Interacting effect of wolves and climate on recruitment in a northern mountain caribou population

Abstract

There is limited research on the influence of Pacific‐based climate in large herbivore populations. Additionally, much of our understanding on the effect of large‐scale climate on ungulate population dynamics has occurred on forage‐limited rather than predator‐limited populations. We compared the influence of the Pacific Decadal Oscillation (PDO), North Pacific Index, and local weather on recruitment in a predator‐limited mountain‐dwelling caribou Rangifer tarandus caribou population in the Yukon Territory, Canada, across a range of wolf Canis lupus densities. A large‐scale wolf removal program allowed us to examine the role of Pacific climate and weather when wolves were reduced to ∼15% of their pre‐removal levels. Recruitment was best explained by the interaction of wolf density and April‐PDO, with wolf density explaining the most deviance. Predicted recruitment during good springs was 0.45 (SE = 0.04) during wolf removal and 0.29 (SE = 0.03) with no wolf removal. During poor springs (low PDO, increased snow depth) predicted recruitment was 0.55 (SE = 0.10) during wolf removal and 0.12 (SE = 0.03) with no wolf removal. With non‐altered wolf densities, there was a positive relationship between April‐PDO and recruitment due to reduced snow depth at calving, allowing parturient females to disperse up in elevation away from predators. When wolf densities were substantially reduced there was a slight negative relationship between April‐PDO and recruitment, possibly due to a more rapid vegetation green‐up reducing the temporal availability of highly nutritious forage necessary for lactation and subsequent calf growth. Attempts to find general relationships between climate and ungulate population dynamics have proven difficult due to different ecological mechanisms by which climate affects individuals across populations. Temporally varying factors, such as predator density, may also play an important role in uncovering the mechanistic relationship between climate and population dynamics.

Life-history characteristics of mule deer: Effects of nutrition in a variable environment

“…The young‐to‐adult female ratio is a composite measure of several demographic processes including survival of adult females, fertility, fecundity, and survival of young (Bonenfant et al ). Although the use of ratio data for inferring population dynamics has been criticized (Caughley , McCullough ), others have used these data for characterizing demographics of ungulate populations (Raithel et al ; Harris et al ; Hegel et al , ). If reproductive rates and survival of adult females remain high with little variation, age ratios can provide a reliable index to relative changes in λ, because variation in survival of young drives interannual changes in that metric (Gaillard et al , ; Raithel et al ; Harris et al ).…”

“…Therefore, estimating the nutritional capacity for survival or recruitment should provide a reference for the degree to which mortality is compensatory or additive relative to observed survival and recruitment. Indeed, studies have demonstrated positive effects of predator removal for ungulate populations that were not resource‐limited (i.e.,those in which predation had an additive effect; Gasaway et al , Kie and White , Gasaway et al , Hegel et al , White et al ), compared with those that were resource‐limited when predator removal had little effect (i.e., those in which predation was compensatory; Bartmann et al , Ballard et al , White et al , Hurley et al ).…”

Prey Selection of Scandinavian Wolves: Single Large or Several Small?

“…Although larger prey animals are more profitable, they may also cause a higher effort and risk of injury or death to the predator [10, 11, 12]. In addition, environmental conditions may also impact on the effort involved for the predator to encounter prey animals, and the efficiency by which the prey animal may escape an attack, i.e., their vulnerability [12, 13, 14]. …”

Environmental factors shaping ungulate abundances in Poland

“…Among density-independent factors, weather conditions have significant and multidirectional effects on ungulate demography, operating mainly through changes in mortality or indirectly through the quantity and quality of food (Post and Stenseth 1999; Hone and Clutton-Brock 2007). For example, harsh winter conditions affected the survival rate of Soay sheep (Milner et al 1999; Coulson et al 2001), red deer ( Cervus elaphus ; Forchhammer et al 1998), and roe deer ( Capreolus capreolus ; Gaillard et al 1993), and they shaped recruitment in mountain-dwelling woodland caribou ( Rangifer tarandus caribou ; Hegel et al 2010). Autumn weather influenced reproduction rates of female white-tailed deer ( Odocoileus virginianus ), while spring weather conditions affected their reproductive success (Simard et al 2010).…”