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ABSTRACT: Knowledge of density‐dependent responses in grizzly bears is largely circumstantial yet critical to managing populations near carrying capacity. We studied grizzly bear (Ursus arctos) body condition and demographics in Denali National Park, Alaska, USA, 1991–1998, and compared our results with data from a nearby heavily hunted population to better understand the characteristics of a naturally regulated bear population. We captured grizzly bears just after den emergence in spring (May) and just before den entrance in fall (Sep). We measured body fat using bioelectrical impedance analysis, estimated bear ages, and fitted adult, subadult, and 2‐year‐old dependent bears with telemetry‐collars. We used capture‐mark‐resight techniques to estimate density. We estimated grizzly bear density at 37 bears/1,000 km2; density of adult and subadult bears was 27 bears/1,000 km2. Adult females that produced cubs had 40% more fat and 10% more lean mass pre‐denning than non‐reproductive females but had similar lean mass and similar but very low body fat (8%) post‐denning. Adult females that produced cubs lost more fat and lean mass over winter than non‐reproductive adult females. The physiological demand on adult females producing cubs was 29 kg of total body mass split evenly between fat mass and lean mass. Females that did not lose cubs during the cubs’ first summer averaged more body fat the previous fall than those that lost partial or entire litters. Reproductive rate (0.34) and average litter size (2.1) were high and comparable to increasing populations (λ > 0). Age of dependent young at family breakup (2.9 yr) and age of first reproduction (7.5 yr) were high and comparable to declining populations (λ < 0). Cub (0.34), cub litter (0.43), and yearling survival rates (0.46) were low. Subadult and adult survival rates were high (0.94–1.00) for both sexes. The female age structure was bimodal, suggesting episodic recruitment. The percentage of subadult males was low (3% of population and 10% of male segment). We conclude that the grizzly bear population in Denali National Park was near or at carrying capacity relative to available nutritional resources, adult female access to nutritional resources determined whether cubs were born and the likelihood of their survival, and high dependent bear mortality was the primary factor limiting recruitment and regulating the population. © 2018 The Wildlife Society. [ABSTRACT FROM AUTHOR]

This is a Forum article in response to: Barber‐Meyer, S. (2015) Trophic cascades from wolves to grizzly bears or changing abundance of bears and alternate foods? Journal of Animal Ecology, 83, doi: 10.1111/1365‐2656.12338. We used multiple data sets and study areas as well as several lines of evidence to investigate potential trophic linkages in Yellowstone National Park. Our results suggest that a trophic cascade from wolves to elk to berry production to berry consumption by grizzly bears may now be underway in the Park. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate changes in expression of known cellular regulators of metabolism during hyperphagia (Sept) and hibernation (Jan) in skeletal muscle and adipose tissue of brown bears and determine whether signaling molecules and transcription factors known to respond to changes in cellular energy state are involved in the regulation of these metabolic adaptations. During hibernation, serum levels of cortisol, glycerol, and triglycerides were elevated, and protein expression and activation of AMPK in skeletal muscle and adipose tissue were reduced. mRNA expression of the co-activator PGC-1α was reduced in all tissues in hibernation whereas mRNA expression of the transcription factor PPAR-α was reduced in the vastus lateralis muscle and adipose tissue only. During hibernation, gene expression of ATGL and CD36 was not altered; however, HSL gene expression was reduced in adipose tissue. During hibernation gene expression of the lipogenic enzyme DGAT in all tissues and the expression of the FA oxidative enzyme LCAD in the vastus lateralis muscle were reduced. Gene and protein expression of the glucose transporter GLUT4 was decreased in adipose tissue in hibernation. Our data suggest that high cortisol levels are a key adaptation during hibernation and link cortisol to a reduced activation of the AMPK/PGC-1α/PPAR-α axis in the regulation of metabolism in skeletal muscle and adipose tissue. Moreover, our results indicate that during this phase of hibernation at a time when metabolic rate is significantly reduced metabolic adaptations in peripheral tissues seek to limit the detrimental effects of unduly large energy dissipation. Unlabelled Image • Cellular mechanisms underlying tissue-specific changes in metabolism during hibernation have yet to be completely defined. • During hibernation cortisol appears linked to activation of the AMPK/PGC-1α/PPAR-α axis in skeletal muscle and adipose tissue. • Adaptations in peripheral tissues favor lipid metabolism and limit detrimental effects of unduly large energy dissipation [ABSTRACT FROM AUTHOR]