Disturbance‐Mediated Apparent Competition Decouples in a Northern Boreal Caribou Range

• Published in: The Journal of Wildlife Management
• Main Authors: Neufeld, Branden T., Superbie, Clara, Greuel, Ruth J., Perry, Thomas, Tomchuk, Patricia A., Fortin, Daniel, McLoughlin, Philip D.
• Other Authors: Natural Sciences and Engineering Research Council of Canada
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2020
• Subjects: Canada; Caribou Range; Alces alces; Canis lupus; Rangifer tarandus; taiga
• Online Access: http://dx.doi.org/10.1002/jwmg.21982; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jwmg.21982; https://onlinelibrary.wiley.com/doi/full-xml/10.1002/jwmg.21982

ABSTRACT The most widely reported threat to boreal and mountain populations of woodland caribou ( Rangifer tarandus caribou caribou) involves habitat‐ or disturbance‐mediated apparent competition (DMAC). With DMAC, natural and anthropogenic disturbances that increase the abundance of deciduous‐browsing cervids (e.g., moose [ Alces alces ], deer [ Odocoileus spp.]) are thought to promote predator (especially wolf [ Canis lupus ]) numbers, which heightens predation risk to caribou. We know most about the effects of DMAC on caribou where the species is under threat by anthropogenic activities in relatively productive southern boreal and mountain systems. Yet, >60% of extant boreal caribou range in North America consists of northern shield and taiga ecoregions of low productivity where caribou may compete with only 1 ungulate species (moose) in the context of DMAC. In this environment, we know very little of how DMAC acts as a limiting factor to caribou. In Saskatchewan, Canada, from 2014–2018, using a combination of vegetation sampling, aerial surveys, and telemetry data ( n = 38 wolves), we searched for evidence of DMAC (trends in data consistent with the hypothesis) in an 87,193‐km 2 section of the Western Boreal Shield, a poorly productive but pristine region (0.18% of land cover classed as an anthropogenic feature) with a historically high fire‐return interval (47% of stands aged <40 years). Despite the high levels of disturbance, moose density was relatively low (47 moose/1,000 km 2 ), likely because of the scarcity of deciduous or mixed‐wood stands and low abundance of deciduous browse in the young conifer stands that dominated the landscape. In contrast, boreal caribou density was relatively high for the species (37 caribou/1,000 km 2 ). Wolf density (3.1 wolves/1,000 km 2 ) and pack sizes ( = 4.0 wolves/pack) were low and resident (established) territories were large ( = 4,360 km 2 100% minimum convex polygon). The low density of wolves mirrored the low (standardized) ungulate biomass index (UBI; ...