Serrouya Robert, McLellan Bruce N, van Oort Harry, Mowat Garth, Boutin Stan
Columbia Mountains Caribou Research Project, Revelstoke, British Columbia, Canada.
Alberta Biodiversity Monitoring Institute, University of Alberta, Edmonton, Alberta, Canada.
PeerJ. 2017 Aug 29;5:e3736. doi: 10.7717/peerj.3736. eCollection 2017.
The expansion of moose into southern British Columbia caused the decline and extirpation of woodland caribou due to their shared predators, a process commonly referred to as apparent competition. Using an adaptive management experiment, we tested the hypothesis that reducing moose to historic levels would reduce apparent competition and therefor recover caribou populations. Nested within this broad hypothesis were three specific hypotheses: (1) sport hunting could be used to substantially reduce moose numbers to an ecological target; (2) wolves in this ecosystem were primarily limited by moose abundance; and (3) caribou were limited by wolf predation. These hypotheses were evaluated with a before-after control-impact (BACI) design that included response metrics such as population trends and vital rates of caribou, moose, and wolves. Three caribou subpopulations were subject to the moose reduction treatment and two were in a reference area where moose were not reduced. When the moose harvest was increased, the moose population declined substantially in the treatment area (by 70%) but not the reference area, suggesting that the policy had the desired effect and was not caused by a broader climatic process. Wolf numbers subsequently declined in the treatment area, with wolf dispersal rates 2.5× greater, meaning that dispersal was the likely mechanism behind the wolf numerical response, though reduced recruitment and starvation was also documented in the treatment area. Caribou adult survival increased from 0.78 to 0.88 in the treatment area, but declined in the reference. Caribou recruitment was unaffected by the treatment. The largest caribou subpopulation stabilized in the treatment area, but declined in the reference area. The observed population stability is comparable to other studies that used intensive wolf control, but is insufficient to achieve recovery, suggesting that multiple limiting factors and corresponding management tools must be addressed simultaneously to achieve population growth.
驼鹿向不列颠哥伦比亚省南部扩张，导致林地驯鹿数量减少和灭绝，原因是它们有共同的捕食者，这一过程通常被称为似然竞争。通过一项适应性管理实验，我们检验了以下假设：将驼鹿数量减少到历史水平将减少似然竞争，从而使驯鹿种群数量得以恢复。在这个宽泛的假设中包含三个具体假设：（1）狩猎可以大幅减少驼鹿数量，使其达到生态目标；（2）该生态系统中的狼主要受驼鹿数量的限制；（3）驯鹿受狼捕食的限制。这些假设通过前后对照影响（BACI）设计进行评估，该设计包括驯鹿、驼鹿和狼的种群趋势及生命率等响应指标。三个驯鹿亚种群接受了驼鹿数量减少处理，另外两个处于未减少驼鹿数量的参考区域。当驼鹿狩猎量增加时，处理区域的驼鹿种群数量大幅下降（下降了70%），而参考区域没有下降，这表明该政策产生了预期效果，且不是由更广泛的气候过程导致的。随后，处理区域的狼数量下降，狼的扩散率提高了2.5倍，这意味着扩散是狼数量响应背后的可能机制，不过处理区域也记录到繁殖减少和饥饿现象。处理区域驯鹿的成年存活率从0.78提高到了0.88，但参考区域的成年存活率下降了。驯鹿的繁殖不受该处理的影响。最大的驯鹿亚种群在处理区域数量稳定，但在参考区域数量下降。观察到的种群稳定性与其他采用强化狼控制措施的研究相当，但不足以实现种群数量的恢复，这表明必须同时解决多个限制因素及相应的管理工具，才能实现种群增长。
