Implications of body condition on the unsustainable predation rates of endangered mountain caribou

Abstract

Both top-down and bottom-up processes influence herbivore populations, and identifying dominant limiting factors is essential for applying effective conservation actions. Mountain caribou are an endangered ecotype of woodland caribou (Rangifer tarandus caribou) that have been declining, and unsustainable predation has been identified as the proximate cause. To investigate the role of poor nutrition, we examined the influence of sex, season, age class, and available suitable habitat (i.e., old-growth forest>140 years) per caribou on bone marrow fat content of caribou that died (n = 79). Sex was the only strong predictor of marrow fat. Males that died during and post rut had lower marrow fat than females or males at other times of year. Old-growth abundance per caribou, season, and age class did not predict marrow fat. Caribou killed by predators did not have less marrow fat than those that died in accidents, suggesting that nutritionally stressed caribou were not foraging in less secure habitats or that predators selected nutritionally stressed individuals. Marrow fat in endangered and declining populations of mountain caribou was similar to caribou in other, more viable populations. Our results support previous research suggesting that observed population declines of mountain caribou are due to excessive predation that is not linked to body condition.

Straight from the caribou’s (Rangifer tarandus) mouth: detailed observations of tame caribou reveal new insights into summer–autumn diets

“…These studies, along with our own, demonstrate the need for biologically sensitive indicators to assess suitability of habitats for foraging (Searle et al 2007). Measurements of total forage or use of surrogate forage variables, such as stem density, per-capita old growth forest, landcover type, or lichen availability (Rettie and Messier 2000;Wittmer et al 2005;Metsaranta and Mallory 2007;Pinard et al 2012;McLellan et al 2012), are not able to discriminate between accepted and avoided forage biomass.…”

A review of the population dynamics of mule deer and black‐tailed deer Odocoileus hemionus in North America

“…) although results depend on predator species (Hornocker , McLellan et al. ). Other mechanisms may also be operating, since nutritional supplementation lowered predation mortality even though predators were not selecting nutritionally stressed adults in control populations (Bishop et al.…”

“…Ungulates in poor body condition take greater risks to forage (Sinclair & Arcese 1995) and prey selection of many predators can be influenced by prey body condition (e.g. Sinclair & Arcese 1995, Krumm et al 2010 although results depend on predator species (Hornocker 1970, McLellan et al 2012. Other mechanisms may also be operating, since nutritional supplementation lowered predation mortality even though predators were not selecting nutritionally stressed adults in control populations (Bishop et al 2009).…”

Biodiversity offsets and caribou conservation in Alberta: opportunities and challenges

“…Other developments such as oil sands mines completely remove caribou foraging opportunities over large areas. However, forage quantity and quality probably does not limit non-migratory caribou populations (McLellan et al, 2012). Indeed, because caribou may avoid areas of high forage quality that also have high predation risk (Briand et al, 2009), addressing the predation problem could both improve survival and recruitment and provide recovering caribou populations with additional access to high quality forage resources.…”