Current Zoology(formerly Acta Zoologica Sinica), Aug. 2008, 54(4): 561 - 568
The influence of sexual dimorphism on the foraging behaviour of the nyala Tragelaphus angasii (In English)
Taryn KIRBY, Graeme SHANNON, Bruce PAGE, Rob SLOTOW
S c h o o l o f B i o l o g i c a l a n d C o n s e r v a t i o n S c i e n c e s , U n i v e r s i t y o f K w a Z u l u - N a t a l , W e s t v i l l e C a m p u s , U n i v e r s i t y o f K w a Z u l u - N a t a l , P r i v a t e B a g X 5 4 0 0 1 , D u r b a n 4 0 0 0 , S o u t h A f r i c a
Sexual dimorphism is pronounced in nyala Tragelaphus angasii and is predicted to have a significant influence on their foraging behaviour and habitat selection due to the allometric relationships associated with increasing body size. A continuous behavioural sampling method was used to detect male and female differences in habitat and plant utilisation. Food species were recorded and feeding heights compared between the sexes. Vegetation surveys were conducted once a feeding bout had ended using the point centred quarter (PCQ) technique. A Discriminant Function Analysis was then used to identify whether species and height class preferences were significantly different between the sexes. Female nyala spent a similar proportion of time foraging in all three habitats, whilst males exhibited a preference for sand forest. The differences within habitats were even more marked, with males selecting a greater proportion of woody species and feeding at a greater average height, whilst females preferred to forage lower down in the herbaceous layer. Male and female nyala appear to exhibit dietary and spatial segregation within habitats at the plant and patch scale. We suggest that this is a result of different nutritional and energetic demands which are driven by body size dimorphism and divergent reproductive strategies. Ultimately browsers may exhibit spatial segregeation within woody habitats due to the increased spatial heterogeneity that is generated by their complex structure [Acta Zoologica Sinica 54(4):561 –568, 2008].