Comparative effects of urban and agricultural land transformation on Odonata assemblages in a biodiversity hotspot

Abstract

Rivers of the Cape Floristic Region (CFR) biodiversity hotspot are threatened by land transformation. This region is a centre of endemism for many taxa, including Odonata. These insects are highly sensitive to changes in physical habitat structure, which makes them good bioindicators, and this led to the development of the Dragonfly Biotic Index (DBI). We investigated the effects of local agricultural and urban land transformations on Odonata species richness, assemblage composition and DBI scores in three CFR rivers. A total of 48 sites were selected and categorized as natural, agricultural or urban land use. Adult male Odonata and four environmental variables were recorded over two seasons. Land transformation significantly influenced Odonata assemblage composition but did not always significantly reduce species richness. Average vegetation height also affected Odonata assemblage composition and decreased species richness. Agricultural and urban sites had Odonata assemblages differing from those in the natural areas. Agricultural and urban local land use types reduced opportunities for some endemic species but provided for the persistence and establishment of widespread, generalist species, as indicated by great changes in DBI scores. Mitigating the adverse influences of land transformation through establishment of protected areas is essential for the conservation of rare taxa, particularly in an area with a high number of endemic species.