Partição dos componentes da diversidade beta do fitoplâncton em reservatórios do semiárido: Efeitos da precipitação em diferentes escalas espaciais

Abstract

Due to its high dispersal capacity, the phytoplankton community was not considered a community that could be studied at different scales, and its studies in the semiarid region prioritized sampling at a local scale (within the reservoirs) and, very rarely, considering it as a metacommunity. that, as a result of precipitation, are carried out in these environments. Our objective was to evaluate the influence of spatial-temporal variation of precipitation on beta diversity and its components (substitution and difference in richness) of the phytoplankton community of semiarid reservoirs at different spatial scales. Our hypotheses are (i) that the response of the phytoplankton community to precipitation varies with the spatial scale studied, so that, at the local scale (within the reservoirs), beta diversity increases with precipitation and is mainly explained by the species substitution component . While, on a regional scale (between reservoirs and between mesoregions), there is a reduction in beta diversity and the difference in richness is prevalent; (ii) that precipitation reduces the relative importance of spatial factors in the structuring of the phytoplankton community on the broader scales studied. For this, we investigated fourteen reservoirs distributed in the Planalto da Borborema in two climatic mesoregions (Borborema humid and Borborema seca), in the rainy and dry seasons. To evaluate the partitioned diversity, a hierarchical scheme was elaborated, whose α represents the diversity of the sampling units, β1 the diversity between the sampling units (sites), β2 the diversity between the reservoirs in each mesoregion and β3 the diversity between the mesoregions. We observed that precipitation caused significant effects on the beta diversity of the phytoplankton community and that these effects varied with the spatial scale studied, however, with greater beta diversity at the local scale in the dry season. In addition, we confirmed that precipitation acted by increasing species replacement on a local scale. We also observed that precipitation reduced the importance of spatial factors in the structuring of the phytoplankton community in the dry Borborema scale, however, the importance was greater at the Borborema Plateau and wet Borborema levels during the rainy season. We conclude that the presence of cyanobacteria is not able to reduce the diversity at a local scale in the dry season in our study and spatial factors helped in the dispersion in the rainy season on a large scale, with the community governed by mass effects.