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University of Newcastle upon Tyne (2007)

Evolutionary ecology of giraffes (Giraffa camelopardalis) in Etosha National Park, Namibia

Brand, Rachel

Titre : Evolutionary ecology of giraffes (Giraffa camelopardalis) in Etosha National Park, Namibia

Auteur : Brand, Rachel.

Université de soutenance : University of Newcastle upon Tyne

Grade : Doctor of Philosophy (Ph.D.) : 2007

Résumé
The giraffe (Giraffa camelopardalis) occupies a variety of habitats across sub- Saharan Africa. It is characterised by a loose social organisation, and a dominancedriven polygynous mating system. This project sought to explain biogeographic and inter-sexual variation in pelage colouration in the context of natural and sexual selection. I also sought to test the hypothesis that in a semi-arid environment, limited resources (food and water) would predictably concentrate females, increasing the potential for dominant males to monopolise matings. I analysed photos from across Africa, and reveal that where yearly bright sunshine is greater, female giraffe in particular tend to be lighter, resulting in sexual dichromatism in high insolarity locations. I hypothesised that dark pelage colour is maintained in males through sexual selection for a costly status signal. Field work was carried out in Etosha NP, Namibia. Using photographic records, I identified 431 individual giraffe. I surveyed the study area regularly and collected data on group composition and behaviour upon locating giraffe. I carried out focal watches, and recorded all observations of agonistic and mating behaviour. Darker males tended to be older and more dominant than lighter males, associated less with females, but had greater success in courting females. Food and water affected female movements on both a spatial and temporal scale. At waterholes, encounter rates were increased and consequently mating and agonistic interactions more frequent. Paler males had a greater chance of interacting with females at waterholes because of higher intruder pressure, but when present, darker males always monopolised courtship opportunities. Mature males demonstrated a diversity of ranging strategies that affected association with females. These individual differences are assumed to relate to status and probably affect individual reproductive success. Evidence suggests male reproductive success is skewed towards mature dark males, but may also vary among dark males, with some potentially being excluded from mating.

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