Institute of Evolutionary Biology and Environmental Studies, University of Zurich, 8006 Zürich, SWITZERLAND.
This work investigated patterns of habitat use and segregation among species of the large African carnivore guild: the African wild dog, the spotted hyena and the lion. In particular, I studied what role temporal and spatial partitioning of activities, respectively, use of space may play in promoting coexistence. The study site was the Okavango Delta in northern Botswana, one of the few remaining places in Africa where the three species still co-occur in a pristine and undisturbed ecosystem.
In Chapter Two we investigated the degree of temporal segregation between the allegedly diurnal wild dogs and the nocturnal spotted hyenas and lions. Wild dogs are commonly described as day active, and such behaviour has been described as an adaptation to evade interactions with the two other dominant species. We, however, showed a degree of temporal overlap considerably higher than previously described. Such overlap was mainly due to the unexpected nocturnal behaviour of wild dogs that was mainly influenced by moonlight availability, rather than by the activity of hyenas and lions. Our results thus raise some questions concerning the real role of spotted hyenas and lions in shaping the activity patterns of wild dogs and highlight how temporal overlap may only play a marginal role in enhancing coexistence among the species.
Chapter Three demonstrated that the spatial distribution of wild dogs was negatively influenced by the distribution of lions, but not by that of spotted hyenas. In areas catheterized by a low lion presence, wild dogs may take advantage of the best resources, but they were restricted in their behaviour or even excluded from particular areas above a certain lion density, and this irrespectively of other variables such as habitat type and prey availability. Our results highlighted spatial segregation as a key mechanism promoting coexistence between wild dogs and lions. Considering the dramatic rate at which habitat loss and fragmentation are happening, the need for space that allows species coexistence should sound like a warning bell.
In Chapter Four we investigated how the species are affected by and adapt to anthropogenic habitat modification and human activities near the boundary of a protected area. Specifically, we analysed how different types of barrier influenced the distribution and spatial interaction among species and discussed their effects at the community composition level. We showed that lions were restricted in their movements by an artificial fence erected to control the movement of ungulate species, while the other carnivore species freely crossed it. In contrast, lions were not obstructed in their movements by rivers, which represented an almost completely impassable barrier for the smaller spotted hyenas and wild dogs. Reinforcing the findings of Chapter Three, Chapter Four provided further evidence that wild dogs may take advantage of areas characterized by a low lion presence, particularly for critical activities such as raising offspring.
Chapter Five presents density estimates for spotted hyenas and lions in the study area. An accurate estimate was necessary because the intensity of interaction between competing species partly depends on the density at which each species occurs. We calculated a density of 15.4 adult hyenas /100 km2 and 16.2 lions /100 km2. These figures compared well with other highly productive ecosystems of southern and eastern Africa. The hyena and lion density in the Okavango Delta should therefore be considered to be between medium and high.