Foraging trait variation in Ambystoma maculatum

Predator-prey interactions often vary markedly across natural landscapes. One explanation for this variation is local genetic differentiation of prey traits due to selection from predators. Here, I evaluated the relative contributions of selection from a gape-limited predator (Ambystoma opacum) and spatial location within a larger landscape to explanations of variation in foraging, growth, and survival in 10 populations of temporary pond breeding salamander larvae (Ambystoma maculatum). In parameterized models, high gape-limited predation risk was predicted to select for intense foraging and rapid growth in larvae when migration rates were low (less than 5%). Under common garden conditions, salamander larvae from populations naturally exposed to constant predation risk from A. opacum foraged more actively than those from populations faced with lower predation risks. Higher foraging rates were associated with lower survival in populations exposed to free-ranging A. opacum predators. These results demonstrate for the first time that prey hunger can evolve in a natural landscape of variable gape-limited predation risk depending on natural selection for growth into a size refuge. Moreover, evidence suggests that foraging-predation risk tradeoffs can evolve over microgeographic scales. However, foraging rates also appear to have been affected by gene flow: prey individuals from populations with high predation risk foraged more actively if located within regions with similar predation threats. This interaction between local selection and spatial location suggests a joint role for adaptation and maladaptation in shaping species interactions across natural landscapes, a finding with implications for dynamics at the population, community, and metacommunity levels.捕食者-猎物相互作用在自然景观中往往存在显著差异。针对这一差异的一种解释是，猎物性状会因捕食者的选择压力而发生局部分化。本研究评估了口限捕食者（gape-limited predator，大理石钝口螈Ambystoma opacum）的选择压力与大尺度景观内的空间位置，对10个临时性池塘繁殖的斑点钝口螈（Ambystoma maculatum）幼体的觅食、生长与存活差异的相对贡献。在参数化模型中，当迁移率低于5%时，高口限捕食风险会通过自然选择促使幼体演化出高强度觅食与快速生长的策略。在同质园common garden实验条件下，天然暴露于大理石钝口螈持续捕食风险的种群的幼体，其觅食活跃度高于来自低捕食风险种群的幼体。在暴露于自由活动的大理石钝口螈捕食者的种群中，更高的觅食速率与更低的存活率呈负相关。本研究首次证实，在口限捕食风险可变的自然景观中，猎物的饥饿相关性状可发生演化，这一演化取决于针对生长至体型避难所的自然选择。此外，证据表明觅食-捕食风险权衡（foraging-predation risk tradeoffs）可在微地理尺度上发生演化。然而，觅食速率似乎也受到基因流的影响：来自高捕食风险种群的猎物个体，若所处区域具有相似的捕食威胁，其觅食活跃度会更高。局域选择与空间位置之间的这种相互作用表明，适应与适应不良共同塑造了自然景观中的物种相互作用，这一发现对种群、群落以及集合群落（metacommunity）层面的动态研究具有重要启示意义。