Weak relationships among macroinvertebrates beta diversity (β), river status, and environmental correlates in a tropical biodiversity hotspot

Abstract

Freshwater biodiversity is rapidly declining due to accelerated human-induced disturbances. Increased human-induced environmental disturbances are believed not to only decrease species numbers, but to also diminish beta diversity, for instance, by the local extinction of native species and wide-spread introduction of non-native species – a process widely known as biotic homogenization. Here, we investigated whether anthropogenic impacts reduce beta diversity. We also assessed the relative roles of environmental and spatial factors in driving beta diversity. We examined relationships among macroinvertebrates beta diversity, stream status classes (reference and impacted classes), and environmental predictors in streams in Northern Nigeria. We used PERMDISP and distance-based redundancy analysis followed by variation partitioning to evaluate how beta diversity of macroinvertebrates differed between the reference and impacted sites, and what mechanisms were responsible for their responses. While beta diversity between reference and impacted sites was similar for all distance matrices, there were significant differences in composition related to turnover between the reference and impacted sites using the distance matrices. Species sorting prevailed in structuring macroinvertebrates communities in our system, while spatial variables were not relevant. Our result of beta diversity of macro- invertebrates and their responses to disturbances support the hypothesis that disturbances do not necessarily lead to biotic homogenization. We recommend that tropical streams restoration ecologists need to emphasize the study of varying condition classes in their attempt to develop effective restoration strategies based on their environmental heterogeneity.