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my research
thesis
how and why does the importance of temperature in setting species’ range limits vary?
Species are already shifting their range limits in response to climate warming, resulting in the global redistribution of biodiversity. Yet variation in the sensitivity of species ranges to warming indicates that the importance of temperature in restricting ranges varies, both between species and across the different edges of a range. The little empirical evidence investigated to date suggests that general patterns exist; temperature appears more important in restricting marine versus terrestrial ranges, and at the cold versus warm edge of a species' range. And where temperature is less important, other factors like dispersal limitation, biotic interactions, and other environmental tolerances are thought to be implicated in restricting the range.
My thesis brings together existing data to empirically assess how and why the relationship between temperature and range limits differs interspecifically (between species) and geographically (across the edges of a species’ range). I am conducting a global study on how ectotherm species (reptiles, amphibians, insects, and fish) fill their thermal niches using potential thermal ranges, or the geographic shapes that enclose all habitats with temperatures that populations of a species could theoretically survive in. I will soon test hypotheses about what explains these patterns, asking whether there is evidence that when ranges are less strongly limited by temperature, they are more strongly limited by dispersal, biotic interactions, or other tolerances.
ongoing work
does dispersal limitation explain variation in species range shifts?
Although dispersal limitation is recognized as a important factor that might cause species range shifts to lag behind the climate expectation, dispersal traits to date have explained little variation in observed range shifts. However, previous studies have often confounded the role of dispersal by combining data on both range expansions and contractions, and have used proximate dispersal traits that limit our capacity to compare them directly to climate velocity.
Considering only range expansion fronts and using dispersal distances (in meters), I am working closely alongside members of the BIOSHIFTS project to test the hypothesis that dispersal is limiting to range shifts only when the species’ maximum annual dispersal distance is lower than the annual distance of climate velocity. This work was begun during my Research Stay at the Centre for Synthesis and Analysis of Biodiversity in Montpellier, France, and was supported by an NSERC Michael Smith Foreign Study Supplement.
global patterns of change in the autocorrelation of temperature
The autocorrelation of temperature is changing globally as a result of anthropogenic climate change. Analyses show that on average the power spectrum of temperature is ‘reddening’, meaning that autocorrelation is increasing and that bouts of extreme temperatures are becoming more likely to persist for longer (Di Cecco & Gouhier, 2018). Theory predicts that spectral reddening of environmental variables may increase population extinction risk by way of external forcing (Steele, 1985; Inchausti & Halley, 2001), however, we lack empirical evidence of this. Additionally, spatial variation in spectral change remans unexplored.
As part of the Life In Fluctuating Environments CIEE Working Group, I am undertaking a Research Assistantship to investigate spatial patterns of spectral change and explore its ecological consequences.
drivers of intraspecific variation in thermal tolerance
Collaborators: Joey Bernhardt, Juan Rubalcaba, Jennifer Sunday
Being able to accurately predict species-level responses to anthropogenic climate change is a major challenge facing biologists of the current decade. Although many projections have been made about species’ responses to climate warming based on their physiological thermal limits, these studies often ignore the sometimes high amount of variation in thermal physiology observed across a species’ range, that is driven either by phenotypic variation or genetic differences between populations.
During my BSc degree, I worked with collaborators and used species traits to investigate whether there is evidence that:
1. the amount of thermal variation a population experiences drives the evolution of phenotypic plasticity in thermal tolerance
2. local adaptation accounts for intraspecific variation.in thermal traits
thermal risk and population decline
Collaborators: Joey Bernhardt, Juan Rubalcaba, Ilona Naujokaitis-Lewis, Jennifer Sunday
Thermal tolerance limits, representing the temperature at which the performance of an individual organism measured in a lab declines to zero, are often used to represent the temperature at which a population of a species experiences detrimental effects. However, we lack empirical evidence that when individual organisms experience temperatures exceeding their thermal limits, the effect scales up to the population level. Using existing data on the thermal tolerance, traits, and population trends of hundreds of ectotherm species, we are investigating the link between thermal safety and population decline to fill this knowledge gap.
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