Evolution of Elevational Range Shifts

As temperatures continue rising globally, many species have begun shifting their distribution upslope and/or poleward. However, species are responding in idiosyncratic ways, and species across their geographic ranges don’t always shift in the same direction. I am interested in the following: 1) What are the extrinsic factors, and associated physiological mechanisms, that underlie elevational range shifts? 2) Why do some species shift while others do not? 3) Do average conditions, or climatic extremes, determine limits? and 4) Why does a species shift in certain areas but not others? Currently, I am working on identifying the drivers of warm-edge (i.e. lower elevation) retractions of American pikas (Ochotona princeps) at their range core here in North America. Managers will be able to use the results of this work to understand the greater extent of elevational shifts across the region, identify areas of greatest future extirpation risk, and apply this information in conservation planning for this species and others.

American pika (Ochotona princeps)

Documented ~800m upslope retractions (red up to green) of pikas across three watersheds in Idaho

Abundance Modelling for Forecasting Distributional Shifts

Population abundances (and densities) are believed to be, in part, representative of habitat quality, which influence vital rates. Abundances have been documented to decline after habitat quality deteriorates, frequently in a lagged manner. Therefore, declining or overall low abundances may act as an early indicator of extinction risk at the population level. Since abundances can be readily measured for most terrestrial species, and robust statistical analyses can be conducted on this continuous variable, I am interested in questions related to this population metric, including, 1) What determines whether species’ exhibits abundance distributions that follow unimodal, bimodal, constant, etc. distributions along abiotic gradients? 2) Do species ‘lean’ upslope and/or northwards prior to shifting their distributions? and 3) Do abundances generally increase before plummeting, influenced by underlying changes in vital rates as a form of demographic compensation, or do they more so decline slowly?

Pronghorn near the Gravelly Range, Montana

Space-for-Time Substitutions and Species-Climate Relationships

Documenting changes in occupancy along biophysical gradients (e.g. elevation) can be a great way to quantify the effects of climate change on species. One approach using these gradients is called a space-for-time substitution. Space-for-time substitutions represent one way we can understand how species might respond to future warming when historical data are lacking. This study design not only allows us to understand where the species’ climatic niche space is currently, but also where it used to be and where it will be in the future. Montane regions are the perfect systems to use such approaches because gradients can be nested; for example, you can survey along elevational gradients in multiple mountain ranges that span a climatic gradient of their own. Since robust historical sampling efforts are rare for most species and regions, I am interested in developing this method further to better understand the strengths and weaknesses it possesses for answering questions in global change research.

Eighteenmile Peak, MT & ID Border