Conservation implications of food webs involving wolves, coyotes, and pronghorn

Coyote (Canis latrans) predation is an important factor in the mortality of neonatal pronghorn (Antilocapra americana). It has been suggested that the extirpation of gray wolves (Canis lupus ) contributed to an overall increase in coyote densities and a concomitant rise in predation rates on pronghorn fawns, a process known as trophic cascades. To test this hypothesis we contrasted cause-specific mortality and survival rates of fawns captured at wolf-free and wolf-abundant sites; used demographic modeling to assess the impact of wolves on pronghorn population dynamics; and evaluated coyote survival rates, causes-specific mortality, and spatial segregation with wolves, to identify mechanisms by which wolves limit coyote densities. Fawn survival rates were 400% higher, and coyote densities 33% lower, at sites used by wolves. Wolves killed 56% of transient coyotes, and dispersal rates of transients were 117% higher at the wolf-abundant site; thus, differential effects on solitary coyotes may be an important mechanism by which wolves reduce coyote densities. Our results support the hypothesis that the extirpation of wolves contributes to high rates of coyote predation on pronghorn fawns, and add to a growing body of evidence demonstrating the importance of top-down forces in structuring the dynamics of consumer-resource interactions.