Beyond the here and now : herbivore ecology in a spatial-temporal context

Ecological phenomena at a certain location often not only depend on the current characteristics of that location itself, but also on characteristics of the landscape surrounding the site or influences from the past. In other words, in order to be able to understand ecological processes here and now, we often need information that is beyond here and now. This thesis investigates the role of such spatial-temporal context on the relationships between species and their environment. The focus is on large mammalian herbivores, an in particular the factors determining the movement and distribution of African elephants (Loxodonta africana) in Kruger National Park (KNP), South Africa. This thesis covers four main themes. First, it is shown that spatial-temporal variation in the biotic and abiotic environment creates predictable seasonal and daily cyclic patterns in the distribution of elephants in KNP. Then, herbivores are shown not only to respond to environmental heterogeneity: they also can create distinct spatial patterning in savanna vegetation when foraging initiates a positive plant-herbivore feedback and when the foraging process is spatially explicit. This leads to specific sites being revisited often, and therefore the patterns of site revisitation by elephants in KNP are studied, mainly in relation to surface water availability and vegetation characteristics. Lastly, this thesis focuses on the scale-dependent response of organisms to environmental heterogeneity, showing the consequences of a mismatch in the scale of analysis on statistical inference, and then focusing on finding the appropriate spatial scales to analyse and predict the spatial distribution of elephants in KNP. Together, the chapters presented in this thesis highlight the importance of explicitly considering the scale and context dependency of species-environment relationships, and demonstrate methods to take issues of spatial-temporal scale and context into account. These methods have the potential to increase our understanding of ecological phenomena and therefore may lead to better management of natural resources. <br/