Dispersão de macroinvertebrados em estuários tropicais: Uma análise a partir de múltiplas escalas

Abstract

Dispersion is one of the main factors that contribute in the communities assembly, being extremely important in the processes of colonization and recolonization of ecosystems. Dispersion can be divided into passive dispersion when it is governed by external factors, and active dispersion, when it is dependent on the intrinsic characteristics of the organisms. There is a gap in knowledge about dispersal of macroinvertebrates in estuarine ecosystems, mainly about which factors (environmental or spatial) influence the distribution of dispersive characteristics. Thus, we tested the hypotheses: i) the functional dispersive categories contribute to a higher functional beta diversity in typical tropical estuaries, and a higher alpha diversity in semi-arid tropical estuaries, due to the greater and lesser longitudinal environmental dynamics of these ecosystems, respectively; ii) during the period of greater precipitation, the functional dispersive traits contributed to a lower beta diversity; and iii) the shared environment (environmental and spatial factors) influences the distribution of dispersive functional traits of benthic macroinvertebrates in typical tropical estuaries, while only environmental variables influence dispersive traits in semi-arid estuaries. To test the hypotheses, we evaluated three estuaries located in a typical tropical region and three estuaries located in a region with a semi-arid tropical climate, in periods of high and low precipitation. We evaluated the dispersive functional traits of the most representative groups of benthic macroinvertebrates in the community, polychaetas and molluscs. With this, we selected four dispersive functional traits, with 14 categories: larval development, fecundity, body size and mobility. To evaluate the distribution of dominance of the dispersive functional traits across estuaries, we calculated a Community-Weighted Means (CWM). Significant spatial and seasonal differences were tested using Permutation Analysis of Variance (PERMANOVA). To evaluate the average dissimilarity between pairs of functional traits according to the dispersal modes of benthic macroinvertebrates at multiple spatial scales, we used Rao's quadratic entropy index. We evaluated the effect of environmental and spatial variables on dispersive traits with Partial Redundancy Analysis (pRDA). The results of the functional partition of diversity showed that both types of estuaries showed the same trend of high alpha diversity in both seasonal periods. This result demonstrates greater dissimilarity within sites than between sites sampled, resulting in the coexistence of organisms with different functional traits. When we analyze the effect of environmental and spatial variables on dispersive functional categories, we find that typical tropical estuaries are seasonally influenced by both environmental and space factors. This is due to the clear longitudinal environmental gradient in these estuaries, providing that near regions are more similar and appropriate for functionally similar taxa. On the other hand, the semi-arid estuaries showed a seasonal difference in the relationship between the environment and/or space as a function of dispersive functional traits, demonstrating that temporal changes affected the dispersive dynamics of organisms in these types of estuaries. Therefore, we observed that there was a greater influence of environmental factors acting on a smaller spatial scale, on the occurrence and distribution of dispersive functional categories in the studied tropical estuaries.