Lawler S P, Morin P J
Am Nat. 1993 May;141(5):675-86. doi: 10.1086/285499.
In theory, food chain length and omnivory are pivotal elements of food web structure that can affect the population dynamics of species within the web. Long food chains are thought to be less stable than shorter food chains, and omnivores are thought to destabilize food webs, although populations of omnivores may be more stable than populations of nonomnivores. In three of four simple food webs assembled from bacteria and protists in laboratory microcosms, the abundance of bacterivorous protists varied more over time when the species occurred in longer versus shorter food chains. The abundance of protists attacked by omnivorous top predators was either more or less temporally variable than in webs where top predators fed only at one adjacent trophic level, depending on the particular combination of interacting species. The abundance of omnivorous top predators varied less over time than the abundance of top predators restricted to feeding only at an adjacent trophic level. Observations of increased temporal variation in prey abundance in longer food chains and low temporal variation in omnivore abundance agree broadly with several predictions of food web theory. The observation that different species in similar trophic positions can exhibit very different dynamics suggests that stability may depend on complex interactions between species-specific life-history traits and general patterns of food web architecture.
从理论上讲，食物链长度和杂食性是食物网结构的关键要素，会影响食物网内物种的种群动态。人们认为长食物链不如短食物链稳定，杂食动物会破坏食物网的稳定性，尽管杂食动物种群可能比非杂食动物种群更稳定。在实验室微观环境中由细菌和原生生物组成的四个简单食物网中的三个里，当物种处于较长而非较短食物链时，食细菌原生生物的丰度随时间变化更大。被杂食性顶级捕食者捕食的原生生物的丰度，与顶级捕食者仅在相邻营养级觅食的食物网相比，在时间上的变化要么更大要么更小，这取决于相互作用物种的特定组合。杂食性顶级捕食者的丰度随时间的变化比仅限于在相邻营养级觅食的顶级捕食者的丰度变化更小。关于较长食物链中猎物丰度的时间变化增加以及杂食动物丰度的时间变化较小的观察结果，与食物网理论的几个预测大致相符。处于相似营养级的不同物种可能表现出非常不同的动态这一观察结果表明，稳定性可能取决于物种特定生活史特征与食物网结构一般模式之间的复杂相互作用。
