Abstract
Turnover (i.e., species substitution) and nestedness (i.e., subsets of species from more diverse locations), the two main mechanisms used to explain the beta diversity of biological communities, have different implications for biodiversity conservation. To better understand how these mechanisms contribute to beta diversity, we tested the following hypotheses: (i) greater dissimilarity in community composition occurs between estuarine zones than other hierarchical level studied; (ii) beta diversity in these communities develops by turnover in estuaries with a lower degree of anthropogenic impact, but by nestedness in estuaries with a greater degree of anthropogenic impact; and (iii) the structuring mechanism is independent of season. We studied two tropical estuaries (dry and wet seasons) that vary in terms of land-use of the drainage basins. Subtidal benthic macroinvertebrates were sampled along the estuarine gradient in each of the two estuaries. The additive partitioning approach to species diversity was used to determine the hierarchical scale with the greatest dissimilarity in community composition. General beta diversity was measured using the Sorensen dissimilarity index, partitioning the turnover and nestedness components. The greatest dissimilarity in the composition of the communities occurred between the zones along the estuarine gradient in both seasons (dry = 58.6%; wet = 46.3%). In the estuary with a lower degree of anthropogenic influence, benthic macroinvertebrate diversity was generated by turnover regardless of the season. In the estuary with a greater degree of anthropogenic impact, beta diversity was structured by turnover during the dry season and a combination of both mechanisms during the wet season. We conclude that turnover is the principal mechanism responsible for beta diversity in benthic macroinvertebrate communities in tropical estuaries.
Highlights
Understanding the composition and distribution of biological communities in relation to environmental conditions on a local or regional level is one of the main challenges facing ecologists [1]
A total of 17,407 individuals were recorded in the dry season and 7031 individuals were recorded in the wet season in the two estuaries
The estuarine gradient exerted the greatest influence on dissimilarities in the benthic macroinvertebrate communities analyzed (β3 scale), with greater proportions of variability on the highest hierarchical levels in both seasons, which confirms our first hypothesis
Summary
Understanding the composition and distribution of biological communities in relation to environmental conditions on a local or regional level is one of the main challenges facing ecologists [1]. Partitioning diversity allows a better comprehension of the mechanisms that guide the structuring of communities along environmental gradients and over spatial scales [2]. The total diversity of species in a given region (gamma, γ) is composed of alpha and beta components [3], which can vary along spatial, temporal or environmental gradients [4, 5]. The scientific community has focused his studies on beta diversity using the additive partitioning approach. This approach allows us to understand the spatial scales that generate variations in community composition and affect the formation and evolution of biological communities in different environments [8, 9]. The relative importance of the dissimilarity mechanism varies in accordance with the spatial scale considered and temporal changes [11, 12]
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