Anthropogenic Disturbance Mediates Trophic Niche Overlap Between Sympatric Generalist Predators

Human activities generally increase trophic overlap in predator guilds through resource subsidies, whereas the effects on whether sympatric species overlap or separate their niches are context-dependent. Mesocarnivores (order Carnivora, Mammalia) are often adaptive and tolerant to human activities, allowing them to establish populations in human-modified landscapes. Here, we examined how trophic niche overlaps between the wide-ranging mesocarnivores, the red fox (Vulpes vulpes) and sympatric martens (genus Martes), are influenced by geo-environmental and anthropogenic factors, using a systematic literature review and meta-analysis at the Eurasian continental scale. We hypothesized that the extent of trophic overlap would increase in areas with greater human disturbance and less productive environments associated with resource availability. We included a total of 35 publications with 76 observations from continental Europe and Japan and then calculated the relative trophic overlap. Their trophic overlaps were relatively high because they shared common resources, such as small mammals, invertebrates, and fruits. Contrary to our predictions, multivariate statistical modeling demonstrated that trophic overlaps declined with increasing human disturbance and decreasing vegetative landscapes. Our findings indicate that human disturbances forced their resource use to separate, potentially due to resource depletion by land modifications and intense human activities, whereas vegetated habitats moderated direct and indirect competition. Based on these results, we conclude that patterns in trophic interactions largely depend on spatiotemporal resource availabilities. We suggest that maintaining regional resource abundance is crucial for successful sympatry in competing carnivores and for balancing stable intraguild interactions in human-modified landscapes.