Habitat age influences metacommunity assembly and species richness in successional pond ecosystems

Metacommunity theory suggests that species diversity can depend upon the time since initiation of community assembly, or habitat age, as the relative influence of regional and local structuring processes changes over succession. There are, however, few studies that evaluate the role of habitat age in structuring species richness (diversity-age) over large, fine-resolution age gradients of secondary succession in metacommunities. To test theoretical predictions of diversity-age relationships in metacommunities, zooplankton species richness and composition along a successional chronosequence in beaver (Castor canadensis) ponds were evaluated. The age of ponds was determined using dendrochronology and historical photography, and ranged from 23 to 69 yr of age. A unimodal relationship between zooplankton species richness and habitat age was observed among the successional ecosystems. This hump-shaped relationship with community assembly time is congruent with theoretical predictions of species richness in metacommunities and can be explained by the increasing importance of local, relative to regional, structuring processes over successional trajectories. Observed patterns of diversity and composition responded to age-mediated effects on the local pond environment; older ponds were deeper, had lower colored dissolved organic carbon, and were permanent. Additionally, there were weak but significant dispersal effects on community composition across the region. The lack of consistent community composition by successional stage reflected variation from differences in pond nutrient availability and species dispersal. The results indicate that regional and local age-dependent structuring mechanisms operate at each successional stage on different local colonist pools and environments yielding communities that reflect succession in their richness response. Consequently, secondary succession should be considered an influential driver of species diversity across temporal and spatial scales in metacommunities.