Influence of past and current factors on the beta diversity of coastal lagoon fish communities in South America

Aim: We aimed to assess the relative influence of past (Quaternary
paleodrainage characteristics) and current factors on the beta diversity
of freshwater fishes in coastal lagoons and explore the main processes
involved. Location: Atlantic coast of South America. Taxon: Fishes (173
species) Methods: We built a dataset of species occurrence in 129 lagoons
across eight freshwater ecoregions of the world (FEOWs) located between
latitudes 0° and 36° and calculated beta diversity (βjac) and its turnover
(βjtu) and nestedness (βjne) components. We used a partial Mantel test and
multiple regressions on distance matrices to evaluate the importance of
past and current factors, and of geographical distance in determining beta
diversity. Past variables were those representing the historical
freshwater habitat during the last glacial maximum (LGM), and contemporary
variables were those related to current habitat. Results: We found high
values of βjac within the FEOWs, with βjtu prevailing over βjne. Both past
(paleodrainage) and current (drainage area, salinity, and lagoon area)
factors affected species dissimilarity (βjac = 46%) and its components
(βjtu = 44% and βjne =20%), although explanation was, in part, shared with
geographical distance. Individually, the influence of past factors was
prevalent in beta diversity and its components. Main Conclusions: The
results suggest that major changes in the availability of freshwater
habitats and connectivity since the Pleistocene must have affected the
colonization, extinction and recolonization processes of fishes along the
eastern coast of South America. We suggest that the high beta diversity
values may result from limited dispersal after extinctions in the LGM and
that the dissimilar freshwater fish communities currently seen were formed
mainly by heterogeneous subsets of the regional species pool that
persisted in landscape refuges during past sea level increases and then
recolonized coastal lagoons.