Interspecific competition is widely considered a powerful process underlying species coexistence and ecological community structure. Although coexistence theory predicts stronger competition between more ecologically similar species, empirical support has largely relied on inferring competition from patterns of species co-occurrence. Coexistence theory also posits that species can only coexist when individuals compete more with conspecifics than with other species, however, few field studies—particularly in reptiles—have simultaneously estimated the strength of both intra- and interspecific competition among co-occurring species. Using an array of 12 experimental plots, we manipulated species presence and population size by plot of three native Anolis lizard species to empirically estimate the strength of competition on one anole species driven by two other species of varying ecological similarity. We observed that the strength of competition—as determined by relative growth rates and gravidity—was highly predictable and correlated to ecological similarity. Interspecific competition was strongest among species of highest ecological similarity, and intraspecific competition—induced by the addition or removal of conspecifics—was consistently the most intense. By employing direct experimental manipulations, our study provides an empirical investigation of the strength of competition as it relates to ecological similarity.

种间竞争被广泛认为是物种共存和生态群落结构的强大过程。尽管共存理论预测生态上更相似的物种之间的竞争会更激烈，但经验支持在很大程度上依赖于从物种共现模式中推断竞争。共存理论还认为，只有当个体与同种的竞争多于与其他物种的竞争时，物种才能共存，然而，很少有实地研究——特别是爬行动物——同时估计了共生物种之间种内和种间竞争的强度。我们利用 12 个实验样地，通过三种本土变色蜥蜴物种的样地来控制物种存在和种群规模，以凭经验估计由两种具有不同生态相似性的其他物种驱动的一种变色蜥物种的竞争强度。我们观察到，竞争的强度（由相对增长率和重力决定）是高度可预测的，并且与生态相似性相关。在生态相似度最高的物种中，种间竞争最为激烈，而由同种的添加或删除引起的种内竞争始终是最激烈的。通过采用直接实验操作，我们的研究提供了与生态相似性相关的竞争强度的实证研究。