Habitat and landscape factors associated with the nestedness of waterbird assemblages and wetland habitats in South Brazil

Abstract The recognition of patterns in metacommunities and the elucidation of the processes responsible for them are major goals of community ecology. The nestedness of local communities based on species occurrence was initially postulated as resulting from selective extinction – species‐poor sites are subsets of species‐rich sites. Alternative mechanisms that could generate this pattern include passive sampling, selective colonization and habitat nestedness. In this study, we investigated the nestedness of waterbird assemblages in 42 wetland remnants and the mechanisms behind this pattern. Specifically, the following expectations were tested: (i) that waterbird species in wetland remnants are distributed in a nested fashion; (ii) that microhabitats created by macrophyte banks are distributed in wetland remnants in a nested fashion; (iii) that the nestedness of the waterbird assemblage is associated with the size, isolation and nestedness of microhabitats; (iv) that the rank of species in the assemblage can be explained by biological attributes associated with vulnerability to habitat loss and fragmentation; (v) that species that deviate from the nested pattern have peculiar biological attributes. We recorded the presence of 55 waterbird species in 12 monthly censuses over 1 year. The waterbird metacommunity was significantly nested when ordered independently by species richness, fragment area, microhabitat diversity and isolation. The microhabitats were also nested. Partial correlations and linear regression revealed a strong association of the rank of sites with area and isolation. Twenty‐one waterbird species were considered idiosyncratic. Species with large body size and low sensitivity to disturbance showed greater probability of being idiosyncratically distributed. We conclude that the waterbird assemblages are nested as a consequence of selective extinction and selective colonization. Species that deviate from the nested pattern tend to have large body size and low sensitivity to human disturbance. The study emphasizes the importance of focusing conservation efforts on large wetland remnants and their degree of isolation and human perturbation.