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‐km² 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 km²), 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 km²). Wolf density (3.1 wolves/1,000 km²) and pack sizes ( = 4.0 wolves/pack) were low and resident (established) territories were large ( = 4,360 km²; 100% minimum convex polygon). The low density of wolves mirrored the low (standardized) ungulate biomass index (UBI; moose + boreal caribou) of the study area (0.36 UBI/km²). We conclude that wolf and hence caribou populations were not responding in accordance with the outcomes generally predicted by DMAC in our study area because the requisite strong, positive response to fire of deciduous‐browse and alternate‐prey abundance was lacking. As a limiting factor to caribou, DMAC is likely modulated at a macroecological scale by factors such as net primary productivity, a corollary to the general hypothesis that we advance here (i.e., primary productivity hypothesis of DMAC). We caution against managing for caribou based on the presumption of DMAC where the mechanism does not apply, which may include much of boreal caribou range in the north. © 2020 The Wildlife Society.

中文翻译：

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在北北方驯鹿场中以干扰为媒介的明显竞争解耦

对林地北美驯鹿（Rangifer tarandus caribou；北美驯鹿）的北方和山区种群的威胁最广泛报道涉及栖息地或干扰介导的表观竞争（DMAC）。通过DMAC，人们认为自然和人为干扰会增加落叶浏览的子宫颈（例如，驼鹿[ Alces alces ]，鹿[ Odocoileus spp。]）的数量，从而促进捕食者（尤其是狼[ Canis lupus]]）数字，从而增加了驯鹿捕食的风险。我们最了解DMAC对北美驯鹿的影响，在该物种中，该物种受到生产力相对较高的南部北方和山区系统的人为活动的威胁。然而，北美现存的北北驯鹿范围中，> 60％由生产力低下的北部盾构和塔加羚羊生态区组成，在DMAC的背景下，北美驯鹿可能仅与1个有蹄类动物竞争（驼鹿）。在这种环境下，我们几乎不了解DMAC如何作为驯鹿的限制因素。2014-2018年，在加拿大萨斯喀彻温省，结合植被采样，航空测量和遥测数据（n  = 38头狼），我们在87,193-km范围内搜索了DMAC的证据（与假设相符的数据趋势）。²西北部实地盾构的一个地区，一个生产力低下但原始的地区（被归类为人为土地的土地面积的0.18％）具有历史上很高的回火间隔（47％年龄小于40岁的林分）。尽管干扰程度很高，但驼鹿密度仍然相对较低（47驼鹿/ 1,000 km ²），这可能是由于落叶林或混木林林分稀少，以及占主导地位的年轻针叶林林分的落叶林浏览量低。相反，该物种的北美驯鹿密度相对较高（37驯鹿/ 1,000 km ²）。狼密度（3.1狼/ 1,000 km ²）和群大小（ = 4.0狼/群）低，而居民（既定）地区则大（ = 4,360 km ²; 最小100％的凸多边形）。低密度的狼反映了研究区域的低（标准化）有蹄类动物生物量指数（UBI；驼鹿+北方驯鹿）（0.36 UBI / km ²）。我们得出的结论是，狼和因此的驯鹿种群没有按照DMAC在我们研究区域中普遍预测的结果做出反应，因为缺乏对落叶弓箭和猎物丰富的火的必要的强而积极的反应。作为驯鹿的限制因素，DMAC可能在宏观生态规模上受到净初级生产力等因素的调节，这是我们在此提出的一般假设（即，DMAC的初级生产力假设）的推论。我们警告不要在不适用该机制的情况下基于DMAC的假设来管理驯鹿，其中可能包括北部的许多北方驯鹿范围。©2020野生动物协会。