Insect-mediated apparent competition between mammals in a boreal food web

Significance Despite the growing recognition that indirect interactions within species networks can determine food web dynamics, empirical evidence remains rare. We demonstrate how the impact of insects on forest structure and composition can reverberate across trophic levels by altering apparent competition in a large-mammal food web subjected to timber extraction. Spruce budworm outbreaks initiated a flush in deciduous vegetation that benefited moose, which translated into apparent competition between moose and boreal caribou through wolf predation. Mortality risk of caribou became indirectly related to patterns of insect and human activities, with the ungulate experiencing higher risk when selecting stands severely infested by budworms and subsequently logged. We expose cascading effects of insect–forest interactions on large-mammal relations in human-altered ecosystems.