Functional trait sorting increases over succession in metacommunity mosaics of fish assemblages.

Metacommunity theory predicts that the relative importance of regional and local processes structuring communities will change over time since initiation of community assembly. Determining effects of these processes on species and trait diversity over succession remains largely unaddressed in metacommunity ecology to date, yet could confer an improved mechanistic understanding of community assembly. To test theoretical predictions of the increasing importance of local processes in structuring communities over successional stages in metacommunities, we evaluated fish species and trait diversity in three pond metacommunities undergoing secondary succession from beaver (Castor canadensis) disturbance. Processes influencing taxonomic and trait diversity were contrasted across pond communities of different ages and in reference streams. Counter to predictions, the local environment became less important in structuring communities over succession but did exert a stronger effect on trait sorting. Beta diversity and trait richness declined over succession while there was no influence on species richness or trait dispersion. The trait filtering in older habitats was likely a response to the larger and deeper pond ecosystems characteristic of late succession. In contrast to these observed effects in ponds, the local environment primarily structured species and trait diversity in streams. Analyses of the relative importance of regional and local processes in structuring fish assemblages within each pond metacommunity suggests that habitat age and connectivity were more important than the environment in structuring communities but contributions were region and scale-dependent. Together, these findings highlight that regional and local processes can differentially influence taxonomic and trait diversity in successional metacommunity mosaics.