Ecosystem consequences of re-established and recovering populations of large carnivores remain uncertain, especially with regards to the direct and indirect effects of competition with subordinate carnivores. Given that large carnivores have the potential to disproportionally effect species interactions and biomass structure in food webs and initiate trophic cascades more frequently than smaller carnivores, ecosystem consequences are, however, likely significant. New interspecific competition scenarios following the recovery of large carnivores may also interact with established management strategies, including hunting, thus magnifying potential negative impacts on subordinate carnivores. Our objective was to test whether the dual impacts of hunting and competition with re-established wolves (Canis lupus) resulted in reduced survivorship and population declines in subordinate pumas (Puma concolor) in the Southern Yellowstone Ecosystem, USA. To achieve our objective, we used data from 14 years of puma monitoring concurrent with the re-colonization of the area by wolves to estimate survival, and age- and cause-specific mortality rates. We then developed matrix models to estimate population growth and employed sensitivity and elasticity analyses to quantify the relative contributions of cause-specific mortality rates attributable to hunting and wolf recovery.
Results/Conclusions
Our results showed that survival of pumas was strongly age-specific and varied between seasons for residents (kittens = 0.27 ±0.05 and 0.50 ±0.07; juveniles = 0.71 ±0.04 and 0.86 ±0.03; resident adults = 0.81 ±0.02 and 0.91 ±0.02). In addition, dispersing individuals experienced significantly lower annual survival probabilities than residents. With emigrants censored, survival models accounting for the impact of hunting consistently outperformed all other candidate models, though recovering wolves contributed to reduced survival of pumas. Results from our matrix models suggested that the resident puma population declined (λ = 0.80 ± 0.04 when accounting for emigration; λ = 0.97 ± 0.04 excluding emigration), and that a moratorium on hunting would be required for puma populations to be stable. Predicted puma population declines were confirmed by observations in the field. Our results highlight the complexity of communities with multiple predators and competitors, including humans, and some direct and indirect effects of manipulating or changing the abundance of a dominant carnivore. The magnitude of changes in puma and wolf densities we observed over our 14-year study period, however, was unexpected, and illustrated a human-facilitated shift from a predator-prey system dominated by a solitary felid to one dominated by a social canid.