Bonsall Michael B, Holt Robert D
Department of Biological Sciences and Natural Environment Research Council Centre for Population Biology, Imperial College, London, Silwood Park Campus, Ascot, Berkshire SL5 7PY, United Kingdom.
Am Nat. 2003 Dec;162(6):780-95. doi: 10.1086/379203. Epub 2003 Dec 19.
In the absence of other limiting factors, assemblages in which species share a common, effective natural enemy are not expected to persist. Although a variety of mechanisms have been postulated to explain the coexistence of species that share natural enemies, the role of productivity gradients has not been explored in detail. Here, we examine how enrichment can affect the outcome of apparent competition. We develop a structured resource/consumer/natural enemy model in which the prey are exposed to attacks during a vulnerable life phase, the length of which depends on resource availability. With a single prey species, the model exhibits the "paradox of enrichment," with unstable dynamics at high levels of resource productivity. We extend this model to consider two prey species linked by a shared predator, each with their own distinct resource base. We derive invasion and stability conditions and examine how enrichment influences prey species exclusion and coexistence. Contrary to expectations from simpler, prey-dependent models, apparent competition is not necessarily strong at high productivity, and prey species coexistence may thus be more likely in enriched environments. Further, the coexistence of apparent competitors may be facilitated by unstable dynamics. These results contrast with the standard theory that apparent competition in productive environments leads to nonpersistent interactions and that coexistence of multispecies interactions is more likely under equilibrial conditions.
在没有其他限制因素的情况下，物种共享一种常见有效天敌的组合预计无法持续存在。尽管人们提出了多种机制来解释共享天敌的物种的共存现象，但生产力梯度的作用尚未得到详细探讨。在此，我们研究资源富集如何影响似然竞争的结果。我们构建了一个结构化的资源/消费者/天敌模型，其中猎物在脆弱的生命阶段会遭受攻击，该阶段的时长取决于资源可用性。对于单一猎物物种，该模型呈现出“富集悖论”，即在高资源生产力水平下动态不稳定。我们扩展此模型以考虑由共享捕食者连接的两种猎物物种，每种猎物都有其独特的资源基础。我们推导了入侵和稳定性条件，并研究资源富集如何影响猎物物种的排斥和共存。与更简单的、依赖猎物的模型的预期相反，在高生产力水平下，似然竞争不一定强烈，因此在资源富集的环境中猎物物种共存的可能性可能更大。此外，不稳定的动态可能有助于似然竞争者的共存。这些结果与标准理论形成对比，标准理论认为在生产性环境中的似然竞争会导致非持久性相互作用，而多物种相互作用的共存更可能在平衡条件下发生。
