Get access

INDIRECT EFFECTS AND TRADITIONAL TROPHIC CASCADES: A TEST INVOLVING WOLVES, COYOTES, AND PRONGHORN

Authors

  • Kim Murray Berger,

    1. Department of Wildland Resources, Utah State University, Logan, Utah 84322-5230 USA
    2. Wildlife Conservation Society, Northern Rockies Field Office, 205 Natural Science Building, University of Montana, Missoula, Montana 59812 USA
    Search for more papers by this author
    •  Address for correspondence: Wildlife Conservation Society, Northern Rockies Field Office, 205 Natural Science Building, University of Montana, Missoula, Montana 59812 USA. E-mail: kberger@wcs.org

  • Eric M. Gese,

    1. United States Department of Agriculture, Wildlife Services, National Wildlife Research Center, Department of Wildland Resources, Utah State University, Logan, Utah 84322-5230 USA
    Search for more papers by this author
  • Joel Berger

    1. Wildlife Conservation Society, Northern Rockies Field Office, 205 Natural Science Building, University of Montana, Missoula, Montana 59812 USA
    Search for more papers by this author

  • Corresponding Editor: J. M. Fryxell.

Abstract

The traditional trophic cascades model is based on consumer–resource interactions at each link in a food chain. However, trophic-level interactions, such as mesocarnivore release resulting from intraguild predation, may also be important mediators of cascades. From September 2001 to August 2004, we used spatial and seasonal heterogeneity in wolf distribution and abundance in the southern Greater Yellowstone Ecosystem to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus), accounts for high rates of coyote predation on pronghorn (Antilocapra americana) fawns observed in some areas. Results of this ecological perturbation in wolf densities, coyote densities, and pronghorn neonatal survival at wolf-free and wolf-abundant sites support the existence of a species-level trophic cascade. That wolves precipitated a trophic cascade was evidenced by fawn survival rates that were four-fold higher at sites used by wolves. A negative correlation between coyote and wolf densities supports the hypothesis that interspecific interactions between the two species facilitated the difference in fawn survival. Whereas densities of resident coyotes were similar between wolf-free and wolf-abundant sites, the abundance of transient coyotes was significantly lower in areas used by wolves. Thus, differential effects of wolves on solitary coyotes may be an important mechanism by which wolves limit coyote densities. Our results support the hypothesis that mesopredator release of coyotes contributes to high rates of coyote predation on pronghorn fawns, and demonstrate the importance of alternative food web pathways in structuring the dynamics of terrestrial systems.

Ancillary