Seasonal Variation in Thermoregulatory Behavior and Body Temperature of Diurnal Kalahari Lizards

Abstract

We discuss seasonal variation in thermoregulatory behavior and its consequences on body temperature for 12 species of diurnal lizards in the southern Kalahari semidesert of Africa and also evaluate several methods of attempting to document thermoregulatory behavior using a descriptive data base. Lizards vary time of activity among seasons, which limits the variation in ambient conditions actually experienced. Ground—dwelling lizards and probably arboreal lizards move nonrandomly with respect to sun and shade; thus the percentage of lizards in sun in inversely proportional to air temperature. Arboreal lizards shift to higher perches at midday in summer and to logs or ground in winter thus decreasing and increasing incident heat loads, respectively. Both juveniles and adults of 3 species, only juveniles of 2 species, and only adults in 1 species are active in winter: both adults and juveniles of 6 species brumate [= hibernate]. Mean body temperature (T b ) varies within days and among months and is positively correlated with corresponding mean air temperature (T a ) in almost all species. Nonetheless, correlation and regression analysis suggests that thermoregulatory behaviors reduce the impact of variations in ambient conditions on Kalahari lizards. The mean T b of different species reflect evolutionary relationships. In summer, mean T b is proportional to the percentage of lizards in sun and with the tendency of lizards to be active only in summer. Thus, lizards with inferred low optimal temperatures are active during more months of the year.