| Because invasive species pose tangible and often immediate threats to native biota, conservation biologists often focus on controlling or eradicating them without first understanding their ecology or functional roles in their adopted ecosystems. On San Clemente Island, California, feral cat (Felis catus) control has occurred for >20 years. Our long-term dietary analyses revealed a strong preference for native rodents, transition to reptilian and avian prey when rodents declined, and substantial cumulative impacts on the vertebrate prey base. We used GPS collars to examine home-range, habitat use, and to evaluate population control efficacy. Cementum annuli age estimates and population reconstruction analyses revealed a relatively stable population with some individuals living >15 years. In addition to direct effects through predation, we found cats likely compete for resources in both time and space with endemic island foxes (Urocyon littoralis) and endangered San Clemente loggerhead shrikes (Lanius ludovicianus mearnsi). Cats are more robust to removal techniques than was previously thought, and individuals may persist for many years despite the seemingly harsh environment and intensive control program. Our findings provide insight into interactions with native species, allow us to evaluate the feasibility and possible cascade effects of eradication, and inform future conservation efforts. |