Burley Louise A, Moyer Anna T, Petranka James W
Department of Biology, University of North Carolina at Asheville, One University Heights, Asheville, NC 28804, USA.
Oecologia. 2006 Jul;148(4):641-9. doi: 10.1007/s00442-006-0398-z. Epub 2006 Mar 3.
Intraguild predation (IGP) is common in most communities, but many aspects of density-dependent interactions of IG predators with IG prey are poorly resolved. Here, we examine how the density of an IG predator can affect feeding group size, IG egg predation, and the growth responses of IG prey. We used laboratory feeding trials and outdoor mesocosm experiments to study interactions between a social intraguild predator (larvae of the wood frog; Rana sylvatica) and its prey (spotted salamander; Ambystoma maculatum). Larvae of R. sylvatica could potentially affect A. maculatum by consuming shared larval food resources or by consuming eggs and hatchlings. However, successful egg predation requires group feeding by schooling tadpoles. We established from five to 1,190 hatchlings of R. sylvatica in mesocosms, then added either 20 A. maculatum hatchlings to study interspecific competition, or a single egg mass to examine IGP. Crowding strongly suppressed the growth of R. sylvatica, and IGP was restricted to the egg stage. In the larval competition experiment, growth of A. maculatum was inversely proportional to R. sylvatica density. In the predation experiment, embryonic mortality of A. maculatum was directly proportional to the initial density of R. sylvatica and the mean number of tadpoles foraging on egg masses. IGP on eggs reduced A. maculatum hatchling density, which accelerated larval growth. Surprisingly, the density of R. sylvatica had no overall effect on A. maculatum growth because release from intraspecific competition via egg predation was balanced by increased interspecific competition. Our results demonstrate that the density of a social IG predator can strongly influence the nature and intensity of interactions with a second guild member by simultaneously altering the intensity of IGP and intra- and interspecific competition.
集团内捕食（IGP）在大多数群落中很常见，但IG捕食者与IG猎物之间密度依赖性相互作用的许多方面仍未得到很好的解决。在这里，我们研究了IG捕食者的密度如何影响觅食群体大小、IG卵捕食以及IG猎物的生长反应。我们使用实验室饲养试验和室外中型生态系统实验来研究一种社会性集团内捕食者（林蛙；Rana sylvatica的幼虫）与其猎物（虎纹钝口螈；Ambystoma maculatum）之间的相互作用。林蛙的幼虫可能通过消耗共享的幼虫食物资源或通过消耗卵和幼体来影响虎纹钝口螈。然而，成功的卵捕食需要成群的蝌蚪进行集体觅食。我们在中型生态系统中放入5到1190只林蛙幼体，然后添加20只虎纹钝口螈幼体以研究种间竞争，或者添加单个卵块以检验集团内捕食。拥挤强烈抑制了林蛙的生长，并且集团内捕食仅限于卵期。在幼虫竞争实验中，虎纹钝口螈的生长与林蛙密度成反比。在捕食实验中，虎纹钝口螈的胚胎死亡率与林蛙的初始密度以及在卵块上觅食的蝌蚪平均数量成正比。对卵的集团内捕食降低了虎纹钝口螈幼体的密度，这加速了幼虫的生长。令人惊讶的是，林蛙的密度对虎纹钝口螈的生长没有总体影响，因为通过卵捕食从种内竞争中释放出来的效应被种间竞争的增加所平衡。我们的结果表明，社会性集团内捕食者的密度可以通过同时改变集团内捕食以及种内和种间竞争的强度，强烈影响与第二个群落成员相互作用的性质和强度。
