Basking in the Australian water dragon Physignathus lesueurii; why do alpha males not respond to operative temperatures in the same way as adults and sub-adults?

Abstract

AbstractObservations have been made on the behaviour of the Australian water dragon Physignathus lesueurii in southeast Australia. Physical models that explore the thermal environment at a similar spatial level as real lizards were related to ontogenetic changes in lizard behaviour. Current theory predicts that a heliotherm will bask in open locations to optimise heating rates in order to attain target body temperatures as quickly as possible. Movement to shaded or partially shaded areas then maintains thermal stability. Regression equations of basking intensity in relation to operative temperatures were employed to test this theory. The behaviour of adults, which were not alpha males, and sub adults was in agreement with the prediction, but the behaviour of alpha males was not: the regression coefficient did not differ significantly from 0. In general, sub adult lizards were more active and fed more often than larger lizards although this relationship changed with different times of the day. The results suggest differing costs for thermoregulation for different size classes, particularly in alpha males where territory defence has a key role.