Predation risk for boreal woodland caribou in human-modified landscapes: Evidence of wolf spatial responses independent of apparent competition.

Abstract Management of wildlife often relies upon understanding mechanisms linking anthropogenic disturbance to population declines. The most-cited mechanism by which disturbance threatens boreal caribou (Rangifer tarandus caribou) is the exacerbation of apparent competition via increases in early successional forage, and subsequent changes in the densities and distributions of other prey species and gray wolves (Canis lupus). An alternative mechanism is the direct alteration of wolf distribution via positive responses by wolves to anthropogenic features. We conducted a mechanistic evaluation of hypotheses explaining human-mediated increases in boreal caribou mortality across northeast British Columbia. We evaluated support for (i) numeric apparent competition (increased prey densities) by evaluating relationships between disturbances, moose (Alces alces) density, and caribou survival. To evaluate (ii) spatial apparent competition (altered prey distribution) and (iii) wolf spatial responses (altered wolf distribution independent of prey), we modeled the relationships between disturbances and indices of caribou-moose and caribou-wolf co-occurrence and then examined predation risk for caribou as a function of co-occurrence. We did not detect any relationships between anthropogenic disturbances, moose density, and caribou survival. Although caribou-moose co-occurrence increased predation risk, we observed both positive and negative relationships between disturbances and caribou-moose co-occurrence. In contrast, caribou-wolf co-occurrence increased predation risk and was positively correlated with anthropogenic linear features. Contrary to other boreal caribou populations, our analyses demonstrate stronger support for the direct effects of anthropogenic linear features on caribou-wolf spatial overlap, leading to greater risk for caribou. Our research highlights the need for region-specific management actions to conserve and recover widely distributed species. Highlights • Boreal caribou are federally listed as threatened across their range as a result of resource extraction • Human-mediated apparent competition with other prey species is theorized as the primary mechanism of decline • In northeast British Columbia, the effect of anthropogenic linear features on caribou-wolf encounters is better supported • Limiting future and restoring existing linear features is recommended for caribou recovery in northeast British Columbia • Regional management actions are often necessary for the conservation of widely distributed species [ABSTRACT FROM AUTHOR]