Centre for Ecological and Evolutionary Synthesis, Department of Biology, University of Oslo, Blindern, N-0316 Oslo, Norway.
Am Nat. 2011 Sep;178(3):397-410. doi: 10.1086/661250.
Phenotypically plastic traits can be expressed as continuous reaction norms or as threshold traits, but little is known about the selective conditions that favor one over the other. We study this question using a model of prey defenses in which prey can induce any level of defense conditional on cues that are informative of local predator density. The model incorporates a trade-off between defense expression and fecundity and feedback between the defense level of prey and predator attack rates. Both continuous reaction norms and threshold traits can emerge as evolutionarily stable solutions of defense induction, and we show that the shape of the trade-off curve plays a key role in determining the outcome. Threshold traits are favored when selection is disruptive. Ecological conditions that favor defense dimorphisms in the absence of cues will favor threshold traits in the presence of slightly informative cues. We caution that continuous reaction norms and threshold traits may result in similar patterns of defense expression at the population level, and we discuss potential pitfalls of inferring reaction norm type from observational data.
表型可塑性特征可以表现为连续反应规范或阈值特征，但对于哪种特征更有利于选择的条件知之甚少。我们使用一种猎物防御模型来研究这个问题，在该模型中，猎物可以根据提示信息（提示信息可以提供当地捕食者密度的信息）来诱导任何程度的防御。该模型包含防御表达和繁殖力之间的权衡以及猎物防御水平和捕食者攻击率之间的反馈。连续反应规范和阈值特征都可以作为防御诱导的进化稳定解决方案出现，我们表明，权衡曲线的形状在确定结果方面起着关键作用。当选择具有破坏性时，阈值特征更受青睐。在没有提示信息的情况下有利于防御二态性的生态条件，在提示信息略有信息的情况下有利于阈值特征。我们警告说，在种群水平上，连续反应规范和阈值特征可能会导致相似的防御表达模式，我们还讨论了从观测数据推断反应规范类型的潜在陷阱。
