Yellowstone Predator-Prey


How does the recovery of large predators affect
prey distribution and abundance?

Ecological Background:


The reintroduction of wolves to Yellowstone National Park is often highlighted as one of our greatest conservation experiments.  Following reintroduction in 1995, wolves quickly expanded throughout the park.  At the same time, the elk population decline and some riparian plant communities began to recovery.  Given the rate of plant recovery, and the still abundant elk population, some ecologists suggested that wolves had created a ‘landscape of fear’ in which elk changed their grazing behaviors and spatial distribution leading to a behaviorally-mediated trophic cascade.  Despite this, there is still great uncertainty surrounding the role that wolves have played in both the recovery of riparian plants and the abundance of elk.

Our Study System: 


Yellowstone National Park was established in 1872 as the world’s first national park.  Within the park, we focus our work on the Northern Range elk herd.  This is one of seven herds that uses the park, and is the only herd that maintains a year-round presence.  We focus our efforts here because of year-round access, and because this portion of the park is also the focus of other large-predator research studies on both wolves and cougars.

What We Found:


From 2001-2004, extensive GPS collaring of elk occurred throughout northern range allowing us to examine elk spatial movements in relation to wolf hunting areas, kill sites, and vegetation cover.  We found that elk only avoided wolves for a few hours of the day when wolves were most actively hunting, and as such it is unlikely that this limited spatial response could be responsible for a large-scale change in the vegetation.  Moreover, we found that the large-scale shifts in the distribution of elk from inside the park toward the outside of the park is driven primarily by differences in survival and reproduction between the two segments of the elk population.  As such, there is little evidence that supports the idea of the landscape of fear in Yellowstone.  It is more likely than any subsequent plant response within the park is due to the reduction of elk numbers cause by a full suite of predators including bears, wolves, cougars, and human hunters outside of the park. If you want to hear more, feel free to check out my dissertation talk on YouTube.

Relevant publications:

Metz, M. M., J. SunderRaj, D. W. Smith, D. R. Stahler, M. T. Kohl, K. A. Cassidy, and M. Hebblewhite. [2020]. Accounting for imperfect detection in observational studies: modeling wolf sightability in Yellowstone National Park. Ecosphere 11:e03153.

Wilmers, C., M. C. Metz, D. R. Stahler, M. T. Kohl, C. Geremia, and D. W. Smith. [2020]. How climate impacts the composition of wolf‐killed elk in northern Yellowstone National Park. Journal of Animal Ecology 89:1511-1519.

Cusack, J, M. T. Kohl, M. C. Metz, T. Coulson, D. R. Stahler, D. W. Smith, and D. R. MacNulty. [2020]. Weak spatiotemporal response of prey to predation risk in a freely interacting system. Journal of Animal Ecology 89:120-131.

Kohl, M. T., T. K. Ruth, D. R. Stahler, M. C. Metz, D. W. Smith, and D. R. MacNulty. [2019]. Do prey select for vacant hunting domains to minimize a multi-predator threat? Ecology Letters22:1724-1733.

Kohl, M. T., T. A. Messmer, B. A. Crabb, M. R. Guttery, D. K. Dahlgren, R. T. Larsen, S. N. Frey, S. Liguori, R. J. Baxter. [2019]. The effects of electric power lines on the breeding ecology of greater sage-grouse. PLOS ONE 14(1): e0209968.

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