The physiological ecology and thermal biology of the western and eastern pygmy-possums ('Cercartetus' spp.)

Abstract

Much of contemporary knowledge about heterothermy in small mammals has been derived from eutherian species inhabiting seasonally distinct environments in the northern hemisphere. The differences between these species and those living in more unpredictable environments are largely unexplored, leaving gaps in understanding. On the Australian continent, mammals from all three subclasses enter torpor; however studies are limited and most are restricted to laboratory investigations. Of the marsupials, only five species from two families are known to enter prolonged torpor or hibernation (i.e. torpor bouts > 24 h in duration); four pygmy-possums (Burramyidae) and the feathertail glider (Acrobatidae). Nevertheless, this group of marsupials has attracted relatively little attention from ecophysiologists. Therefore, the aim of my thesis was to investigate the physiological ecology, thermal biology and use of torpor in the western pygmy-possum 'Cercartetus concinnus' (13 g) and the eastern pygmy-possum 'C. nanus' (26 g), the two most closely related burramyids. Both species are arboreal, nocturnal and omnivorous/nectarivorous, but inhabit vastly different environments. They are known to enter prolonged torpor in captivity in response to low ambient temperature (Ta), but information about their expression of heterothermy in the wild is restricted to incidental trapping accounts. In this thesis I have combined laboratory studies with work conducted on free-ranging individuals to investigate torpor use, body temperature (Tb), metabolic rate (MR), thermal conductance, ventilation, water economy, activity patterns and habitat use of these species. The comparative analysis of my results has bettered our understanding of how these and other small heterotherms function, survive and persist in their natural habitats.