Araújo Márcio S, Guimarães Paulo R, Svanbäck Richard, Pinheiro Aluisio, Guimarães Paulo, Dos Reis Sérgio F, Bolnick Daniel I
Departamento de Parasitologia, Programa de Pós-Graduação em Ecologia, Instituto de Biologia, Universidade Estadual de Campinas, CP 6109, 13083-970, Campinas, SP, Brazil.
Ecology. 2008 Jul;89(7):1981-93. doi: 10.1890/07-0630.1.
Optimal foraging theory predicts that individuals should become more opportunistic when intraspecific competition is high and preferred resources are scarce. This density-dependent diet shift should result in increased diet breadth for individuals as they add previously unused prey to their repertoire. As a result, the niche breadth of the population as a whole should increase. In a recent study, R. Svanbäck and D. I. Bolnick confirmed that intraspecific competition led to increased population diet breadth in threespine stickleback (Gasterosteus aculeatus). However, individual diet breadth did not expand as resource levels declined. Here, we present a new method based on complex network theory that moves beyond a simple measure of diet breadth, and we use the method to reexamine the stickleback experiment. This method reveals that the population as a whole added new types of prey as stickleback density was increased. However, whereas foraging theory predicts that niche expansion is achieved by individuals accepting new prey in addition to previously preferred prey, we found that a subset of individuals ceased to use their previously preferred prey, even though other members of their population continued to specialize on the original prey types. As a result, populations were subdivided into groups of ecologically similar individuals, with diet variation among groups reflecting phenotype-dependent changes in foraging behavior as prey density declined. These results are consistent with foraging theory if we assume that quantitative trait variation among consumers affects prey preferences, and if cognitive constraints prevent individuals from continuing to use their formerly preferred prey while adding new prey.
最优觅食理论预测，当种内竞争激烈且偏好资源稀缺时，个体应变得更加机会主义。这种密度依赖的饮食转变应导致个体的饮食广度增加，因为它们将以前未使用的猎物纳入其食谱。结果，整个种群的生态位宽度应该会增加。在最近的一项研究中，R. 斯万贝克和D. I. 博尔尼克证实，种内竞争导致三刺鱼（Gasterosteus aculeatus）种群的饮食广度增加。然而，随着资源水平下降，个体的饮食广度并未扩大。在这里，我们提出一种基于复杂网络理论的新方法，该方法超越了简单的饮食广度测量，并用该方法重新审视了三刺鱼实验。该方法表明，随着三刺鱼密度增加，整个种群增加了新的猎物类型。然而，尽管觅食理论预测生态位扩展是通过个体除了以前偏好的猎物之外还接受新猎物来实现的，但我们发现，即使种群中的其他成员继续专门捕食原来的猎物类型，一部分个体也不再使用它们以前偏好的猎物。结果，种群被细分为生态上相似的个体组，随着猎物密度下降，组间的饮食差异反映了觅食行为中依赖表型的变化。如果我们假设消费者之间的数量性状变异会影响猎物偏好，并且认知限制阻止个体在添加新猎物的同时继续使用其以前偏好的猎物，那么这些结果与觅食理论是一致的。
