Prey risk allocation in a grazing ecosystem.

Area of Science:

• Ecology
• Behavioral Ecology
• Wildlife Management

Background:

• Understanding predator-prey interactions is crucial for ecosystem dynamics, particularly indirect effects mediated by prey behavior.
• Quantifying how predators influence ungulate group size and distribution, alongside other factors, is needed in predator-ungulate-plant systems.
• The risk allocation hypothesis suggests prey behavior adapts to predation risk based on exposure frequency.

Purpose of the Study:

• To identify non-predation variables influencing elk (Cervus elaphus) group size and distribution on winter ranges.
• To evaluate the risk allocation hypothesis regarding elk responses to wolf (Canis lupus) predation risk.
• To assess how wolf predation risk affects elk distribution and subsequent impacts on plant communities.

Main Methods:

• Conducted surveys across 513 1-km2 areas over two years in the Greater Yellowstone Ecosystem (GYE).
• Utilized logistic and log-linear regression to analyze elk group size and distribution data.
• Employed model selection to test the risk allocation hypothesis against other a priori hypotheses, controlling for non-wolf predation variables.

Main Results:

• Wolf presence showed little effect on elk group sizes, which were primarily influenced by habitat type and human hunting.
• Elk exhibited more dynamic distribution patterns in areas frequently patrolled by wolves, aligning with the risk allocation hypothesis.
• Wolf-induced shifts in elk distribution are predicted to dilute foraging pressure and reduce spatial heterogeneity of impacts on grasslands.

Conclusions:

• Habitat and human hunting are stronger drivers of elk group size than wolf predation.
• Wolves indirectly influence plant communities by altering elk distribution and foraging patterns in frequently hunted zones.
• Findings support the risk allocation hypothesis and suggest wolves can mitigate localized overgrazing in the GYE.