The role of foraging behaviour in the sexual segregation of the African elephant

Abstract

Elephants (Loxodonta africana) exhibit pronounced sexual dimorphism, and in this study we test the prediction that the differences in body size and sociality are significant enough to drive divergent foraging strategies and ultimately sexual segregation. Body size influences the foraging behaviour of herbivores through the differential scaling coefficients of metabolism and gut size, with larger bodied individuals being able to tolerate greater quantities of low-quality, fibrous vegetation, whilst having lower mass-specific energy requirements. We test two distinct theories: the scramble competition hypothesis (SCH) and the forage selection hypothesis (FSH). Comprehensive behavioural data were collected from the Pongola Game Reserve and the Phinda Private Game Reserve in South Africa over a 2.5-year period. The data were analysed using sex as the independent variable. Adult females targeted a wider range of species, adopted a more selective foraging approach and exhibited greater bite rates as predicted by the body size hypothesis and the increased demands of reproductive investment (lactation and pregnancy). Males had longer feeding bouts, displayed significantly more destructive behaviour (31% of observations, 11% for females) and ingested greater quantities of forage during each feeding bout. The independent ranging behaviour of adult males enables them to have longer foraging bouts as they experience fewer social constraints than females. The SCH was rejected as a cause of sexual segregation due to the relative abundance of low quality forage, and the fact that feeding heights were similar for both males and females. However, we conclude that the differences in the foraging strategies of the sexes are sufficient to cause spatial segregation as postulated by the FSH. Sexual dimorphism and the associated behavioural differences have important implications for the management and conservation of elephant and other dimorphic species, with the sexes effectively acting as distinct "ecological species".

Tree cover and biomass increase in a southern African savanna despite growing elephant population

“…Availability of permanent water allows water-dependent animals to reside in an area throughout the year, leading to a high impact on vegetation in the immediate vicinity of waterpoints (Owen-Smith 2002, Shannon et al 2006, Smit et al 2007a). For example, in Kruger National Park (0.63 elephants/km2; Blanc et al 2007) tree density is close to zero in the first 100 m, and subsequently increases up to a distance of 2.8 km from AWPs (Thrash 1998, Brits et al 2002.…”

“…While calf-caring herds roam within close proximity to permanent water, bulls are known to cover much larger distances. Indeed, independently ranging elephant bulls have been readily observed to browse at distances >10 km from water (Stokke and du Toit 2002, Shannon et al 2006, Chamaille´-Jammes et al 2007. Also the feeding behavior of elephant bulls differs from that of cows, whereby bulls are more destructive, targeting taller trees, while cows show a preference for smaller trees (Styles and Skinner 1997, Shannon et al 2008.…”

Genetic evidence for spatial structuring in a continuous African elephant (Loxodonta africana) population

“…We hypothesised that (i) there would be high mtDNA and nDNA gene flow across the entire region due to the lack of dispersal barriers, and (ii) the patterns of structuring implied by mtDNA and nDNA will differ as a consequence of gender differences in spatial use (Stokke and du Toit 2002;Shannon et al 2006) and social behaviour (e.g. Archie et al 2006Archie et al , 2008 of male and female elephants.…”

Stable isotope turnover and variability in tail hairs of captive and free-ranging African elephants (Loxodonta africana) reveal dietary niche differences within populations

“…For instance, the degree of seasonal switching is not constant across populations; niche breadths appear to become limited in habitats with low browse species diversity, or where high grass biomass is maintained year-round (Jachmann and Bell 1985;Owen-Smith 1988;Codron et al 2006aCodron et al , 2006bCodron et al , 2011b. Intrinsic constraints, primarily changes in nutritional requirements and accessibility of resources across body size classes, also influence levels of dietary variability, especially for large taxa like elephants in which size varies considerably with age and (or) is strongly dimorphic across the sexes (Shannon et al 2006;Woolley et al 2011). In many animal populations, diets also differ between individuals of the same age or sex class (Bolnick et al 2003(Bolnick et al , 2007, and although such individual niche segregation throughout the entire seasonal cycle is unlikely for mammal herbivores (Codron et al 2012), the phenomenon nevertheless presents a potential source of variability contributing to the dietary niche breadths of whole populations.…”