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351 16 THE FIVE FAUNAS RECONSIDERED The Anolis evolutionary pageant exhibits a fundamental duality. On one hand, the Greater Antillean ecomorphs are renowned for convergence of entire communities, with the same set of ecomorphs evolving repeatedly. On the other hand, only one of the other four anole faunas—the anoles of the small islands of the Greater Antilles— contains many types of ecomorphs. The story of three of the other anole faunas—the mainland, the Lesser Antilles, and the unique anoles of the Greater Antilles—is primarily one of non-convergence, both internally and with the ecomorph radiations. The simplest explanation for this contrast is that the environments in the Greater Antilles select for the same set of phenotypes, whereas the environments in the other localities select for different phenotypes. By environments, I mean abiotic factors such as temperature and humidity, as well as the structures which anoles use, the food they eat, and the other species with which they interact as predators, prey, and competitors. This idea can be cast in the framework of an adaptive landscape in which the x- and y-axes represent different aspects of the phenotype and the height of the z-axis represents the extent to which multivariate phenotypes are favored by selection (reviewed in Fear and Price, 1998; Schluter, 2000; Arnold et al., 2001). In this light, the simple hypothesis above would suggest that adaptive peaks are in the same place in the Greater Antilles, and in different places in the other areas (Fig. 16.1).421 421. Keep in mind the abstract nature of figures like 16.1. Although the adaptive landscape for a single population in a static environment is mathematically defined and analytically tractable, the extension to consideration of the landscape for multiple co-occurring species in an evolving clade should be viewed as a heuristic analogy. Technically, the adaptive landscape specifically refers to how a population will evolve in a losos_ch16.qxd 4/11/09 9:38 AM Page 351 This hypothesis makes a major assumption, that evolution is completely predictable; that is, movement through phenotype space is unhindered such that species will always evolve to the highest available peak (assuming, in addition, that once a peak is occupied by one species, it cannot then be occupied evolutionarily by another species). In addition , as an explanation of ecomorph convergence, the hypothesis also assumes a unitary match between the environmental factors that impose selection and the possible phenotypic responses—that is, that only one phenotypic solution exists for problems posed by the environment.422 These assumptions need not be true, and if they are not, then the simple hypothesis above may be incorrect: convergent evolutionary radiations may not necessarily imply similarity in environments, and lack of convergence in radiations may occur even in very similar environments. 352 • T H E F I V E F A U N A S R E C O N S I D E R E D Cuba Hispaniola Mainland Fitness Phenotype I Phenotype II F I G U R E 16.1 Similar adaptive landscapes on the islands of the Greater Antilles (represented here by Cuba and Hispaniola) may be responsible for the evolution of the same set of ecomorphs on each island, whereas a different landscape on the mainland could account for the different patterns of morphological evolution found there. particular selective setting, and multiple peaks on that landscape indicate different regions of phenotypic space favored by selection. However, the existence of multiple peaks for a single population does not necessarily imply that multiple, sympatric species in that environment would evolve to the different peaks. Rather, the landscapes for each of the species would not necessarily be the same, because each species would occur with a different complement of co-occurring species (i.e., each species is part of the environment for other species). Consequently, to envision whether the same set of phenotypes would be favored on different islands, we would need to look at the landscapes for each species separately. However, these landscapes might not be static, but rather might change each time a new species joins the community. In addition, as a species evolves, then so might the adaptive landscapes for all co-occurring species. None of these issues is incorporated into the mathematical underpinning of the adaptive landscape. Consequently, application of this concept to an evolving adaptive radiation should be considered a metaphor, albeit an extremely useful one. 422. This view of selection—the environment creating problems to which populations...

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