Our understanding of how temporal turnover and nestedness (β-diversity) mediate biodiversity change in metacommunities is limited. In principle, variability in species composition may arise from the temporal replacement of species (turnover) or patterns in which time periods (sampling events) with small numbers of species are subsets of time periods with larger species numbers (nestedness). The aquatic habitats of the Amazon are excellent model systems for studying temporal variation in species composition, as they have considerable habitat heterogeneity and host the world’s most diverse freshwater ichthyofauna. Here we ask whether species turnover (but not necessarily greater nestedness) is greater – as predicted by β-diversity theory – in more interconnected large rivers and floodplain systems than in less interconnected terra firme streams and upland Shield streams. To test this hypothesis, we sampled the fish of all four habitat types every two months for one year (with each habitat replicated at two sites). We derived measures of temporal β-diversity between pairs of successive (temporally adjacent) sampling events and used generalized linear models to compare patterns of temporal species turnover and nestedness in each habitat type.
2) Results/Conclusions
Consistent with our hypothesis, we observed significantly greater temporal species turnover through the annual hydrological cycle in large river and floodplain systems than in terra firme streams and shield streams. However, we found no significant difference in nestedness between the four habitat-types. Large Amazon rivers and adjacent seasonally inundated floodplains exhibit minimal structural/chemical barriers to long-distance dispersal. In contrast, terra firme streams exhibit potential barriers to fish immigration and emigration in the form of discontinuities in habitat structure as well as thermal/chemical gradients with the river-floodplain systems they drain into. Upland shield streams are further isolated from their lower terra-firme stream courses by waterfalls. Our analyses support the hypothesis that structural connectivity and flood regime influence temporal species turnover and validate the notion that relative connectivity/isolation between metacommunities governs dispersal limitations.