Department of Integrative Biology, University of Guelph, Guelph, ON, Canada.
J Evol Biol. 2010 Aug;23(8):1613-22. doi: 10.1111/j.1420-9101.2010.02026.x. Epub 2010 May 26.
Empirical estimates of selection gradients caused by predators are common, yet no one has quantified how these estimates vary with predator ontogeny. We used logistic regression to investigate how selection on gastropod shell thickness changed with predator size. Only small and medium purple shore crabs (Hemigrapsus nudus) exerted a linear selection gradient for increased shell-thickness within a single population of the intertidal snail (Littorina subrotundata). The shape of the fitness function for shell thickness was confirmed to be linear for small and medium crabs but was humped for large male crabs, suggesting no directional selection. A second experiment using two prey species to amplify shell thickness differences established that the selection differential on adult snails decreased linearly as crab size increased. We observed differences in size distribution and sex ratios among three natural shore crab populations that may cause spatial and temporal variation in predator-mediated selection on local snail populations.
经验估计由捕食者引起的选择梯度是常见的，但没有人已经量化了这些估计如何随捕食者的个体发育而变化。我们使用逻辑回归来研究腹足纲贝壳厚度的选择如何随捕食者体型的变化而变化。只有小中和大紫滨蟹（Hemigrapsus nudus）在潮间带蜗牛（Littorina subrotundata）的单一种群内对壳厚度的增加表现出线性选择梯度。对于小中和中体型的螃蟹，壳厚度的适合度函数的形状被确认为线性的，但对于大型雄性螃蟹，形状是驼峰形的，这表明没有定向选择。使用两种猎物物种来放大壳厚度差异的第二个实验表明，随着螃蟹体型的增加，对成年蜗牛的选择差异呈线性减少。我们观察到三个自然滨蟹种群在大小分布和性别比例上的差异，这可能导致在当地蜗牛种群中，捕食者介导的选择在空间和时间上发生变化。
