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Refuge characteristics and preferences of Psammobates oculifer in semi-arid savanna

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image of Amphibia-Reptilia

The availability of suitable refuges to buffer temperature extremes may be a critical determinant in the distribution of arid-zone ectotherms. We studied refuge selection of Kalahari tent tortoises over five seasons in two vegetation types to assess how seasonal climate change, vegetation type, and the size difference between sexes influence refuge selection. Plant refuges accounted for 78% and mammal burrows for 22% of refuges used. Burrow use did not differ between vegetation types or sexes but its use increased exponentially with maximum temperature, indicating that mammal burrows may be an essential resource to protect small-bodied tortoises against summer heat. Kalahari tent tortoises preferred grass refuges to other growth forms, whether shrubs or grasses were dominant in the habitat. Tall grass was selected in excess of availability, by males and females in both vegetation types, probably because it was denser than short grass and provided better protection against heat and predators. The increased use of short grass refuges in colder months may be linked to thermal needs because this growth form allowed P. oculifer to bask in filtered sunlight whilst being in cover. Females made greater use than males did of short grass refuges, perhaps because their larger size necessitated longer exposure to sunlight. Body size differences also explain why males required wider and denser refuges than females did to protect them against environmental hazards. Our results underscore the complexities of refuge selection by an arid-zone ectotherm and the role it may play in their distribution.

Affiliations: 1: Chelonian Biodiversity and Conservation, Department of Biodiversity and Conservation Biology, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa


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