自然選擇的實驗驗證很少見,，因為人們充分了解,、足以能對選擇目標(biāo)做出預(yù)測的體系幾乎沒有。
加勒比名為“安樂蜥”的蜥蜴是個例外,。幾十年的研究產(chǎn)生了對這個類群的選擇目標(biāo)（身體大小,、四肢長度）及選擇媒介（競爭、捕食）的精確預(yù)測,。作為對自然選擇的一個驗證,，Ryan Calsbeek 和 Robert Cox在六個加勒比小島上對“安樂蜥”進(jìn)行了大規(guī)模的種群操縱。
雖然捕食者的存在的確影響蜥蜴行為,，但有利于更大體型,、更長的腿和更強(qiáng)體力（形成）的是蜥蜴種群不斷增長的密度?？磥?，物種內(nèi)競爭對于決定這些蜥蜴的演化來說似乎要比捕食更為重要,。（生物谷Bioon.com）
生物谷推薦原文出處：
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.
