Emergence of the metacommunity concept has made a substantial contribution to better understanding of the community composition and dynamics in a regional context. However, long‐term field data for testing of available metacommunity models are still scarce, and the extent to which these models apply to the real world remains unknown. Tests conducted so far have largely sought to fit data on the entire regional set of species to one of several metacommunity models, implicitly assuming that all species operate similarly over the same set of sites. However, species differ in their habitat use. These differences can, in the most general terms, be expressed as a gradient of habitat specialization (ranging from habitat specialists to habitat generalists). We postulate that such differences in habitat specialization will have implications for metacommunity dynamics. Specifically, we predict that specialists respond more to local processes and generalists respond to regional spatial processes. We tested these predictions using natural microcosm communities for which long‐term (nine‐year) environmental and population dynamics data were available. We used redundancy analysis to determine the proportion of variation explained by environmental and spatial factors. We repeated this analysis to explain variation in the entire regional set of species, in generalist species only, and in specialists only. We further used ANOVA to test for differences in the proportions of explained variation. We found that habitat specialists responded primarily to environmental factors and habitat generalists responded mainly to spatial factors. Thus, from the metacommunity perspective, the dynamics of habitat specialists are best explained by a combination of species sorting and mass effects, while that of habitat generalists are best explained by patch dynamics and neutral models. Consequently, we infer that a natural metacommunity can exhibit complicated dynamics, with some groups of species (e.g., habitat specialists) governed according to environmental processes and other groups (e.g., habitat generalists) governed mainly by dispersal processes.

Metacommunity perspective highlights the role of space as a factor contributing to local community structure and dynamics. Often tests of metacommunity models rely on snapshot patterns of species distribution and abundance. Such patterns may introduce biases because they overlook differences in responses of constituent species to changing environmental conditions, particularly when such responses override patterns predicted from dispersal and biotic interactions alone. This applies, for example, to habitat generalists, whose responses to environmental variations differ from those of habitat specialists, resulting in different snapshot patterns at different times. Synchronized (i.e., correlated among sites) environmental variation is perhaps the most obvious case of environmental variation that could generate regular differences among species of different specialization. We hypothesized that synchronized environmental variation synchronizes local populations of habitat specialists to a greater degree than it does for habitat generalists as experiments have shown that habitat generalists are less sensitive to changing environmental conditions. To test this in an empirical system, we used time series data (nine annual surveys) on an invertebrate metacommunity of 49 rock pools on the coast of Jamaica. We found that population synchrony of a significant portion of 24 species sharing these rock pools increased with habitat specialization in response to environmental synchrony (represented by synchrony of environment). However, distance among rock pools, which may affect dispersal or shared perturbations, was negatively correlated with population synchrony of individual species, irrespective of their specialization. As only habitat specialists showed increasing synchrony with environmental synchrony, and both generalist and specialist synchrony were negatively correlated with distance, we infer that habitat generalists must be synchronized more by space‐related processes while habitat specialists by a combination of environmental forcing and dispersal. Overall, the study suggests that species of different habitat specialization show consistent differences with respect to local processes involving environmental variations but show fewer differences with respect to regional processes involving distance, at least when long‐term dynamics are concerned. Furthermore, the study identifies a rarely recognized link between variation in space and its consequences for variation in time—a link much more expressed among spatially restricted species such as habitat specialists.

Urbanization often leads to the homogenization of species composition in aquatic ecosystems, as it introduces disturbances that can destroy the habitats of unique endemic or native species while creating alternative habitats for species capable of adapting to these conditions. This study utilized a long-term dataset from 1971 to 2010, focusing on fish species presence within three watersheds of the Greater Toronto Area, Canada. The objective was to evaluate any changes in fish communities over time across three groups of species assemblages: native, non-native species, and a combining of all species. We considered key predictor variables for which data exist: catchment area, distance to a species pool source (Lake Ontario), and percentage of urban cover, to determine their impacts on species richness over time. Three hypotheses were tested: (1) the rate of change in species richness differs among the three groups; (2) urbanization promotes the spread and homogenization of non-native species distribution; and (3) native species assemblages exhibit high nestedness initially, decreasing over time as non-native species established and replaced native species. We used general linear models and the nestedness analysis to characterize matrices of species distributions of native and non-native fish assemblages among the catchments over time. Overall, the results indicate that nestedness temperatures (NTs) for native fish were lower compared to non-native fish assemblages. Over the four decades studied, native species richness declined with increasing urban cover, while non-native species richness increased and compensated for native losses. Furthermore, native species assemblages exhibited high nestedness at the beginning of the record period, which decreased over time as non-native species became established and replaced native species. This trend suggests that further changes in fish communities are probable. As native fish communities become patchier (not nested), this process may accelerate, potentially isolating communities and making them more prone to perturbations.