A phylogenetic analysis of character displacement in Caribbean Anolis lizards

Twenty-seven islands in the Lesser Antilles contain either 1 or 2 species of Anolis lizards. On 9 of the 10 2-species islands, the species differ substantially in size; 16 of the 17 one-species islands harbor an intermediate-sized species. Two processes could produce such a pattern: size adjustment (or character displacement), in which similar-sized species evolve in different directions in sympatry; and size assortment, in which only different-sized species can successfully colonize the same island together. Size evolution appears rare (a minimum of 4-7 instances of substantial size evolution). In the northern (but not the southern) Lesser Antilles, size change was significantly greater when a descendant taxon occurred on a 2-species island and its hypothetical ancestor occurred on a 1-species island, supporting the size adjustment hypothesis, though size adjustment might have occurred only once. The relative rarity of size evolution suggests that size assortment might be responsible for non-random patterns. Similar-sized species might not coexist because they interbreed and coalesce into one gene pool. Competitive exclusion is probably responsible for the pattern of size assortment in the N Lesser Antilles; both competitive exclusion and interbreeding of closely related species of similar size might be responsible for the patterns evident in the S Lesser Antilles. -from Author