Limits to the distribution of the southern African Ice Rat (<i>Otomys sloggetti</i>): thermal physiology or competitive exclusion?

Abstract

1. We test the hypothesis that the thermal physiology of Otomys sloggetti restricts its distribution to altitudes above 2000 m, below which it does not occur. 2. The thermal physiology of O . sloggetti is typical of rodents from warm/hot areas: the thermoneutral zone is relatively broad and lies between 26 and 28 °C; the upper limit of the thermoneutral zone can be extended by 4 °C through the use of hyperthermia; basal metabolic rate concurs with the allometrically predicted value; the lower critical temperature is high; minimal thermal conductance is 21% higher than the allometrically predicted value; and the capacity for noradrenaline‐induced non‐shivering thermogenesis is 19% lower than the allometrically predicted value. 3. Evaporative water loss and water flux rates are high and typical of mesic‐adapted rodents. 4. The absence of O . sloggetti from warmer, lower‐lying habitats cannot be attributed to its thermal physiology. We suggest that non‐physiological factors, such as interspecific competition with Otomys irroratus , are more likely to restrict the distribution of O . sloggetti .