Assessing Signals of Mesopredator Release under Two Apex Predator Regimes in Tswalu Kalahari Reserve, South Africa

Abstract

Predators have a considerable influence on the structure and functioning of the ecosystems in which they occur, however their numbers have declined, and continue to do so. The eradication of top-level predators has been shown to cause cascading effects on the dynamics of surrounding biological assemblages. Mesopredator Release (MR) is one of these effects. The mesopredator release hypothesis posits that in the absence of apex predators, mesopredators respond functionally by increasing their populations. The Tswalu Kalahari Reserve (TKR) provides a unique opportunity to test this hypothesis in the context of an arid savanna that is managed according to conservation principles and that supports a diversity of indigenous species. The TKR is composed of two component regions, Korannaberg and Lekgaba, separated by predator-proof fencing, under two different predator management regimes. At the time of my study Korannaberg supported wild dogs (Lycaon pictus, Temminck, 1820) and cheetah (Acinonyx jubatus, Schreber, 1775) as top predators (no lions), and Lekgaba supported lions (Panthera leo, Linnaeus, 1758) (no wild dogs or cheetah). For the purpose of my study, I considered both sections homogenous. Both areas support similar assemblages of mesopredators, and a variety of species that are considered prey for mesopredators. I used a quantitative field experiment to gather numerical and empirical data. In this comparative study, I selected sample sites within Korannaberg and Lekgaba using a randomisation process. I compared large predator, mesopredator, large and small ungulate, small mammal and avian relative abundance and diversity, between regions and among seasons. I assessed the relative abundance and diversity of mesopredators and ungulates using camera traps, small mammals using live-trapping transects and birds using modified point counts. I detected no significant differences in relative abundances of the mesopredators (p > 0.05), ungulates (p > 0.05), small mammals (p > 0.05), or birds (p > 0.05), between the two sections, nor differences in diversity either. My results support an increasing body of knowledge suggesting that mesopredator release may not be a ubiquitous phenomenon. Previous studies have evaluated evidence (or lack thereof) for the mesopredator relase hypothesis in the African and more specifically South African context, however, none have been conducted in the Kalahari. In the Eastern Cape of South Africa, mesopredator release was demonstrated through a higher relative abundance of black-backed jackals (Lupulella mesomelas (Schreber, 1775) in the absence of apex predators, however in the Karoo, the control of top predators did not have an effect on the rate of predation of ground-dwelling bird nests. I did, however, find substantial seasonal differences in abundance and diversity of small mammals, with a higher number of captures in the cold-dry season. Additionally, avian populations had a higher relative abundance in the cold-dry season, and a higher diversity in the hot-wet season. There were no seasonal differences in relative abundance or diversity of predators or ungulates (large or small).