Metacommunity assembly and sorting in novel lake communities

Background/Question/Methods   When multiple new habitats are created, community assembly may follow independent trajectories, since the relative importance of dispersal limitation, priority effects, species interactions, and environmental gradients changes as assembly proceeds. Unfortunately, tracking community colonization and composition across decades is challenging. We compiled a multiyear community composition dataset and reconstructed past communities with remains from sediment cores to investigate cladoceran assembly dynamics in six older (1920s) and two more recently formed (1950s) lakes. Using this dataset, we tested for evidence of species sorting in the current metacommunity assemblage. We then asked whether the importance of spatial structure and environmental gradients on community assemblages changed through time. We finally tested for differences in metacommunity assembly between the older and more recently formed lakes.

Results/Conclusions   We found that current communities cluster along a stratification gradient related to predation intensity. Assembling communities showed evidence for a greater influence of species sorting and a reduced influence of spatial structure since the first colonizations. However, lake colonization sequences and community trajectories varied considerably, reflecting the history of early colonizers (priority effects). In the older lakes, small-bodied cladocerans often arrived much earlier than large-bodied cladocerans, while the two younger lakes were colonized much more rapidly, and one was quickly dominated by a large-bodied species. Thus, by combining contemporary community data with paleoecological records, we show that assembly history influences natural community structure for decades while patterns of ecological sorting develop.