Plasticity in physiological condition of female brown bears across diverse ecosystems
Variation in life history strategies facilitates the near global distribution of mammals by expanding realized niche width. We investigated physiological plasticity in the spring body composition of adult female brown bears (Ursus arctos) across 4 diverse Alaskan ecosystems. Brown bears are a highly intelligent omnivore with a historic range spanning much of North America, Europe, and Asia. We hypothesized that body mass, fat mass, lean mass, and total caloric content would increase across populations with increasing food resource availability. Throughout their range, brown bears enter a period of torpor during winter months, decreasing their metabolic rate as an adaptation to this period of reduced food availability. They also give birth to and nourish offspring during this time. Due to this specific life history strategy, we further hypothesized that proportional body fat and the proportion of total calories derived from fat would be consistent across populations. Our results supported our first hypothesis: body, fat, and lean masses, and caloric content of bears across populations increased with the quality and abundance of available food. However, the proportional body fat content and proportion of calories from fat differed across populations indicating population-specific strategies to meet the demands of reduced seasonal food availability, offspring production and rearing, and climate as well as some plasticity to respond to environmental change or ecosystem perturbations. Investigations of body condition and energetics benefit from combined assessments of absolute, proportional, and caloric metrics to understand the nuances of brown bear physiological dynamics across and within populations.
KeywordsBody composition Brown bear Energy Plasticity Ursus arctos
We thank biologists W. Deacy and A. Morehouse, wildlife veterinarian J. Powers, and pilots A. Greenblatt, M. Keller, J. DeCreeft, R. Richotte, C. Cebulski, D. Welty, I. Bedingfield, K. Rees, K. VanHatten, and J. and J. Cummings for their assistance with animal capture and handling. N. Svoboda and three anonymous reviewers provided insightful comments and improved the manuscript. Funding was provided by the National Park Service, U.S. Fish and Wildlife Service, and U.S. Geological Survey. All procedures performed in studies involving animals were in accordance with the ethical standards of the institutions or practice at which the studies were conducted. Use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U. S. Government.
- Bergmann C (1847) Über die verhältnisse der wärmeökonomie der thiere zu ihrer grösse. Göttinger Studien 3:595–708Google Scholar
- Hilderbrand GV (2017) Brown bear spring energetics, Alaska 2014–2016. U.S. Geological Survey data release. https://doi.org/10.5066/F7CZ35ND
- Hilderbrand GV, Gustine DD, Mangipane B, Joly K, Leacock W, Mangipane L, Erlenbach J, Sorum MS, Cameron MD, Belant JL, Cambier T (in press). Body size and lean mass of brown bears across and withing four diverse ecosystems. J ZoolGoogle Scholar
- Holm S (1979) A simple sequentially rejective multiple test procedure. Scand J Stat 6:65–70Google Scholar
- Monahan W B, Rosemartin A, Gerst K L, Fisichelli N A, Ault T, Schwartz M D, Gross J E, Weltzin J F (2016) Climate change is advancing spring onset across the U.S. National park system. Ecosphere 7(10):45. https://doi.org/10.1002/ecs2.1465
- Pasitschniak-Arts M (1993) Mammalian Species: Ursus arctos. The Amer Soc Mammal 493:1–10Google Scholar
- Robbins CT (2001) Wildlife Feeding and Nutrition. Academic Press, San DiegoGoogle Scholar
- Schwartz CC, Haroldson MA, White GC (2006) Survival of cub and yearling grizzly bears in the greater Yellowstone ecosystem, 1983–2002. Wildl Monographs 161:18–24Google Scholar
- Servheen C. 1999. Bear status survey and conservation action plan. IUCNGoogle Scholar
- Sidak Z (1967) Rectangular confidence region for the means of multivariate normal distributions. J Amer Stat Assoc 62:626–633Google Scholar
- Suring LH, Del Frate G (2002) Spatial analyses of locations of brown bears killed in defense of life or property on the Kenai Peninsula, Alaska, USA. Ursus 13:237–245Google Scholar
- Zar JH (1999) Biostatistical analysis, 4th edn. Prentice Hall, Inc., New JerseyGoogle Scholar