The commonness of omnivory in natural communities is puzzling, because simple dynamic
models of tri-trophic systems with omnivory are prone to species extinction. In particular, the
intermediate consumer is frequently excluded by the omnivore at high levels of enrichment.
It has been suggested that adaptive foraging by the omnivore may facilitate coexistence,
because the intermediate consumer should persist more easily if it is occasionally dropped
from the omnivore's diet. We explore theoretically how species permanence in tri-trophic …