Limnetica 39

Models associating the responses of the plankton community with the metacommunity structure have expanded our understanding of the frequency with which dispersal-related mechanisms are associated with these responses, which depend on the local characteristics of the habitat and the degree of connectivity between habitats. Our study patterns in the phytoplankton community structure of freshwater rock pools in dryland ecosystems of northeast Brazil. We hypothesized that depending on the degree of isolation between rock pools, functional groups would be better indicators of the isolation gradients than would species, with a decrease in the similarity between communities with increasing distance. We sampled 20 rock pools across a region with rainfall < 300 mm/yr (Paraíba, Brazil), and identified 55 taxa in 13 functional groups. Cyanobacteria dominated in 10 of the 20 rock pools, which were shallow (≤1.5 m) and slightly acidic to alkaline (pH 5.8–10.3). The Jaccard similarity index showed no correlation with the distance between rock pools, suggesting that isolation did not influence the species composition, although a highly stochastic distribution was observed. A synergy among local structuring factors (size, depth, light limitation) and spatial (dispersal) factors appears to best explain distribution and structure of the phytoplankton communities in these freshwater rock pools.