Morley, Kate
(2016)
Shifting correlates of lizard thermal biology through space: the effect of climate and habitat on lizard body temperatures.
MRes thesis, University of Nottingham.
Abstract
With climate warming, many lizard species are at risk of extinction. This is largely due to low dispersal abilities, which may prevent range shifts to more thermally suitable environments, and due to low capacities of species to physiologically adapt to warmer temperatures. Therefore, understanding relationships between body temperatures and environmental variables, and how they vary with habitat, is key to understanding the relative vulnerability of species to climate change.
Here I use regression to examine relationships between lizard body temperatures and environmental variables, including environmental temperature, temperature seasonality, precipitation, precipitation seasonality, potential evapotranspiration, leaf area index (LAI) and land surface temperature, at a global scale. These variables have been linked in local scale studies to lizard thermal biology. However, little research has been done to examine broadscale trends, or how environmental variables interact to influence body temperature. I then evaluate whether relationships vary with land cover (closed, semi-open and open vegetation, urban, and barren), preferred substrate (arboreal, saxicolous, psammophilous, ground, fossorial and semi-aquatic), activity time (nocturnal, diurnal) and insularity (island, mainland). Again, habitat effects on body temperature are yet to be considered beyond local scales.
Results show that accounting for habitat in global models significantly improves model fit. The global model explained 33.7% of the variation in body temperature, rising to 70.0% for closed vegetation and barren environments, and 82.1% for urban environments. The relationships between environmental variables and body temperature, and the relative contribution of variables to explaining body temperature, vary with land cover, substrate and insularity, suggesting that species within different habitats will face different threats as climate changes. For example, reduced canopy covers expected with climate change may increase the rate of warming for tropical forest species, indicative through negative correlations between LAI and body temperature amongst closed vegetation. In barren environments, increasing drought frequency and intensity may be the greatest threats, suggested through the strong influence of temperature seasonality and precipitation in the barren model. For diurnal species, LAI was the strongest contributor to body temperature, however LAI was absent from the nocturnal species model. This supports that the effect of LAI on body temperature is related to shade availability, and suggests that LAI data can be used to capture the effects of shade availability on operative temperatures. Although previous studies have noted the importance of shade for thermoregulation, no attempts have been made to incorporate remotely sensed data such as LAI as a measure of shade availability.
Incorporating climate and habitat data into models, including LAI, will allow for improved predictions of lizard body temperatures at global scales. Extending models to include future climates and shade levels under different land cover and climate change scenarios may therefore provide more accurate predictions about which species and habitats are most vulnerable to climate change.
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