Amphibian and reptile communities and functional groups over a land-use gradient in a coastal tropical forest landscape of high richness and endemicity

Abstract

Information on the response of herpetofauna to different land uses is limited though important for land-use planning to support conservation in human-modified landscapes. Though transformation is dogmatically associated with extinction, species respond idiosyncratically to land-use change, and persistence of species in habitat fragments may depend on careful management of the human-modified matrix. We sampled herpetofauna over a vegetation-type gradient representative of regional land uses (old-growth forest, degraded forest, acacia woodland (i.e. new-growth forest), eucalyptus plantation, and sugar cane cultivation) in the forest belt skirting the southeastern coast of Africa, part of a biodiversity hotspot hosting many endemic herpetofaunal species in a highly transformed landscape. We categorized species into trait-derived functional groups, and assessed abundance and richness of groups and compared community metrics along the gradient. We further assessed the capacity of environmental variables to predict richness and abundance. Overall, old-growth forest harbored the highest richness and abundance, and frogs and reptiles responded similarly to the gradient. Richness was low in cultivation and, surprisingly, in degraded forest but substantial in acacia woodland and plantation. Composition differed between natural vegetation types (forest, degraded forest) and anthropogenic types (plantation, cultivation), while acacia woodland grouped with the latter for frogs and the former for reptiles. Functional group richness eroded along the gradient, a pattern driven by sensitivity of fossorial/ground-dependent frogs (F2) and reptiles (R2) and vegetationdwelling frogs (F4) to habitat change. Variables describing temperature, cover, and soil were good predictors of frog abundance, particularly of functional groups, but not for reptiles. Conserving forest and preventing degradation is important for forest herpetofaunal conservation, restoration and plantations have intermediate value, and cultivation is least beneficial. Our study demonstrates the utility of function-related assessments, beyond traditional metrics alone, for understanding community responses to transformation. Particularly, fossorial/ground-dependent frogs and reptiles and vegetation-dwelling frogs should be closely monitored.