A nutritionally mediated risk effect of wolves on elk

Article · April 2010with138 Reads
DOI: 10.1890/09-0221.1 · Source: PubMed
Abstract
Though it is widely argued that antipredator responses carry nutritional costs, or risk effects, these costs are rarely measured in wild populations. To quantify risk effects in elk, a species that strongly responds to the presence of wolves, we noninvasively monitored diet selection and nutrient balance in wintering elk in the Upper Gallatin, Montana, USA, over three winters while quantifying the local presence of wolves at a fine spatiotemporal scale. Standard nutritional indices based on the botanical and chemical composition of 786 fecal samples, 606 snow urine samples, and 224 forage samples showed that elk were generally malnourished throughout winter. Increased selection for dietary nitrogen within forage types (e.g., grasses) led to approximately 8% higher fecal nitrogen in the presence of wolves. However, urinary allantoin : creatinine and potassium : creatinine ratios decreased in the presence of wolves, suggesting large declines in energy intake, equal to 27% of maintenance requirements. Urinary nitrogen : creatinine ratios confirmed that deficiencies in nitrogen and/or energy were exacerbated in the presence of wolves, leading to increased endogenous protein catabolism. Overall, the nutritional effects of wolf presence may be of sufficient magnitude to reduce survival and reproduction in wintering elk. Nutritionally mediated risk effects may be important for understanding predator-prey dynamics in wild populations, but such effects could be masked as bottom-up forces if antipredator responses are not considered.
  • ...Despite this general pattern, there has been debate over the costs of increased antipredator defenses in ungulates. Ungulates commonly respond to increased predation risk with increased vigilance, altered patterns of aggregation, reduced foraging, retreat to safe habitats, and altered diets (Prins and Iason 1989, Hunter and Skinner 1998, Caro 2005, Creel et al. 2005, 2014, Valeix et al. 2009, Christianson and Creel 2010, Periquet et al. 2012, Barnier et al. 2014). In some ungulates, these responses are associated with reduced reproduction (Creel et al. 2007, Cherry et al. 2016) as in other taxa (Peckarsky et al. 1993, Boonstra et al. 1998, Zanette 2003, Pangle et al. 2007, Zanette et al. 2011). ...
  • ...In contrast, field experiments on elk suggest that exposure to predators does not change fecal glucocorticoid concentrations, but does affect their foraging patterns and habitat selection and extends to affecting breeding ( Creel et al. 2009, Christlanson andCreel 2010). Boonstra (2013) claims that predator-induced stress response is "an adaptive trait selected for under certain life histories" (Boonstra 2013, p. 20). ...
  • ...Spatial heterogeneity in predation risk and corresponding behavioral adjustments of prey give rise to " a landscape of fear " (Laundré et al. 2001Laundré et al. , 2014), which might then influence ecosystem structure and function (Ripple et al. 2001;Ripple and Beschta 2006;Kuijper et al. 2013). Predator-induced behavioral adjustments by prey might involve energetic costs and physiological responses (Creel et al. 2007;Barnier et al. 2014) that can ultimately affect prey demography (Creel and Christianson 2008;Christianson and Creel 2010;Zanette et al. 2011). Indeed, predators could have a greater effect on prey demography through fear than through direct consumption of individual prey (Preisser et al. 2005). ...
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