Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire 03755, USA.
Nature. 2010 Jun 3;465(7298):613-6. doi: 10.1038/nature09020. Epub 2010 May 9.
Field experiments that measure natural selection in response to manipulations of the selective regime are extremely rare, even in systems where the ecological basis of adaptation has been studied extensively. The adaptive radiation of Caribbean Anolis lizards has been studied for decades, 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 hypothesis that intraspecific competition is more important than predation in shaping the selective landscape for traits central to the adaptive radiation of Anolis ecomorphs.
野外实验可以测量自然选择对选择机制的响应，但即使在适应的生态基础已被广泛研究的系统中，这种实验也极为罕见。加勒比海鬣蜥的适应性辐射已经研究了几十年，这为在野外选择替代因素的影响提供了精确的预测。在这里，我们提供了实验证据，证明了两种假定的选择因素在塑造经典岛屿辐射的适应性景观方面的相对重要性。我们操纵了棕色鬣蜥（Anolis sagrei）的全岛种群，以衡量捕食和竞争作为自然选择因素的相对重要性。我们在 6 个岛屿上排除或包括鸟类和蛇类捕食者，这些岛屿的蜥蜴种群密度从低到高不等，然后测量每个种群随后在行为和自然选择方面的差异。捕食者改变了蜥蜴的栖息行为并增加了死亡率，但捕食处理并没有改变表型特征的选择。相比之下，实验性地增加种群密度显著增加了有利于体型大、相对肢体长度长和高跑步耐力的生存力选择的强度。我们在 A. sagrei 中的结果与以下假设一致，即种内竞争比捕食在塑造对适应辐射至关重要的特征的选择景观方面更为重要。
