Bats and the Loss of Tree Canopy in African Woodlands

Abstract

We studied the activity patterns, abundance, diversity, and diets of bats, along with the abundance of nocturnal volant insects, at 30 sites in Miombo woodland in northern Zimbabwe. The woodland at 50% of the sites had been disturbed by high elephant densities to the extent that the tree canopy was greatly reduced. The tree canopy was intact at the other sites. Intact and impacted sites differed significantly in tree ( Ͼ 3 m tall; Ͼ 15 cm basal diameter) and shrub (1-3 m tall; Ͻ 1 m tall) diversity and cover. At each site we used ultraviolet lights to sample insects and mist nets and bat detectors to sample bats. To assess their diets we collected and analyzed feces from captured bats. We caught 343 bats representing the families Pteropodidae (1 species), Vespertilionidae (11 species), and Molossidae (3 species). The molossids and vespertilionids are all aerial feeders taking airborne insects. Bat species richness, abundance, and activity were greater at intact than at impacted sites, but these differences were statistically significant only at adjacent sites ( Ͻ 5 km apart) not at more distant intact and impacted sites ( Ͼ 20 km apart). At the adjacent sites we caught a significantly greater proportion of small ( Ͻ 10 g) bats at intact than at impacted sites. These data and a significantly greater proportion of Scotophilus species ( Ͼ 10 g) caught during the early evening at intact than at impacted sites suggested that the removal of canopy trees affected roost availability for the bats. Although larger species may have commuted between intact and impacted sites, smaller species did not. In contrast, the availability of prey did not appear to have been significantly affected by the removal of the canopy trees, as indicated by the light-trap catches of insects and the bats' diets. Most bats ate mainly beetles and moths, the most abundant insects sampled at the ultraviolet lights. Our findings suggest that aerial-feeding bats such as vespertilionids and molossids do not appear to be useful indicators of disturbance in this habitat, even in the face of significant loss of tree canopy. Muriélagos y la Pérdida del Dosel de Arboles en Bosques AfricanosResumen: Estudiamos los patrones de actividad, abundancia, diversidad y dietas de murciélagos, al igual que la abundancia de insectos voladores nocturnos en 30 sitios en el bosque de Miombo al norte de Zimbabwe. El bosque ha sido impactado en un 50% de los sitios por densidades altas de elefantes, a tal grado que el dosel de los árboles ha sido reducido grandemente. El dosel estuvo intacto en los otros sitios. Sitios intactos e impactados difieren significantivamente en diversidad y cobertura de árboles ( Ͼ 3m de altura; Ͼ 15 cm de diámetro basal) y arbustos (1-3 m de altura; Ͻ 1m de altura). En cada sitio usamos luz ultravioleta para muestrear insectos y redes y detectores de murciélagos para muestrear murciélagos. Para determinar sus dietas, colectamos y analizamos heces de los murciélagos capturados. Capturamos 343 murciélagos repre- ‡ ‡ email bfenton@circus.yorku.ca ...

Large-scale impacts of herbivores on the structural diversity of African savannas

“…These differences in turn affect the diversity and richness of animal species, as well as the ecological functioning of these systems. Greater canopy structural diversity enhances the habitat available for a wide range of organisms beyond the herbivore communities (2,3,37,42) and alters such ecological processes as nutrient cycling, seed dispersal, and germination (2,4,43,44). Our findings highlight the trade-offs that managers must grapple with when attempting to sustain biodiversity among plant and various faunal communities.…”

“…T he 3-dimensional (3-D) structure of vegetation is central to the functioning of African savannas, providing habitat for a wide variety of plants and animals (1)(2)(3)(4). Like many regions of the world, African savannas are under increasing pressure from humans, and thus increased emphasis is being placed on natural protected areas to preserve biological diversity (5,6).…”

Vegetation structure influences the vertical stratification of open- and edge-space aerial-foraging bats in harvested forests

“…This contrasts with the distinct peaks often found in other studies (O'Shea and Vaughan, 1977;Anthony et al, 1981;Taylor and O'Neill, 1988;Hayes, 1997). A marked evening activity peak, followed by low activity, has been suggested to indicate the movement of bats away from their roosts to distant foraging areas (Thomas, 1988;Fenton et al, 1998;Grindal and Brigham, 1999). However, vertical stratification studies indicate that bats may simply shift to different heights in the forest to access insect resources or track their changing abundance (Taylor and O'Neill, 1988;Kalcounis et al, 1999;Hayes and Gruver, 2000).…”

Elevated elephant density does not improve ecotourism opportunities: convergence in social and ecological objectives

“…This suggests that tourist numbers in protected areas are more sensitive to extrinsic factors, such as political and economic events, than to the density of elephants. Between 1994 and1998, tourism Studies have found that the high elephant numbers in the AENP have led to changes in habitat structure, which have reduced the richness and abundance of a variety of mammal species (Novellie et al 1996, Fenton et al 1998, Kerley and Landman 2006, Kerley et al 2008. Tourists are attracted to high species diversity (Okello and Yerian 2009), which suggests that stocking animals at high densities to increase ecotourism may present a paradox as it may ultimately lead to a decrease in ecotourism attractions, as also suggested by (Lindsey et al 2007).…”

“…In the subtropical thicket of South Africa, high elephant densities cause a reduction in plant biomass (Pentzhorn et al 1974, Barrett andHall-Martin 1991) and the loss of a range of plant species, including a number of endemic or near-endemic succulents and geophytes (Moolman and Cowling 1994, Lombard et al 2001, Kerley and Landman 2006. It has also been postulated that changes in habitat structure brought about by high elephant numbers in the AENP and elsewhere have reduced the richness and abundance of a variety of animal species (Novellie et al 1996, Fenton et al 1998, Kerley and Landman 2006, Kerley et al 2008. Maintaining species diversity is not only the core objective of protected areas but also this diversity plays an important role in attracting tourists to protected areas (Okello and Yerian 2009).…”