PS 60-26
Implications beyond metacommunity dynamic theory in a highly diverse tropical system: distinct responses in habitat-generalists and specialists stream fish
A complex suite of environmental and spatial factors influence stream fish metacommunities. Metacommunity dynamics can differ among group of species according to their degree of specialization. For instance, fish explore instream habitat in different ways and species may be classified as habitat-generalists (exploring water column or marginal pools, without dependence of rocky or woody elements) or habitat-specialists (exploring water surface, bottom or marginal microhabitats, often with rocky or woody elements). Our hypothesis is that environmental variables would explain a higher proportion of the variation in the spatial distribution of habitat-specialist species, whereas spatial variables would be relatively more important for habitat-generalists species. To test this, we investigated the relative influence of environmental and/or spatial variables to test the four metacommunity paradigms (species sorting, mass-effect, neutral model, and patch dynamics) and determined the drivers for these paradigms for the three sub-sets of species, using composition and abundances matrices. We used data sets of 139 species from 75 stream reaches in a sub-basin of the Madeira River system, a highly diverse basin in western Amazon, and used the partial Redundancy Analysis to assess the proportion of variation explained by environmental and spatial variables in each species group.
Results/Conclusions
All axes that represent species ordinations were significantly explained by local and landscape variables. Along the first axis of each ordination diagram we also detected a conservation gradient (from preserved to degraded sites), each one with different species associations. Species composition and abundance are structured according to species sorting and mass effect models, revealing that environment and space are important for species community structure. The drivers for species sorting were the local variables related to vegetation in the riparian buffer (percent of shrubs and of grass), to substrate type in the bottom (percent of silt and of sand); and the landscape variables related to soil type (proportions of oxisol and of ultisol) and land use (proportion of mature forests). The entire fish metacommunity was consistent with the habitat-generalists assemblage and both responded primarily to space. In this case, the proximity to the Madeira River can be viewed as the potential source of upstream colonization that represents the main driver for mass effect. In contrast, the habitat-specialists assemblage responded mainly to environmental variables. With these results, we reinforce the importance of taking into account the habitat requirements of each species to define metacommunity dynamics.