The metacommunity framework has greatly advanced our understanding about the importance of local and regional processes structuring ecological communities. However, information on how metacommunity structure and the relative strengths of their underlying mechanisms change through time is largely lacking. Dynamic systems that undergo environmental temporal changes and disturbances, such as floodplains, serve as natural laboratories to explore how their metacommunity structure change in time. Here we applied the Elements of Metacommunity Structure framework and variation partitioning analysis to assess how temporal changes in the local environmental factors and regional dispersal processes in the rain season influence a seasonal floodplain‐fish metacommunity. Across four months, relevant environmental factors were measured across 21 patches where over 3500 individual fish were sampled. Connectivity was measured using landscape resistance‐based metrics and additional spatial variation in metacommunity structure was assessed via spatial autocorrelation functions. The metacommunity structure changed from nestedness, at the beginning of the flood season, to a quasi‐Clementsian gradient at the end. Our analyses show that connectivity is only important in the beginning of the flood season whereas environment is only important at the end. These results suggest that this metacommunity is structured by changes between dispersal limitation and environmental filtering through time.

Ecological communities show extremely complex patterns of variation in space, and quantifying the relative importance of spatial and environmental factors underpinning patterns of species distributions is one of the main goals of community ecology. Although we have accumulated good knowledge about the processes driving species distributions within metacommunities, we have few insights about whether (and how) environmental and spatial features can actually generate consistent species distributional patterns across multiple metacommunities. In this paper we applied the elements of metacommunity structure (EMS) framework to identify and classify metacommunities according to multiple but discrete patterns of species distributions. Given that each pattern has unique underlying structuring mechanisms, exploring and comparing such patterns across multiple metacommunities spanning large geographical areas provides a way to test the existence of general principles underlying species distributions within metacommunities. In this study, we applied the EMS framework into a data set containing about 9000 lakes distributed across 85 fish metacommunities across Ontario, Canada, and estimated the relative importance of local and spatial factors in explaining their distributional patterns. Nested and Clementsian gradients were the patterns that fitted most metacommunities; nested metacommunities were distributed throughout the province, while Clementsian gradient metacommunities were concentrated in the southeastern region. Sixty-five percent of nested metacommunities were located in low-energy watersheds (i.e., colder climate and shorter growing season), whereas metacommunities representing Clementsian gradients were present in high-energy watersheds (i.e., relatively warmer climate and longer growing season). Taken together, our results reveal that the environmental and spatial properties in which metacommunities are embedded are at least partially responsible for their species distributional patterns.

The hierarchical branching nature of river networks can have a strong influence on the assembly of freshwater communities. This unique structure has spurred the development of the network position hypothesis (NPH), which states that the strength of different assembly processes depends on the community position in the river network. Specifically, it predicts that 1) headwater communities should be exclusively controlled by the local environment given that they are more isolated and environmentally heterogeneous relative to downstream reaches. In contrast, 2) downstream communities should be regulated by both environmental and dispersal processes due to increased connectivity given their central position in the riverscape. Although intuitive, the NPH has only been evaluated on a few catchments and it is not yet clear whether its predictions are generalizable. To fill this gap, we tested the NPH on river dwelling fishes using an extensive dataset from 28 French catchments. Stream and climatic variables were assembled to characterize environmental conditions and graph theory was applied on river networks to create spatial variables. We tested both predictions using variation partitioning analyses separately for headwater and downstream sites in each catchment. Only 10 catchments supported both predictions, 11 failed to support at least one of them, while in 7 the NPH was partially supported given that spatial variables were also significant for headwater communities. We then assembled a dataset at the catchment scale (e.g. topography, environmental heterogeneity, network connectivity) and applied a classification tree analysis (CTA) to determine which regional property could explain these results. The CTA showed that the NPH was not supported in catchments with high heterogeneity in connectivity among sites. In more homogeneously connected catchments, the NPH was only supported when headwaters were more environmentally heterogeneous than downstream sites. We conclude that the NPH is context dependent even for taxa dispersing exclusively within streams.

Dispersal has long been recognized as a mechanism that shapes many observed ecological and evolutionary processes. Thus, understanding the factors that promote its evolution remains a major goal in evolutionary ecology. Landscape connectivity may mediate the trade-off between the forces in favour of dispersal propensity (e.g. kin-competition, local extinction probability) and those against it (e.g. energetic or survival costs of dispersal). It remains, however, an open question how differing degrees of landscape connectivity may select for different dispersal strategies. We implemented an individual-based model to study the evolution of dispersal on landscapes that differed in the variance of connectivity across patches ranging from networks with all patches equally connected to highly heterogeneous networks. The parthenogenetic individuals dispersed based on a flexible logistic function of local abundance. Our results suggest, all else being equal, that landscapes differing in their connectivity patterns will select for different dispersal strategies and that these strategies confer a long-term fitness advantage to individuals at the regional scale. The strength of the selection will, however, vary across network types, being stronger on heterogeneous landscapes compared with the ones where all patches have equal connectivity. Our findings highlight how landscape connectivity can determine the evolution of dispersal strategies, which in turn affects how we think about important ecological dynamics such as metapopulation persistence and range expansion.

Aim We investigated how freshwater microcrustaceans with different susceptibilities to Allee effects differ in the distribution of their geographical range size (GRS) and diversity along latitudinal gradients, evaluating the importance of climatic and historical factors in explaining these differences. We hypothesized that sexual copepods would have a smaller GRS and that their distribution would be linked to historical processes due to mate‐finding Allee effects during colonization. Given that cyclic parthenogenetic cladocerans avoid these Allee effects, we predicted that they would exhibit a larger GRS and their distribution would be related to climatic factors rather than dispersal limitation. Location Canadian watersheds, North America. Methods We used a database containing the presence–absence of freshwater zooplankton across 1665 Canadian lakes along a latitudinal gradient of 40°. We computed GRS using minimum convex polygons encompassing all lakes in which each species was present. We pooled the diversity of lakes within watersheds, and computed linear regressions models between watershed diversity and average GRS with the average latitude, distance from a glacial refugium and environmental variables of the watershed. All analyses were performed separately for cladocerans and copepods. Results Cladocerans exhibited, on average, a GRS 70% larger than that of copepods. We found a strong relationship between diversity (negative) and average GRS (positive) with latitude for cladocerans but not for copepods. Cladoceran macroecological patterns were mainly explained by climatic factors, whereas the lack of latitudinal gradients in copepods was potentially due to the influence of a northern glacial refuge and dispersal limitation. Main conclusions Our results show that Allee effects are strongly and negatively associated with GRS, influencing the relative importance of environmental filtering and dispersal limitation on species diversity patterns. We suggest that studies should avoid lumping species with large differences in their susceptibility to Allee effects in order to better disentangle the multiple processes affecting large‐scale patterns.