Ontogenteic alteration of activity and habitat selection by Bufo marinus

Abstract

Recently metamorphosed Bufo marinus exhibit patterns of activity and habitat use that vary in relation to changes in weather and moisture availability. Activity adjacent to water is greatest on moist substrates at high daytime temperatures in windy weather. Conditions that inhibit evaporative cooling (no wind, dry substrates, high humidity), or are likely to lead to low body temperatures (cool temperatures at night under windy conditions) restrict activity. Activity in habitats away from permanent water is dependent on metamorphlings having grown large enough to allow night-time activity on dry substrates. Growth leads to a change in activity from diurnal as metarnorphlings, to nocturnal and diurnal as juveniles (30-70 mm SVL), and to nocturnal as adulthood approaches. Size-dependent changes in patterns of activity and habitat use are accompanied by changes in pelvic patch morphology and body pigmentation. The morphological changes may have resulted from selection acting to minimise time spent in the smaller size classes which are vulnerable to predators, competitors and the environment, and size-dependent optimisation of chemical defences.