自然选择的实验验证很少见，因为人们充分了解、足以能对选择目标做出预测的体系几乎没有。
加勒比名为“安乐蜥”的蜥蜴是个例外。几十年的研究产生了对这个类群的选择目标（身体大小、四肢长度）及选择媒介（竞争、捕食）的精确预测。作为对自然选择的一个验证，Ryan Calsbeek 和 Robert Cox在六个加勒比小岛上对“安乐蜥”进行了大规模的种群操纵。
虽然捕食者的存在的确影响蜥蜴行为，但有利于更大体型、更长的腿和更强体力（形成）的是蜥蜴种群不断增长的密度。看来，物种内竞争对于决定这些蜥蜴的演化来说似乎要比捕食更为重要。（生物谷Bioon.com）
生物谷推荐原文出处：
Nature doi:10.1038/nature09020
Experimentally assessing the relative importance of predation and competition as agents of selection
Ryan Calsbeek& Robert M. Cox
Field experiments that measure natural selection in response to manipulations of the selective regime are extremely rare1, even in systems where the ecological basis of adaptation has been studied extensively. The adaptive radiation of Caribbean Anolis lizards has been studied for decades2, 3, 4, 5, leading to precise predictions about the influence of alternative agents of selection in the wild. Here we present experimental evidence for the relative importance of two putative agents of selection in shaping the adaptive landscape for a classic island radiation. We manipulated whole-island populations of the brown anole lizard, Anolis sagrei, to measure the relative importance of predation versus competition as agents of natural selection. We excluded or included bird and snake predators across six islands that ranged from low to high population densities of lizards, then measured subsequent differences in behaviour and natural selection in each population. Predators altered the lizards’ perching behaviour and increased mortality, but predation treatments did not alter selection on phenotypic traits. By contrast, experimentally increasing population density dramatically increased the strength of viability selection favouring large body size, long relative limb length and high running stamina. Our results from A. sagrei are consistent with the hypothesis6 that intraspecific competition is more important than predation in shaping the selective landscape for traits central to the adaptive radiation of Anolis ecomorphs.
