Endangered , apparently : th e role of ap

C onservation biologists have reported grow ing evidence o f food-w eb in te rac­ tions as causes o f species endangerm ent. A pparen t com petition is an indirect in terac tion am ong prey species m ediated by a shared p reda to r, and has been increasingly linked to declines o f prey species across taxa. W e review theoretical and em pirical studies o f ap p aren t com petition , w ith specific a tten tio n to the m echanism s of asym m etry am ong apparen tly com peting prey species. A sym ­ m etry is theoretically driven by niche overlap, species fitness tra its, spatial heterogeneity and generalist p red a to r behavior. In real-w orld systems, hum aninduced changes to ecosystems such as h ab ita t a lte ra tion and in troduced species m ay be u ltim ate sources o f species endangerm ent. H ow ever, ap p aren t com peti­ tion is show n to be a proxim ate m echanism w hen resu ltan t changes in troduce or subsidize ab u n d an t p rim ary prey fo r p red a to r populations. D em onstra tion of ap p aren t com petition is difficult due to the indirect re lationships betw een prey and p red a to r species and the po ten tia l fo r concurren t exploitative com petition or o ther com m unity effects. H ow ever, general conclusions are d raw n concerning the characteristics o f prey and p red a to r species likely to exhibit asym m etric ap p aren t com petition , and the options for recovering endangered species. W hile short-term m anagem ent m ay be required to avoid im m inent extinction in systems dem onstrating ap p aren t com petition , we propose adaptive conservation efforts d irected a t long-term recovery.