Land use changes in an afrotropical biodiversity hotspot affect stream alpha and beta diversity

Abstract

Land use changes such as deforestation and agricultural expansion strongly affect stream biodiversity, with several studies demonstrating negative impacts on stream alpha diversity. Effects of forest conversion on stream beta diversity are much harder to predict, both because empirical studies are few and because competing theories suggest opposite responses. Moreover, almost no data exist for tropical Africa, a region that is paradoxically a hotspot of both current deforestation and freshwater biodiversity. Here, we compared environmental variables, invertebrate community composition, and alpha and beta diversity of forested and deforested (agricultural) streams in and around Kibale National Park, Uganda. We found that forest conversion strongly influenced stream environmental variables and invertebrate community composition, and that agricultural land use reduced stream alpha diversity. However, among-stream beta diversity was greater across the agricultural landscape than inside the forest. Decomposing beta diversity into taxa replacement and richness differences demonstrated that replacement contributed a similar proportion to total beta diversity in both land use classes. Because of this greater beta diversity, the agricultural landscape had similar gamma diversity as the forested landscape despite its lower alpha diversity. We discuss conservation implications of these land use-associated biodiversity changes in a highly diverse yet little-studied deforestation hotspot.