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

in Amphibia-Reptilia
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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.

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

in Amphibia-Reptilia



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    (a) Monthly rainfall at the study site and at Kimberley airport, ca. 5 km from the study site, and the long-term rainfall average (± SD; 46 years, 1960-2005) at Kimberley airport. (b) Mean monthly maxima and minima temperatures (± SD) for the study period at Kimberley airport.

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    Mean (± SD) monthly refuge widths (a) and heights (b). No data were collected in June 2006 and data of the first and last days of November were added to October and December, respectively.

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    Seasonal use of refuge types by Psammobates oculifer in combined sites. Refuge types include mammal burrows (black bars), short grass (hatched bars), tall grass (grey bars), short shrubs (white bars) and remaining refuge types (horizontal bars) which had small occurrences (unknown grass, herbs, tall shrubs and trees).

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