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 appear to affect each other’s
population growth and abundance. However, as a result of habitat loss and
over-hunting, top predators are being made rare worldwide. Taking into
account 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.

根据表观竞争理论（apparent competition theory），共享同一捕食者的两个物种种群共存时，会彼此影响对方的种群增长与种群丰度。然而，受栖息地丧失与过度捕猎的影响，全球范围内的顶级捕食者种群正日渐稀少。鉴于表观竞争者共享相似的资源，我们可推测顶级捕食者的缺失会反映在猎物实际营养生态位的变化中。为验证这一假说，我们构建了模型，基于表观竞争者的实际营养生态位变化，预测其物种丰度比值。我们以新热带区有袋类动物褐耳负鼠（Didelphis aurita）与裸足负鼠（Metachirus nudicaudatus）的野外数据对模型进行了检验。研究结果显示，褐耳负鼠与裸足负鼠正处于表观竞争关系中，二者的实际营养生态位与饮食重叠程度会随顶级捕食者的存在与否发生改变。该模型能够准确预测本次分析的三项实证研究中，褐耳负鼠与裸足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，但该模型对其他类群的适用性仍有待验证。此外，本研究表明顶级捕食者的缺失会对其猎物的实际营养生态位产生影响，因此我们进一步强调，保护规划需聚焦于顶级捕食者丧失对生态系统造成的影响。