Incidental predation, enemy-free space and the coexistence of incidental prey

摘要

Many communities consist of a generalist predator that consumes multiple prey species whose persistence is thereby threatened through the indirect effect of apparent competition. However, uncommon and/or ephemeral prey may be encountered only incidentally through the predator's effort expended to consume primary prey. In such instances, the functional response to incidental prey is driven entirely through the density of primary prey. Moreover, rarity and brevity in the predator's diet precludes a numerical response to incidental prey. Instead, the persistence of incidental prey may be critically linked to gaps in space unexploited by predators, i.e. enemy-free space. I use optimal foraging theory to derive a mechanism by which enemy-free space is created as a result of a predator's forging aptitude and patch-use behavior. In non-competitive environments enemy-free space provides a behavioral refuge for incidental prey that may prevent their extinction. In competitive environments, greater enemy-free space is associated with higher incidental prey densities and concomitantly greater competitive effects. As a result, incidental prey diversity declines with an increase in enemy-free space.