The dual influence of top‐down and bottom‐up processes on a mesopredator and the consequences for prey

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Abstract
Ecosystem dynamics are shaped by interacting top‐down and bottom‐up processes, yet their relative importance may vary through time following disturbances such as disease outbreaks and changes in apex predator communities. Using a 52‐year time series in south‐central Sweden, we examined how disease, apex predators, and prey availability jointly impact a mesopredator, the red fox Vulpes vulpes , and how these dynamics propagate to secondary prey. Potential drivers of fox dynamics (number of litters) were vole Clethrionomys glareolus and Microtus agrestis abundance, sarcoptic mange outbreaks, and the re‐establishment of Eurasian lynx Lynx lynx and wolves Canis lupus , and we assessed potential subsequent effects on hare Lepus europaeus and L. timidus and woodland grouse Lyrurus tetrix and Tetrao urogallus densities. Fox litter numbers were positively associated with vole abundance throughout the study period, indicating persistent bottom‐up regulation. In contrast, top‐down effects were evident through reductions in the number of fox litters during sarcoptic mange outbreaks and following the simultaneous presence of lynx and wolves. Support for the mesopredator release hypothesis was context‐dependent: densities of secondary prey increased during the mange outbreak but declined after apex predator re‐establishment, despite reduced number of fox litters. Moreover, the characteristic synchrony between voles and secondary prey weakened following the return of apex predators, suggesting direct and indirect effects beyond mesopredator suppression. Our results demonstrate that fox reproduction is regulated by concurrent top‐down and bottom‐up processes and that apex predator recovery can alter trophic relationships and not only reverse mesopredator release.

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