Factors driving range expansion of white-tailed deer, Odocoileus virginianus, in the boreal forest of northern Alberta, Canada

A large suite of species, across numerous taxa, are expanding their geographic ranges, with potential impacts on species, communities and ecosystems. This has increased interest in understanding the mechanisms driving range change and anticipating future changes in species’ distributions. White-tailed deer have expanded their range into the boreal forest in North America. For northern ungulates, energy expenditure for thermoregulation and movement in winter can exceed energy gain from limited resources, leading to mortality. Substantial changes in climate and land use over the last half of the 20th century may have decreased winter energy loss or increased resource abundance, facilitating range expansion. The objective for this dissertation was to determine the relative importance of climate change and land use as drivers of white-tailed deer range expansion in northern Alberta and to predict how the range may change during the first half of the 21st century. I developed a method to calculate a winter severity index for white-tailed deer using widely available data, and used this mechanistically relevant metric of winter climate in a species distribution model analysis. White-tailed deer presence in the 2000s was explained by a positive relationship with land use footprint, deciduous forest, and growing season length and a negative relationship with winter severity and wetland. The only important land use footprints were agriculture, forestry, and well pads. Model predictions for the northern Alberta boreal region had relatively good accuracy, according to assessments with independent data from the 1970s, 1980s, 1990s, and 2000s decades. Climate was found to be the most important factor driving range expansion in this region. If the shifts toward less severe winters and longer growing seasons continue at the rate observed, white-tailed deer will be able to occupy the majority of the northern Alberta boreal by the 2050s. This increases concern for northern caribou populations and suggests wildlife managers in Alberta face big challenges now and into the future.