Freshwater Biodiversity–environment relationships: Quantifying and decomposing the components of beta diversity in tropical stream macroinvertebrates communities

Abstract

There is considerable understanding of biodiversity–environment interactions in terms of species composition and richness, while other categories of biodiversity components, especially beta-diversity, have been scarcely considered and attended to in the tropics, and no attention at all in Nigeria. We examined effects of environmental and spatial factors on beta-diversity in a tropical biodiversity hotspot. We surveyed 15 near-pristine/reference streams for benthic macroinvertebrates in the northern part of Nigeria. Beta-diversity was calculated based on multiple sites of the near-pristine/reference stations combined (15 streams). We examined variation in each component of beta diversity by obtaining dissimilarity matrices based on species abundance data and presence-absence data to quantify the contributions of each component of beta diversity to total beta diversity. We employed variation partitioning approach in decomposing variations in community composition of macroinvertebrates along sets of categorical/predictor variables. Macroinvertebrates communities revealed that analysis involving both abundance and presence-absence were characterized by relative high degree of beta diversity. Turnover component of biodiversity accounted for high levels of total beta diversity, while the effect nestedness component (Simpson) was negligible. Variation partitioning revealed a relatively large pure fractions for environmental variable for Bray-Curtis, total, and turnover components as their pure fraction values were 14 %, 14 %, and 10 % respectively. However, small pure fractions were associated with geographical variables for Bray-Curtis, total, and turnover components with values of 3 %, 4 %, and 3 %, respectively. Similarly, the shared effects of environmental variables and geographical coordinates for Bray-Curtis, total, and turnover components were negligible as they all were associated with 0 % shared effects. No variable was related with nestedness-related community composition. dbRDA plot based on Bray-Curtis and total beta diversity revealed strong variation in species structure was related to environmental conditions. Our finding suggests that while species sorting is an important driver of ecological community in a small spatial scale metacommunity, the spatial factors and processes may also assume significance in structuring variations, but such variations are negligible and could be attributed to co-variance with other unexplained factors.