LTREB Renewal: Mechanisms driving facultative switching in a partially migratory large-herbivore population

Migratory species are crucial to ecosystem function because by migrating they can attain higher abundance, and thus often drive ecological processes. Yet migratory species are also declining worldwide because of human disturbance, habitat loss, and environmental variability. In particular, large ungulates (e.g., deer, elk) are both ecologically and economically important (e.g., hunting), and yet their migrations are also in decline.

Understanding the causes of declining migratory ungulates has important implications for their conservation and management. However, across migratory species, there are usually individuals who migrate and individuals who do not migrate within a single population. Previous research also showed individual ungulates can be flexible in their migratory behavior, deciding whether to migrate or not, or where to migrate, based on changes in their environment.

This research will take advantage of a 19-year, long-term study of migratory elk in a western North American montane landscape to understand both the causes of migratory decision-making in elk, as well as the population consequences of changes in migratory behavior to the management of elk. This research will have broad implications for population and habitat management for a wide range of economically-important migratory ungulate species such as deer and elk across western North America.

This research will extend our long-term 19-year demographic study of a partially migratory elk population on the border of Banff National Park, Alberta, to address the mechanisms driving partial migration. The core data for this research is understanding the demography of over 400 individually marked female elk of known ages, their reproductive rates, and juvenile survival, combined with spatial analyses of their migratory behavior measured by Global Positioning System (GPS) collars.

We will test whether elk switch between migratory strategies in a manner consistent with intrinsic factors (e.g. age, body condition), extrinsic factors (e.g, climate), or density-dependent mechanisms. By monitoring intrinsic factors such as age and reproductive history, as well as extrinsic variation in forage and predation risk, we will test amongst competing and interacting hypotheses to understand why a long-lived mammal switches between migratory strategies in the face of environmental change.

We will then develop a flexible Bayesian integrated population model to test the consequences of migratory switching on population dynamics. This model will be generalizable to other partially migratory species

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.