| An important new approach for understanding species' biogeography and evolution has been consideration of historical dimensions underlying ecological variation. Theoretical and empirical evidence suggests that ecological niches of species tend to be conservative over evolutionary time. Although in recent years a theoretical framework has been developed for explaining this finding at the microevolutionary level, little has been done to understand the evolutionary patterns of the niche observed above the species level. In this study, I developed a methodology to analyze both micro- and macroevolutionary patterns of ecological niches of species. At the microevolutionary level, analyses of 23 extant mammal species, modeling ecological niches and reciprocally predicting geographic distributions between the Last Glacial Maximum and present, showed high intertemporal predictivity between time periods, suggesting that niche conservatism is widespread, and that ecological niches represent long-term stable constraints on species' geographic distributions. Niche projections to the present for eight mammal taxa that became extinct at the end of the Pleistocene generally increased in area, and thus do not support the hypothesis of niche collapse as a major driving force in their extinction. At the macroevolutionary level, quantitative measurements of ecological niche dimensions of taxa in the context of their phylogenetic and geographic relationships showed that niche conservatism is variable among taxonomic groups. Niche similarities of taxa were, in general, better explained by geographic distance than by phylogenetic relationships; nonetheless, sister species pairs were more similar to one another in their niches than non-sister species pairs, suggesting that niche conservatism breaks down over moderate periods of evolutionary time. Niche conservatism patterns observed across diverse clades of vertebrates suggest that dispersal capacities of taxa play an important role in limiting ecological divergence. |
