Abstract
Chronic stress and poor body condition can cause adverse physiological and behavioural responses and may make animals more vulnerable to predation. We examined hair cortisol concentration (HCC) and marrow lipid content, as bioindicators of chronic stress and body condition, respectively, of bison (Bison bison bison), moose (Alces alces) and white-tailed deer (Odocoileus virginianus) killed by wolves (Canis lupus) in Prince Albert National Park (PANP), Saskatchewan, Canada. The Sturgeon River plains bison population in PANP is one of only a few wild populations of plains bison in their historical range in Canada and has experienced a decline of around 50% since 2005. We expected wolf-killed bison to have elevated HCC compared to human-harvested bison and that there would be a negative relationship between HCC and marrow lipids among wolf-killed animals. We compared HCC between different mortality sources for bison (wolf-killed n= 20 or human-harvested n =23) and found that HCC was significantly elevated in wolf-killed bison (¯ = 7.56 ± 1.35pg/mg). We found that HCC, species, sex and snow depth were all significant predictor variables of marrow lipid content of bison (n= 14), moose (n= 11) and deer (n= 27). Bison displayed the strongest negative correlation between HCC and marrow lipid content (r2= 0.31). Our results suggest that chronic stress and poor body condition make prey more vulnerable to predation by wolves. HCC and marrow lipid content can provide reliable indicators of the physiological response of animals to stressors and may provide information on expected predator success that can be used to predict predator population dynamics.
Highlights
In vertebrates, adverse stressors cause the release of glucocorticoids (GCs) from the adrenal cortex via the hypothalamic– pituitary–adrenal (HPA) axis (Creel et al, 2009)
We evaluated the link between chronic stress, body condition and vulnerability to predation by gray wolves (Canis lupus) in bison (Bison bison bison), moose (Alces alces) and white-tailed deer (Odocoileus virginianus) in Prince Albert National Park (PANP), Saskatchewan, Canada
Wolf-killed bison had significantly higher hair cortisol concentration (HCC) than humanharvested bison, and mortality source was the best predictor of HCC in bison
Summary
Adverse stressors cause the release of glucocorticoids (GCs) from the adrenal cortex via the hypothalamic– pituitary–adrenal (HPA) axis (Creel et al, 2009). GCs, such as cortisol, cause behavioural and/or physiological responses that form an adaptive stress response by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Acute stress is an immediate adaptive response to adverse stimuli with short-term physiological effects, but chronic or repeated activation of the stress response can be maladaptive and negatively affect growth, reproduction and cognitive ability, increase catabolism of stored energy and depress immune activity (Boonstra et al, 1998; Sapolsky et al, 2000; Kitaysky et al, 2003; Charmandari et al, 2005; Macbeth et al, 2010)
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