Can snow skinks survive climate change? : The potential for behaviour, physiology and competition to mitigate and enhance climate change impacts on snow skink life history, distribution and persistence
Creators: name: Caldwell, AJ
Publisher: name: University Of Tasmania
Year: 2023

description: Shifting climates are affecting a diverse range of species, with many taxa predicted to become extinct. A great proportion of reptile species are at risk of extinction within the 21st century due to climate change, yet species-specific impacts of climate change are difficult to predict. This is partly due to inter-specific variance in the physiological and behavioural traits which mediate environmental temperature effects at the organismal level. A Tasmanian lizard genus, Niveoscincus, provides an excellent example of this, as variation in altitudinal distribution between species has led to divergent adaptations to local thermal conditions. In this thesis, I provide a systematic assessment of traits likely to mediate climate change effects on widespread lowland and range-restricted highland members of the Niveoscincus genus. Variation in thermal niche width underlies extinction risk from climate change, yet basal physiological data is often unavailable and there is little understanding of the way physiology varies within and between species. I determined the critical thermal limits and evaporative water loss rates of a widespread lowland species of snow skink, N. metallicus, and two highland species of snow skink, N. microlepidotus and N. greeni, in a laboratory setting. I found that the widespread lowland species had significantly higher critical thermal minimum and maximum temperatures, and significantly lower evaporative water loss rates than either of the highland species. I then examined the potential for these critical thermal limits to mediate climate effects on the activity periods from 2010 ‚Äö- 2100. Projections indicate that both widespread lowland and highland snow skink species will experience an increase in their available activity period during the 21st century under predicted climate change. Behavioural plasticity is at the forefront of organisms' potential to respond to novel environments yet our understanding of the extent of behavioural plasticity possessed by species is limited. I examined the potential for behavioural responses to changes in basking opportunity by a high and low altitude population of two widespread lowland species, N. ocellatus and N. metallicus, and two highland species of snow skink, N. microlepidotus and N. greeni, in a laboratory setting. All of the populations and species showed reductions in the time spent basking in response to increased basking opportunity. The widespread lowland species, but not the highland species, showed reductions in body temperature when exposed to increased basking opportunity. These plastic behavioural and body temperature responses to the thermal environment have the potential to mediate climate change effects on these species. Annually reproducing widespread lowland Niveoscincus species interact with biennially reproducing highland Niveoscincus species in narrow zones ~1100 m above sea level. Warming temperatures projected under climate change may enable widespread lowland species to invade higher altitude areas. Consequently, the reduced reproductive rate of highland species may act as an evolutionary trap under climate change, as widespread lowland species outnumber and outcompete highland species at increasingly high altitude areas. Using a spatially-explicit individual-based model I simulated an interacting population of the widespread lowland, N. ocellatus, and the highland, N. microlepidotus, snow skink species on Mount Wellington, Tasmania. Higher temperatures were projected to increase the abundance and upper range boundary of N. ocellatus. The increase in competition for territory is predicted to drive N. microlepidotus into a long acting extinction vortex. Intra- and inter-specific differences in behaviour, physiology and phenology, along with climate-mediated variation in life history traits, are likely to impact the responses of species to climate change. However, the majority of species distribution models do not explicitly incorporate these factors, potentially resulting in erroneous predictions. I incorporated a wide range of biological trait data into a process-based model, NicheMapR, to test the effects of projected climate change on the life history, activity and distribution of N. ocellatus and N. microlepidotus. These models predicted climate change would result in a number of fitness benefits for both of these species, including increased reproductive output and frequency. When simulated across an altitudinal transect the models predicted the widespread lowland species would be able to colonise higher altitude sites under projected climate change. This thesis represents a comparative examination of the potential for climate change to impact the life history, persistence and distribution of several reptile species. My results suggest that climate change impacts are likely to be population and species-specific, according to climatic and biological processes operating at local scales. This study highlights the potential for climate change to have a number of beneficial effects on the fitness of temperate reptile taxa. However, the downstream effects of climate change for species' abundance, range margins and long term persistence depend on climatic effects on, and responses of, neighbouring competitors. My findings support the call for studies of climate change impacts to take a process-based approach and suggest metamodels provide a promising avenue for future research into the prediction of the responses of species to climate.