| Sumario: | The main purpose of this review is to promote discussion on the impact of modern phylogenetic comparative methods has had on several fields of biology. The combining of comparative methods and phyiogenies is used (1) to infer the ancestral States of morphological, ecological and behavioral patterns and to suggest evolutionary patterns of change, (2) to develop hypotheses about the processes of evolutionary change, (3) to test evolutionary association between two or more characters that might suggest coevolutionary processes or evolutionary constraints, and (4) to correct the nonindependence of species data (e.g. statistical problems of interespecific analyses that are not evolutionary in nature). Because of this, the evaluatíon of adaptation hypotheses has changad dramatically in the last two decades. Now, advances in molecular techniques and phylogenetic reconstruction methods allow researchers to evalúate hypotheses of adaptation using a more robust approach, but Darwinian argumentation or experimental approaches are still used to explain correlation over evolutionary time. My interest here is to ernphasize the use of phyiogenies when testing hypotheses of adaptation and evolution, hypotheses of origin and transition of characters, evolutionary association of two or more characters, coevolution, phylogenetic diversification, and the role that phyiogenies and the comparative methods might play on the idantification and conservation of species at risk. For this reason, I revise eight study cases, including the evolution of (1) dioecy among plants with fleshy fruits dispersed by animáis, (2) gregariousness among butterfly larva prometed by aposematic coloration, (3) wing reduction among macrolepidopteran living on stable forests, (4) néctar robbing among bill-serrated hummingbirds, (5) plant chemistry on herbivore host shifts, (6) floral defenses against "aprovechados that rob néctar, (7) nectarivory among hummingbirds and their adaptive radiation, and (8) host generalization among parasitic cowbirds. The first two systems are used mainly to explain some of the methodological problems and the remaining six conform a conceptual revisión of the use of phylogenies for testing hypotheses of adaptation and in biology/evolutionary ecology. Lastiy, I revise how phyiogenies can be used to establish conservation priorities and to identify bilogical processes that might determine different leveis of susceptibility to extinction because of phylogenetic origin
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