The effects of sexual dimorphism on the movements and foraging ecology of the African elephant.

Abstract

Large herbivores are key components of terrestrial biomes because of their relative abundance and pronounced influence on ecosystem functioning and habitat structure. To manage and conserve these species effectively, requires greater understanding of their distribution and use of resources at varying spatial and temporal scales. Sexual dimorphism is one aspect of large herbivore ecology likely to have a significant effect on resource use and community level interactions. Elephants present an ideal species to test the influence of sexual dimorphism due to their marked body size and pronounced behavioural differences. This study used location and behavioural data collected over an 8 year period in five different South African reserves, all of which had well documented elephant populations. The reserves were relatively small (<1000 km2) and had augmented water supplies so analyses were not influenced by surface water availability. Results indicated that male and female elephants resolve their available range at distinctly different scales. Both sexes were shown to expand their ranges with increasing forage quality, however males were the most flexible in their temporal and spatial response during periods of low resource availability. Females were more selective than males, targeting higher quality forage and being less destructive in their feeding approach. This may be due to females' higher mass specific energy requirements associated with their smaller body size and substantial reproductive investment. They were also constrained by the costs of group living compared to male elephants which range independently. Sexual segregation is a consequence of body size dimorphism and was investigated at both the habitat and plant scale to elucidate the mechanism driving the separation of the sexes. Whilst individual habitat preferences exist, these are not sufficient to segregate the sexes. At the plant scale, significant differences were shown with regard to foraging duration, tree size and plant parts eaten. Further investigation of sexual segregation involved testing the recently proposed activity budget hypothesis. Males and females have similar daily activity budgets and relatively high levels of behavioural synchrony, which is not sufficient to explain segregation. Instead, the marked sexual segregation appeared to be caused by social organisation, reproductive strategies and the divergent foraging behaviour of males and females at the plant scale. This research highlights the importance of considering male and female dimorphic herbivores as ecologically distinct species. For example, male elephants are likely to be driving the majority of destructive foraging bouts and this will often be in a heterogeneous manner, especially during periods of resource scarcity. Therefore, the effective management of elephants requires considering population structure, individual behaviour and population size.