Abstract
Lizards in Aotearoa are a diverse assemblage of two almost entirely endemic lineages, however over 85% of these species are currently classified as at-risk or threatened due to habitat loss and introduced predators. Rapid anthropogenic climate breakdown in the 21st century is predicted to push threatened species closer towards extinction. Lizards are considered to be particularly at risk from climate change due to their limited capacity to disperse out of climatically unsuitable habitats. Globally 20% of lizard species are predicted to become extinct as increasing temperatures force them to remain inactive in thermal refugia. In this thesis I studied the thermal ecology of cold-adapted, heliothermic (sun-basking) skinks in sub-alpine habitat in Otago, to assess how they might respond to climate change. To determine the upper thermal limits of activity I measured the critical thermal maximum and voluntary thermal maximum of McCann’s skink (Oligosoma maccanni). I then developed a method to miniaturise commercially available temperature loggers so that they could be attached to skinks as small as 3 g and used as a thermal bio-logger. This allowed me record semi-continuous skin temperatures for McCann’s skink and the larger, endangered Otago skink (O. otagense) in situ. This revealed that both species are able to thermoregulate to maintain body temperatures when the maximum operative temperatures of their habitat exceed their voluntary thermal maximum. This behaviour allows maintenance of skin temperatures below the skink’s thermal limits, possibly through shuttling between thermally disparate microclimates (assumed to be exposed rock surfaces and thermal refugia in rock crevices). The thermal bio-loggers were also used in a laboratory experiment where I confirmed under controlled conditions that McCann’s skink thermoregulates using a dual set-point mode of thermoregulation when offered a range of operative temperatures and established the upper and lower set-point temperatures that the skinks thermoregulated between. I then compared thermoregulation between experimental treatments where skinks could only elevate their body temperatures by exposing themselves to wind. Exposure to wind significantly reduced the temperature of both upper and lower set-points even while operative temperatures remained fixed. Collectively the results of these studies suggest that heliothermic Oligosoma species will be able to maintain activity even under the most pessimistic climate change projections. However, it remains to be determined whether other ecologically important activities other than thermoregulation are restricted at times when the operative temperatures of exposed habitats exceed skinks’ thermal limits.