Bat diversity in the Waterberg mountain catchment, Limpopo province South Africa : patterns and drivers

Abstract

The Waterberg Mountain Catchment (WMC) in Limpopo, South Africa, is an important region due to its diverse environments. A large area of the WMC was designated as a United Nations Educational, Scientific and Cultural Organization (UNESCO) Biosphere Reserve in 2001. The WMC spans approximately 650000 hectares and includes a variety of vegetation types and geological formations. There have been shifts in land-use within the WMC, with a recent rise in wildlife-based activities, such as eco-tourism, hunting, and wildlife production. While tourism is often seen as beneficial for biodiversity conservation, it can sometimes lead to decreased diversity due to habitat loss from infrastructure development and the introduction of non-native species. Agriculture, including crop production and livestock farming, is a significant influence in the region, affecting local wildlife by reducing potential habitat and resources, which can lead to increased interspecific competition. The adverse effects of land-use changes impact volant and non-volant mammals differently, as the sustained flight capabilities of volant species enable them to overcome barriers between areas with enough resources to sustain them. Bats are categorised into foraging guilds based on their morphology and behavioural traits. These guilds include open-space foragers, edge-space foragers, and clutter-space foragers, each adapted to different environmental conditions. By using these foraging guilds and species richness, I analysed how different land-use types, and other factors of environmental and anthropogenic drivers in the WMC potentially influenced bat diversity and assemblages in the Waterberg. I further investigated how the various factors might affect bat diversity and relative call activity in the WMC to different extents. By analysing bat assemblages in relation to these factors at various scales (30 m, one km and five km), I aimed to provide insights into how these measures at the scales could influence/affect richness and relative call activity. My key question was what species of bat are present in the WMC and what drivers (anthropogenic or natural) might have influenced the presence or absence of various species and the abundances of those species present. I collected data by active capture and release sampling to manually identify bat species with the use of mist nets, harp traps, and by passively recording bat call data using audio recorders. I analysed my processed call data to determine species richness and relative call activity (using Miller’s Index). Generalised linear mixed models were run using variables measured from satellite imagery and QGIS to determine what drivers influenced distribution. I found that bat species richness was relatively homogeneous across the WMC. I recorded 23 bat species, consistent with historical records of 27 species for the region. I recorded two species, Nycticeinops schlieffenii and Neoromicia anchietae, that had not previously been recorded in the area. My results showed that the foraging guilds that contributed the most to species richness were the open-space and edge-space foraging guilds. Aside from foraging guilds, I also grouped species into adapter and avoider species based on roosting habits and how well the species survive in disturbed environments. The relative call activity of adapter species (mainly free-tailed and vesper bats), compared to avoider species (such as horseshoe bats), was higher due to increased anthropogenic disturbances (such as cleared vegetation for buildings, roads, etc.). Cleared vegetation for buildings and roads etc. would result in reduced roosting sites for Rhinolophus species and other clutter-space guild species. Despite similar species richness across properties, species’ relative call activity varied, with edge-space foraging guilds notably predominant. This guild seemed to benefit from low-intensity agriculture, livestock farms, and areas with cleared vegetation. Clutter-space foragers, which are less adaptable and more sensitive to habitat fragmentation, were notably scarce throughout the WMC. Habitat heterogeneity supports species richness by offering diverse resources and roosting sites, but excessive heterogeneity can negatively impact specialized species like clutter-space foragers. While heterogeneity alone does not affect species richness, the availability of space and the degree of fragmentation do. Clutter-space foragers also had lower detection rates due to their higher frequency calls and limited roosting options in southern Africa, leading to increased interspecies competition. Clutter-space forager relative call activity was influenced by the presence of roosting sites and denser vegetation. The generalised linear mixed model results indicated that bat species richness declined with increased normalised difference vegetation index (NDVI) and vegetation complexity, while relative call activity increased with decreased clutter and distance to clutter. Despite the influence of land-use and water availability on bat populations in other studies, I did not detect an influence of these factors on species richness in my study. Small-scale, low-intensity agricultural lands were less impactful than anticipated, possibly due to seasonal activity and water sources being less limiting. Water sources in the Waterberg are more abundant, thus potentially not being limiting as it may have been in other studies. Some studies also show that agricultural properties surrounded by natural vegetation support bat richness and activity. Aside from seasonal influences, my study didn’t include insect abundance (thus food availability) which may have also influenced the results. Elevation and vegetation types were significant at the five km scale, with higher elevations and dense vegetation reducing bat relative call activity and richness. The study concluded that bat richness and relative call activity are influenced by a combination of elevation, NDVI, and distance to clutter, with broader scales (five km) providing clearer insights into distribution patterns. These factors combined would indicate that change in vegetation cover along an elevational gradient could be a driver of diversity. Thus, land-owners and property management should prioritise the maintenance of cluttered habitats to support avoider species, particularly clutter-space foragers. Research into roosting preferences and specific management of vegetation cover could increase prey relative call activity and foraging opportunities for these species. Establishing buffer zones and ecological corridors to reduce habitat fragmentation and maintaining diverse vegetation structures will help support both adapter and avoider species, contributing to the long-term survival of bat populations in the WMC and similar environments.