The Nature of Niche Expansion in West Indian Anolis Lizards I: Ecological Consequences of Reduced Competition

Islands have fewer species than mainland areas of similar size, latitude and topographical complexity. Consequently insular species coexist with fewer competitors. Since competitors restrict a species' resource utilization and abundance, one might predict that island populations would have higher densities and broader niches than their mainland counterparts. Recent comparisons of island and mainland bird populations have shown that insular populations undergo a variety of ecological changes consistent with this prediction. These responses to reduced competition are called niche expansion or ecological release (Wilson, 1961) and include increased abundance, habitat expansion, increased diversity of diet and altitudinal shifts (Diamond, 1970; Keast, 1970; MacArthur et al., 1972; Terborgh and Faaborg, 1973). The propensity for species to exploit a broader spectrum of resources in the absence of competitors constitutes some of the best evidence for the importance of competition in vertebrate communities. But the phenomenon of niche expansion also raises a number of questions concerning the niche dynamics of natural populations which have received little attention: How do species adjust their niches? What evolutionary strategies are involved? To what extent is niche expansion an evolutionary or behavioral event? In this paper I analyze the nature of niche expansion in West Indian Anolis lizards with the aim of understanding the ecological consequences of reduced competition and the adaptations