Data from: The evolution of foraging rate across local and geographic gradients in predation risk and competition

Multiple theories predict the evolution of foraging rates in response to environmental variation in predation risk, intraspecific competition, time constraints, and temperature. We tested six hypotheses for the evolution of foraging rate in 24 spotted salamander (Ambystoma maculatum) populations from three latitudinally divergent sites using structural equation models derived from theory and applied to our system. We raised salamander larvae in a common-garden experiment and then assayed foraging rate under controlled conditions. Gape-limited predation risk from marbled salamanders solely explained foraging rate variation among populations at the southern site, which was dominated by this form of selection. However, at the middle and northern sites, populations evolved different foraging rates depending on their unique responses to local intraspecific density. The coupling of gape-limited predation risk from marbled salamanders and high intraspecific density at the middle site jointly contributed to selection for rapid foraging rate. At the northernmost site, intraspecific density alone explained 97% of the interpopulation variation in foraging rate. These results suggest that foraging rate has evolved multiple times in response to varying contributions from predation risk and intraspecific competition. Predation risk often varies along environmental gradients, and, thus, organisms might often shift evolutionary responses from minimizing predation risk to maximizing intraspecific competitive performance.多项生态学理论预测，觅食速率的演化会响应捕食风险、种内竞争（intraspecific competition）、时间限制与温度等环境因子的变化。本研究采用基于理论推导、适配本研究体系的结构方程模型（structural equation models），对来自3个纬度梯度样地的24个斑点钝口螈（spotted salamander, *Ambystoma maculatum*）种群的觅食速率演化相关的6个假说开展了检验。我们通过同质园实验（common-garden experiment）培育钝口螈幼体，随后在可控实验条件下测定其觅食速率。在南部样地，大理石钝口螈（marbled salamanders）引发的体型限制型捕食风险（gape-limited predation risk）可单独解释种群间的觅食速率差异，该样地的选择压力主要由这类捕食风险主导。但在中部与北部样地，种群的觅食速率演化差异则取决于其对本地种内密度的独特响应模式。中部样地中，大理石钝口螈带来的体型限制型捕食风险与高种内密度的共同作用，共同驱动了针对快速觅食速率的选择。在最北部的样地，种内密度仅可解释97%的种群间觅食速率差异。上述结果表明，觅食速率曾多次演化，以响应捕食风险与种内竞争的差异化贡献强度。捕食风险通常会沿环境梯度发生动态变化，因此生物的演化响应往往会从最小化捕食风险转向最大化种内竞争表现。