Cougar predation and population growth of sympatric mule deer and white-tailed deer

Abstract

Mule deer (Odocoileus hemionus) populations throughout the west appear to be declining, whereas whitetailed deer (Odocoileus virginianus) populations are increasing. We compared abundance, number of fetuses per female (maternity rate), recruitment, and cause-specific adult (≥1 year old) mortality rate for sympatric mule deer and whitetailed deer in south-central British Columbia to assess population growth for each species. White-tailed deer were three times more abundant (908 ± 152) than mule deer (336 ± 122) (mean ± 1 SE). Fetal rates of white-tailed deer (1.83) were similar to those of mule deer (1.78). There was no statistically significant difference in recruitment of white-tailed deer (56 fawns : 100 does) and mule deer (38 fawns : 100 does). The annual survival rate for adult white-tailed deer (S WT = 0.81) was significantly higher than that for mule deer (S MD = 0.72). The main cause of mortality in both populations was cougar predation. The lower mule deer survival rate could be directly linked to a higher predation rate (0.17) than for white-tailed deer (0.09). The finite growth rate (λ) was 0.88 for mule deer and 1.02 for white-tailed deer. The disparate survival and predation rates are consistent with the apparent-competition hypothesis.Résumé : Les populations de cerfs mulets (Odocoileus hemionus) semblent être en déclin dans tout l'ouest, alors que celles des cerfs de Virginie (Odocoileus virginianus) augmentent. Nous avons comparé l'abondance, le taux de production de fétus, le taux de recrutement et les taux de mortalité des adultes ($1 an) attribuables à des causes spécifiques chez des cerfs mulets er des cerfs de Virginie vivant en sympatrie dans le centre sud de la Colombie-Britannique afin d'évaluer la croissance démographique de chacune de ces espèces. Les cerfs de Virginie sont trois fois plus abondants (908 ± 152) que les cerfs mulets (336 ± 122) (moyenne ± 1 erreur type). Le taux foetal est semblable chez les cerfs de Virginie (1,83) et les cerfs mulets (1,78). Il n'y a pas de différence statistiquement significative entre les taux de recrutement des cerfs de Virginie (56 faons : 100 femelles) et des cerfs-mulets (38 faons : 100 femelles). La survie annuelle des adultes est significativement plus élevée chez le cerf de Virginie (S WT = 0,81) que chez le cerf mulet (S MD = 0,72). La principale cause de mortalité chez les deux populations est la prédation exercée par les couguars. Le taux de survie plus faible du cerf mulet peut être relié directement à son taux de prédation plus élevé (0,17) que celui du cerf de Virginie (0,09). Le taux de croissance réel (8) est de 0,88 chez le cerf mulet et de 1,02 chez le cerf de Virginie. La disparité des taux de prédation et de survie est en accord avec l'hypothèse de la compétition apparente.[Traduit par la Rédaction] Robinson et al. 568

Prey Behavior, Age‐Dependent Vulnerability, and Predation Rates

“…If coyotes live in an area with a preferred prey species that is readily available in winter (e.g., snowshoe hares [Lepus americanus]), we would expect coyotes to reduce the time spent hunting ungulates in winter, which should benefit mule deer. As with other forms of alternative prey (Patterson et al 1998;Cooper et al 1999;Ackerman 2002;Prugh 2005;Miller et al 2006), the presence of the second deer species would be likely to influence predation on the first (Robinson et al 2002) and should be considered in future models.…”

Effects of Simulated Mountain Lion Caching on Decomposition of Ungulate Carcasses

“…Times and locales preferred for hunting are clearly relevant to assessing and managing the risks to humans that are increasingly of concern to managers. Under certain circumstances, mountain lion predation can limit bighorn sheep (Ovis canadensis), have potentially deleterious impacts on vulnerable pronghorn (Antilocapra americana), and potentially regulate mule deer (Odocoileus hemionus) and other ungulate populations (Ockenfels 1994, Hayes et al 2000, Logan and Sweanor 2001, Robinson et al 2002, Rominger et al 2004). These direct effects on populations of herbivores potentially translate into indirect effects on vegetation structure and composition (Ripple and Beschta 2006).…”

Effects of Cougar Predation and Nutrition on Mule Deer Population Declines in the Intermountain Province of the Columbia Basin, 2001-2002 Annual Report.

“…Details for obtaining estimates of vital rates from telemetry data are given in Wielgus and Bunnell (1994a and Robinson and Wielgus (2000). Details for estimating population growth from vital rates are given in Wielgus (2002), Wielgus et al (2001), and Robinson et al (2002). Densities of mule deer and white-tailed deer in treatment and control areas will be determined using seasonal and annual aerial surveys.…”

“…The Columbia Basin Fish & Wildlife Compensation Program in British Columbia contracted Wielgus to determine if mule deer were declining and the possible cause of the decline if any. Working in the NE IM and adjacent Canadian portions of the Columbia Basin, Robinson et al (2002) found that mule deer populations were decreasing at a finite rate of growth of R = 0.88 (declining at 12%/year) from 1997-2000. During the same time, sympatric white-tailed deer were increasing at R = 1.02.…”