Quais fatores governam a riqueza fitoplanctônica de lagos de inundação em um gradiente latitudinal?.

Abstract

Understanding the distribution patterns of species and how local and regional factors drive the structure of communities is crucial to the preservation of biodiversity. The aim of this study was to evaluate the relative contribution of diversity components of phytoplankton (α1, β1, β2) to γ diversity in Brazilian floodplains (FPs). The partition of γ diversity was conducted at three levels: diversity in the lake (α1), variation in species among lakes within each FP (β1) and variation among FPs (β2). We hypothesize that: i) α diversity responds to a latitudinal gradient, being higher in lakes of lower latitude; ii) there is a greater influence of variations among FPs; iii) β1 is influenced by dispersion in the low water period, and by environmental conditions in the high water period; iv) β2 is influenced mainly by dispersion. Phytoplankton samples were taken at the subsurface (depth 20 cm) in limnetic region of each lake, in the low and high water in 2011 and 2012. Principal Component Analysis was performed to summarize the environmental variability and Partial Redundancy Analysis (pRDA) to evaluate the influence of dispersion and environmental factors on richness. Significant environmental differences were evidenced between FPs. The greater γ diversity occurred in the FPs of the Araguaia and Amazon. The high contribution of β1 for γ diversity revealed the high environmental heterogeneity in FPs. β1 was more influenced by environmental and β2 by both fractions. Different degrees of connectivity facilitated the dispersal and colonization of phytoplankton organisms. The γ diversity was explained by the interaction between local and regional factors that are correlated with the latitude and not only by latitude itself.