Spatial distribution of Serengeti wildebeest in relation to resources

We investigated the spatial distribution of radio-marked wildebeest (Connochaetes taurinus) in the Serengeti ecosystem in relation to the distribution of their food resources, comparing patterns in the wet and dry seasons and at local and landscape spatial scales. A mechanistic model of ruminant energy optimization predicted that wildebeest should maximize energy intake on swards 3 cm high and maintain energy balance on swards between 3 and 10 cm high. At the ecosystem scale, wildebeest preferred short and intermediate-height grass of moderate greenness during both the wet and dry seasons. This was consistent with the model prediction which suggests that large-scale movements by wildebeest are motivated, at least partially, by an energy-maximizing strategy. At the local scale, however, wildebeest showed spatial selectivity only on the basis of grass greenness, not on grass height. This differed from model expectations and may have resulted from wildebeest exploiting ephemeral green flushes of grass caused by localized rainfall in their movement radius. According to these results, the influence of other nutritional or behavioural factors on wildebeest distributions is not rejected, yet they suggest the potentially important role of an energy intake maximizing strategy on movement patterns. Our findings show that wildebeest movements are broadly similar to those of other large herbivores that migrate in response to resource gradients.

Predation models for primary and secondary prey species

In Australia, the red fox (Vulpes vulpes) is a generalist predator of European rabbits (Oryctolagus cuniculus) and a range of small to medium-sized native species. The available evidence suggests that foxes are capable of regulating rabbits in semi-arid environments but their role in the population dynamics of other prey species is not clear. A series of models, and associated experimental tests, that compare the effects of predation on primary and secondary prey species are described. The models are appropriate to the time scale of prey dynamics and differ from recent predator–prey models that focus on predator dynamics. These ideas are discussed for the fox and several of its prey species in Australia.