Data from: Using predator-prey theory to predict outcomes of broad-scale experiments to reduce apparent competition

Apparent competition is an important process influencing many ecological communities. We used predator-prey theory to predict outcomes of ecosystem experiments aimed at mitigating apparent competition by reducing primary prey. Simulations predicted declines in secondary prey following reductions in primary prey because predators consumed more secondary prey until predator numbers responded to reduced prey densities. Losses were exacerbated by a higher carrying capacity of primary prey and a longer lag time of the predator’s numerical response, but a gradual reduction in primary prey was less detrimental to the secondary prey. We compared predictions against two field experiments where endangered woodland caribou (Rangifer tarandus caribou) were victims of apparent competition. First, when deer (Odocoileus sp.) declined suddenly following a severe winter, cougar (Puma concolor) declined with a 1–2-year lag, yet in the interim more caribou were killed by cougars, and caribou populations declined by 40%. Second, when moose (Alces alces) were gradually reduced using a management experiment, wolf (Canis lupus) populations declined but did not shift consumption to caribou, and the largest caribou subpopulation stabilized. The observed contrasting outcomes of sudden versus gradual declines in primary prey supported theoretical predictions. Combining theory with field studies clarified how to manage communities to mitigate endangerment caused by apparent competition that affects many taxa.表观竞争（apparent competition）是影响诸多生态群落的重要过程。我们借助捕食者-猎物理论（predator-prey theory），对旨在通过减少主要猎物以缓解表观竞争的生态系统实验结果进行了预测。模拟研究预测：在主要猎物种群数量减少后，次级猎物种群会出现下降——这是由于捕食者会更多地捕食次级猎物，直至其种群数量对猎物密度降低做出响应。主要猎物的环境容纳量（carrying capacity）越高、捕食者数值响应（numerical response）的滞后时间越长，次级猎物的种群损失便会加剧；而逐步减少主要猎物则对次级猎物的负面影响更小。 我们将理论预测与两项野外实验结果进行了对比，这两项实验中的濒危林地驯鹿（Rangifer tarandus caribou）均为表观竞争的受害类群。其一，当鹿属（Odocoileus sp.）种群在经历严冬后突然下降时，美洲狮（Puma concolor）种群会出现1~2年的滞后下降，而在此期间美洲狮对驯鹿的捕食量增加，导致驯鹿种群数量下降了40%。其二，在一项管理实验中，当驼鹿（Alces alces）种群被逐步减少时，灰狼（Canis lupus）种群出现了下降，但并未将捕食转向驯鹿，其中最大的驯鹿亚种群得以稳定。 野外观测到的主要猎物种群骤降与缓降所带来的截然不同的结果，验证了理论预测。将理论与野外研究相结合，明确了应如何调控生态群落，以缓解影响诸多类群的表观竞争所引发的物种濒危问题。