if the risk of transmission to humans and horses was less.Conclusions/SignificanceOur results describe for first time the role of five WNV candidate vectors in SW Spain. Interspecific and local differences in mosquito diet composition has an important effect on the potential transmission risk of WNV to birds, horses and humans.

Long distance dispersal (LDD) of propagules is an important determinant of population dynamics, community structuring and biodiversity distribution at landscape, and sometimes continental, scale. Although migratory animals are potential LDD vectors, migratory movement data have never been integrated in estimates of propagule dispersal distances and LDD probability. Here we integrated migratory movement data of two waterbird species (mallard and teal) over two continents (Europe and North America) and gut retention time of different propagules to build a simple mechanistic model of passive dispersal of aquatic plants and zooplankton. Distance and frequency of migratory movements differed both between waterbird species and continents, which in turn resulted in changes in the shapes of propagule dispersal curves. Dispersal distances and the frequency of LDD events (generated by migratory movements) were mainly determined by the disperser species and, to a lesser extent, by the continent. The gut retention time of propagules also exerted a significant effect, which was mediated by the propagule characteristics (e.g. seeds were dispersed farther than Artemia cysts). All estimated dispersal curves were skewed towards local‐scale dispersal and, although dispersal distances were lower than previous estimates based only on the vector flight speed, had fat tails produced by LDD events that ranged from 230 to 1209 km. Our results suggest that propagule dispersal curves are determined by the migratory strategy of the disperser species, the region (or flyway) through which the disperser population moves, and the propagule characteristics. Waterbirds in particular may frequently link wetlands separated by hundreds of kilometres, contributing to the maintenance of biodiversity and, given the large geographic scale of the dispersal events, to the readjustment of species distributions in the face of climate change.

Migratory birds are often suggested to be important vectors for long-distance dispersal (LDD) of plant and animal propagules. The scale of such dispersal events (hundreds to thousands of kilometers) can influence landscape-level biological processes and species distributions. However, the few vector species studied and the lack of proper integration of their migratory movement in models of LDD has precluded the study of their potential as long-distance biotic dispersers. By means of a mechanistic model parameterized with empirical data, we first investigated the properties of seed dispersal curves generated by migratory birds and then analyzed the effect of bird size on model parameters and consequent seed dispersal patterns. Seed dispersal curves showed in most cases large and heavy tails, resulting in relatively frequent LDD (up to 3.5% of dispersal distances longer than 100 km). Bird size mediated trade-offs between bird movement and seed retention time that, in turn, determined seed dispersal patterns and the potential of each bird species as an LDD vector. Our modeling framework builds on a mechanistic understanding of seed dispersal by migratory birds and may thus be a useful tool to estimate the scale and frequency of bird-mediated, large-scale transport of native, invasive, and pathogenic organisms.

The abundance and distribution of species across the landscape depend on the interaction between local, spatial, and stochastic processes. However, empirical syntheses relating these processes to spatiotemporal patterns of structure in metacommunities remain elusive. One important reason for this lack of synthesis is that the relative importance of the core assembly processes (dispersal, selection, and drift) critically depends on the spatial grain and extent over which communities are studied. To illustrate this, we simulated different aspects of community assembly on heterogeneous landscapes, including the strength of response to environmental heterogeneity (inherent to niche theory) vs. dispersal and stochastic drift (inherent to neutral theory). We show that increasing spatial extent leads to increasing importance of niche selection, whereas increasing spatial grain leads to decreasing importance of niche selection. The strength of these scaling effects depended on environment configuration, dispersal capacity, and niche breadth. By mapping the variation observed from the scaling effects in simulations, we could recreate the entire range of variation observed within and among empirical studies. This means that variation in the relative importance of assembly processes among empirical studies is largely scale dependent and cannot be directly compared. The scaling coefficient of the relative contribution of assembly processes, however, can be interpreted as a scale‐integrative estimate to compare assembly processes across different regions and ecosystems. This emphasizes the necessity to consider spatial scaling as an explicit component of studies intended to infer the importance of community assembly processes.