The Limpopo River Exerts a Powerful but Spatially Limited Effect on Bat Communities in a Semi-Arid Region of South Africa

Abstract

Although the Limpopo River is not perennial in its upper stretches in South Africa, the presence of a narrow riparian forest zone is expected to enhance bat diversity by promoting a wider range of foraging types, but the scale at which this effect may operate is not known. A recent, fine-scale model of bat diversity in Africa suggested that rivers may enhance species richness of bats, but that strong gradients in richness would occur next to rivers especially in savanna areas. We tested this idea by conducting acoustic surveys with bat detectors around six water bodies at distances from 0–12 km from the Limpopo River in two adjacent protected areas, the Mapungubwe National Park and the Venetia Limpopo Nature Reserve. We used a paired design, with each water body having detectors placed at and just away (500–750 m) from it. We found enhanced species richness, diversity and activity at MNP sites closer to the Limpopo (0–5 km) compared with VNR sites located 9–12 km from the Limpopo. Moreover, at VNR but not MNP, the bat community was dominated (32% of calls) by an arid-adapted generalist species, the Cape serotine (Neoromica capensis). Consistent with the proximity of structurally complex riparian vegetation, slow flying, clutter-feeding horseshoe bats (Rhinolophus spp.) were relatively more abundant (12% of calls) at MNP compared with VNR (0.7% of calls). This effect was highly accentuated when correcting for detectability of different species to bat detectors. Proximity to small, natural and artificial water bodies significantly enhanced both species richness and activity, but this effect was much more pronounced at sites > 5 km from the Limpopo compared with sites < 2 km from the Limpopo. We conclude that while major rivers with riparian zones can exert a significant impact on species richness, diversity, activity and community structure of insectivorous bats, this effect may only extend a few kilometres from the river. Protection of riparian zones along rivers in savannas is therefore critical to conserving intact and diverse bat communities.