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Foraging competition, vigilance and group size in two species of gregarious antelope

Lookup NU author(s): Dr Henrik Lange


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In gregarious species, rates of foraging behaviour are often positively related to group size while there is simultsneously a negative relation between group size and vigilance. Although the mechanisms underlying these behavioural patterns are still incompletely understood, decreased predation risk or increased foraging competition in larger groups have been put forward as two possible explanations. Since most empirical tests of these two hypotheses have used manipulative experiments, they have mainly been limited to small-bodied species or to animals in captivity. Here we suggest a time-budget model to test for the causal effects of predation risk and foraging competition that does not necessitate manipulative approaches. We used this method on two species of gregarious antelope, blesbok (Damaliscus pygargus phillipsi) and impala (Aepyceros melampus). We suggest that increased foraging competition In large groups drives the negative relationship between vigilance and group size in these species. This study shows that observational data can be used to test explicit hypotheses on species that are logistically unsuitable for manipulative experiments, and also render support for hypotheses suggesting that factors unrelated to predation risk are involved in shaping the differences in vigilance rates over different group sizes in gregarious species.

Publication metadata

Author(s): Dalerum F, Lange H, Skarpe C, Rooke T, Inga B, Bateman PW

Publication type: Article

Publication status: Published

Journal: South African Journal of Wildlife Research

Year: 2008

Volume: 38

Issue: 2

Pages: 138-145

Print publication date: 01/10/2008

ISSN (print): 0379-4369

ISSN (electronic): 1996-8477

Publisher: South African Bureau for Scientific Publications


DOI: 10.3957/0379-4369-38.2.138


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