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Optimal predator management for mountain sheep conservation depends on the strength of mesopredator release

Prugh, Laura R., Arthur, Stephen M.
Oikos 2015 v.124 no.9 pp. 1241-1250
Canis latrans, Canis lupus, Ovis dalli, adults, case studies, ewes, fecundity, lambs, models, population growth, predation, predators, survival rate, wolves, Alaska
Large predators often suppress ungulate population growth, but they may also suppress the abundance of smaller predators that prey on neonatal ungulates. Antagonistic interactions among predators may therefore need to be integrated into predator–prey models to effectively manage ungulate–predator systems. We present a modeling framework that examines the net impact of interacting predators on the population growth rate of shared prey, using interactions among wolves Canis lupus, coyotes Canis latrans and Dall sheep Ovis dalli dalli as a case study. Wolf control is currently employed on approximately 16 million ha in Alaska to increase the abundance of ungulates for human harvest. We hypothesized that the positive effects of wolf control on Dall sheep population growth could be counteracted by increased levels of predation by coyotes. Coyotes and Dall sheep adult females (ewes) and lambs were radiocollared in the Alaska Range from 1999–2005 to estimate fecundity, age‐specific survival rates, and causes of mortality in an area without wolf control. We used stage‐structured population models to simulate the net effect of wolf control on Dall sheep population growth (λ). Our models accounted for stage‐specific predation rates by wolves and coyotes, compensatory mortality, and the potential release of coyote populations due to wolf control. Wolves were the main predators of ewes, coyotes were the main predators of lambs, and wolves were the main source of mortality for coyotes. Population models predicted that wolf control could increase sheep λ by 4% per year in the absence of mesopredator release. However, if wolf control released coyote populations, our models predicted that sheep λ could decrease by up to 3% per year. These results highlight the importance of integrating antagonistic interactions among predators into predator–prey models, because the net effect of predator management on shared prey can depend critically on the strength of mesopredator release.