Abstract Stream macroalgal communities were sampled at 58 sites across four national parks representing highland grasslands in southeastern Brazil. We assessed taxonomic beta diversity and its components (spatial turnover and nestedness), as well as the influence of selected environmental variables. Environmental conditions varied widely among streams from the different parks, reflecting high environmental heterogeneity, a pattern commonly reported for similar ecosystems worldwide. Cyanobacteria predominated in the flora of the four parks (47.4%), consistent with previous studies, and most species were heterocytous (81.5%), likely reflecting adaptation to low nitrogen availability. Two general patterns evidenced from the analyses: (1) a positive correlation between species richness with percent cover and the Shannon–Wiener diversity index, indicating that the richest and most abundant communities were also the most diverse, in accordance with the patch dynamics concept; and (2) a strong trend of occurrence of species with restricted distributions, with most taxa recorded in only one park or in a few sites within a single park. Taxonomic beta diversity was extremely high (0.96–0.97), showing that spatial turnover (species replacement) accounted for nearly all the observed variation, while the nestedness component was very low (0.01). Thus, community composition was not structured as subsets of a richer community; instead, differences among communities primarily resulted from species replacement driven by environmental filtering. These findings support our hypothesis that the four national parks function as islands, each isolated and represented by its respective mountain range. This isolation results in comparable levels of alpha diversity within parks but markedly elevated beta diversity among them.
Necchi et al. (Sat,) studied this question.
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