Density dependence, whitebark pine, and vital rates of grizzly bears

• Published in: The Journal of Wildlife Management
• Main Authors: van Manen, Frank T., Haroldson, Mark A., Bjornlie, Daniel D., Ebinger, Michael R., Thompson, Daniel J., Costello, Cecily M., White, Gary C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2015
• Subjects: Ursus arctos
• Online Access: http://dx.doi.org/10.1002/jwmg.1005; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjwmg.1005; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jwmg.1005; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/jwmg.1005

ABSTRACT Understanding factors influencing changes in population trajectory is important for effective wildlife management, particularly for populations of conservation concern. Annual population growth of the grizzly bear ( Ursus arctos ) population in the Greater Yellowstone Ecosystem, USA has slowed from 4.2–7.6% during 1983–2001 to 0.3–2.2% during 2002–2011. Substantial changes in availability of a key food source and bear population density have occurred. Whitebark pine ( Pinus albicaulis ), the seeds of which are a valuable but variable fall food for grizzly bears, has experienced substantial mortality primarily due to a mountain pine beetle ( Dendroctonus ponderosae ) outbreak that started in the early 2000s. Positive growth rates of grizzly bears have resulted in populations reaching high densities in some areas and have contributed to continued range expansion. We tested research hypotheses to examine if changes in vital rates detected during the past decade were more associated with whitebark pine decline or, alternatively, increasing grizzly bear density. We focused our assessment on known‐fate data to estimate survival of cubs‐of‐the‐year (cubs), yearlings, and independent bears (≥2 yrs), and reproductive transition of females from having no offspring to having cubs. We used spatially and temporally explicit indices for grizzly bear density and whitebark pine mortality as individual covariates. Models indicated moderate support for an increase in survival of independent male bears over 1983–2012, whereas independent female survival did not change. Cub survival, yearling survival, and reproductive transition from no offspring to cubs all changed during the 30‐year study period, with lower rates evident during the last 10–15 years. Cub survival and reproductive transition were negatively associated with an index of grizzly bear density, indicating greater declines where bear densities were higher. Our analyses did not support a similar relationship for the index of whitebark pine mortality. The results ...