Spatially explicit carrying capacity estimates to inform species specific recovery objectives: Grizzly bear (Ursus arctos) recovery in the North Cascades

Abstract

The worldwide decline of large carnivores is concerning, particularly given the important roles they play in shaping ecosystems and conserving biodiversity. Estimating the capacity of an ecosystem to support a large carnivore population is essential for establishing reasonable and quantifiable recovery goals, determining how population recovery may rely on connectivity, and determining the feasibility of investing limited public resources toward recovery. We present a case study that synthesized advances in habitat selection and spatially-explicit individual-based population modeling, while integrating habitat data, human activities, demographic parameters and complex life histories to estimate grizzly bear carrying capacity in the North Cascades Ecosystem in Washington. Because access management plays such a critical role in wildlife conservation, we also quantified road influence on carrying capacity. Carrying capacity estimatesranged from 83 to 402 female grizzly bears. As expected, larger home ranges resulted in smaller populations and roads decreased habitat effectiveness by over 30%. Because carrying capacity was estimated with a static habitat map, the output is best interpreted as an index of habitat carrying capacity under current conditions. The mid-range scenario results of 139 females, or a total population of 278 bears, represented the most plausible scenario for this ecosystem. Grizzly bear distribution generally corresponded to areas with higher quality habitat and less road influence near the central region of the ecosystem. Our results reaffirm the North Cascades Ecosystem's capacity to support a robust grizzly bear population. Our approach, however, can assist managers anywhere ecosystem-specific information is limited. This approach may be useful to land and wildlife managers as they consider grizzly bear population recovery objectives and make important decisions relative to the conservation of wildlife populations worldwide.