Data from: Realized trophic niche driven by apparent competition: an example with marsupials

According to apparent competition theory, the co-occurrence of two species that share the same predators appears to affect each other's population growth and abundance. However, due to habitat loss and over-hunting, top predators are being made rare worldwide. Considering that apparent competitors share similar resources, we would expect the absence of top predators to reflect in changes on prey realized trophic niches. To test our hypothesis, we developed a model to predict the abundance ratio of apparent competitor species based on changes in their realized trophic niches. We tested our model against field data on the Neotropical marsupials Didelphis aurita and Metachirus nudicaudatus. Our results revealed that D. aurita and M. nudicaudatus are two species under apparent competition and their realized trophic niche and diet overlap change according to the presence of top predators. The model was able to predict the actual relative abundances of D. aurita and M. nudicaudatus in the three empirical studies analyzed. Our study presents quantitative support to the apparent competition theory; however, the model's applications to other groups still need to be verified. Additionally, our study shows that the lack of top predators has consequences on the realized trophic niche of their prey, and therefore, we reinforce that conservation plans need to focus on the effects of top predator loss on ecosystems.

根据表观竞争（apparent competition）理论，共享同一捕食者的两个物种种群共存时，似乎会相互影响对方的种群增长与丰度。然而，受栖息地丧失与过度捕猎影响，全球范围内的顶级捕食者（top predators）正日渐稀少。鉴于表观竞争者共享相似资源，我们推测，顶级捕食者的缺失会反映在猎物的实际营养生态位（realized trophic niche）变化中。为验证这一假说，我们构建了一个模型，可基于表观竞争者的实际营养生态位变化预测其物种间的丰度比。我们以新热带界有袋类（Neotropical marsupials）中的白耳负鼠（Didelphis aurita）与裸尾负鼠（Metachirus nudicaudatus）的野外数据对模型进行了检验。研究结果显示，白耳负鼠与裸尾负鼠确实处于表观竞争关系中，二者的实际营养生态位与食性重叠程度会随顶级捕食者的存在与否发生改变。在本研究分析的三项实证研究中，该模型均可准确预测白耳负鼠与裸尾负鼠的实际相对丰度。本研究为表观竞争理论提供了定量支撑，但该模型应用于其他类群的有效性仍有待验证。此外，本研究证实顶级捕食者的缺失会对猎物的实际营养生态位产生影响，因此我们呼吁，保护规划应重点关注顶级捕食者丧失对生态系统造成的连锁效应。