Preston Kristine L, Rotenberry John T
Department of Biology and Center for Conservation Biology, University of California, Riverside 92521, USA.
Ecology. 2006 Jan;87(1):160-8. doi: 10.1890/05-0344.
We investigated the relative importance and interaction of ecological processes affecting annual fecundity in birds by simultaneously manipulating food availability and nest predation risk in a small songbird, the Wrentit (Chamaea fasciata). From 2000 to 2002 we provided supplemental food to individual Wrentit territories, and during 2002 we altered nest predation risk by providing supplemental food to their principal predators, Western Scrub-Jays (Aphelocoma californica). These experiments were conducted during a period of high interannual variation in rainfall, with 2002 being one of the driest years on record. Food-supplemented Wrentits in a normal predation environment produced an average of 0.54 more fledglings per year than control pairs over the three breeding seasons. During the feeding plus predation manipulation experiment, Wrentit food supplementation and lowered nest predation risk each independently increased the probability that a Wrentit pair would fledge young; however, the interaction between food supplementation and altered nest predation risk was not significant. Thus, even in an extreme drought year, both food and nest predation had equal but independent effects on reproductive success and annual fecundity. Combining supplemental food with reduced nest predation did not result in a synergistic increase in annual fecundity, primarily because Wrentits did not produce multiple broods. Our results suggest that whether food and predation have additive or synergistic effects on reproductive success depends on the life history of the species and the environment in which they live.
我们通过同时操控小型鸣禽纹头雀（Chamaea fasciata）的食物可利用性和巢捕食风险，研究了影响鸟类年繁殖力的生态过程的相对重要性及其相互作用。在2000年至2002年期间，我们为纹头雀个体的领地提供补充食物，并且在2002年，我们通过为其主要捕食者加州灌丛鸦（Aphelocoma californica）提供补充食物来改变巢捕食风险。这些实验是在降雨年际变化较大的时期进行的，2002年是有记录以来最干旱的年份之一。在正常捕食环境下，补充食物的纹头雀在三个繁殖季节中每年平均比对照配对多育出0.54只雏鸟。在喂食加捕食操控实验期间，纹头雀补充食物和降低巢捕食风险各自独立增加了纹头雀配对育出幼鸟的概率；然而，补充食物与改变巢捕食风险之间的相互作用并不显著。因此，即使在极端干旱年份，食物和巢捕食对繁殖成功率和年繁殖力都有同等但独立的影响。将补充食物与降低巢捕食风险相结合并没有导致年繁殖力协同增加，主要是因为纹头雀不会产多窝卵。我们的结果表明，食物和捕食对繁殖成功是具有累加效应还是协同效应，取决于物种的生活史及其生存的环境。
