Understanding coexistence within community modules such as intraguild predation (IGP), where an omnivore both preys on and competes with an intermediate consumer for a shared resource, has provided insight into the mechanisms that promote the persistence of complex food webs. Adaptive, predator-specific defense has been shown theoretically to enhance coexistence of IGP communities when employed by shared prey. Yet to date, all such theory has assumed that prey have an accurate perception of predation risk and appropriate antipredator responses, assumptions that may not be justified when considering a novel predator. We therefore consider the effects of an introduced predator on IGP coexistence, describing two invasion scenarios: suboptimal defense, whereby a similar invader elicits an ineffective antipredator response; and naïveté toward an unfamiliar invader, for which prey fail to accurately estimate predation risk. We examine predictions for native predator persistence across gradients of enrichment and defense costs. The model predicts that predator novelty can weaken the effect of adaptive defense, causing exclusion of native predators that would persist in the absence of novelty and inducing unstable dynamics in previously stable regions of parameter space. Coexistence is predicted to be more sensitive to the effects of suboptimal defense than to naïveté, and differentially leads to the exclusion of native predators in highly productive environments and when defense costs are low. Moderate novelty of the omnivore can increase resource density via a trophic cascade, while consumer novelty can either lead to omnivore exclusion or facilitate three-species coexistence by providing a subsidy to the otherwise excluded native omnivore. Our analyses suggest that models of adaptive defense are sensitive to assumptions regarding predator–prey eco-evolutionary experience and that predator novelty has significant implications for food web dynamics.

了解群落模块内的共存，例如公会内捕食（IGP），杂食动物既捕食中间消费者，又与中间消费者竞争共享资源，有助于深入了解促进复杂食物网持久存在的机制。理论上，适应性、针对捕食者的防御已被证明可以在共享猎物时增强 IGP 群落的共存。然而迄今为止，所有这些理论都假设猎物对捕食风险有准确的感知和适当的反捕食者反应，但在考虑新的捕食者时，这些假设可能不合理。因此，我们考虑引入的捕食者对 IGP 共存的影响，描述两种入侵场景：次优防御，类似的入侵者引发无效的反捕食者反应；对不熟悉的入侵者表现出天真，猎物无法准确估计被捕食的风险。我们研究了对本地捕食者在丰富度和防御成本梯度上的持久性的预测。该模型预测，捕食者的新颖性会削弱适应性防御的效果，导致在没有新颖性的情况下持续存在的本地捕食者被排除在外，并在参数空间的先前稳定区域中诱发不稳定的动态。据预测，共存对次优防御的影响比对天真的影响更敏感，并且在高生产力环境和防御成本较低时会不同程度地导致本地捕食者被排除在外。杂食动物的适度新颖性可以通过营养级联增加资源密度，而消费者的新颖性可以导致杂食动物排斥，或者通过向原本被排斥的本地杂食动物提供补贴来促进三个物种共存。我们的分析表明，适应性防御模型对捕食者-被捕食者生态进化经验的假设很敏感，并且捕食者的新颖性对食物网动态具有重大影响。