Neotropical Plant Dynamics During the Cenozoic-Diversification, and the Ordering of Evolutionary and Speciation Processes

Abstract

Previous paleobotanical studies on Tertiary floras from northern Latin America have docu- mented that the lowland tropical rain forest and associated communities underwent significant change in their range and composition during the past 60 Ma. New data from pollen and spore assemblages allow refinement in the nature of these changes in three different geographic regions of the neotropics. At the northern limit in central Mexico through northern Central America, changing climates, particularly fluctuat- ing temperatures, are revealed as a principal force driving vegetation dynamics. In southern Central America (including the proto-Antilles), climatic change had less effect on the vegetation. Rather, there was extensive volcanism and profound, rapid alterations in physiography. In the Amazon Basin there were limited topographic changes and moderate climatic effects. A primary forcing mechanism was fluctuating water tables induced by sea-level changes. It is speculated that these separate histories may have elicited a reordering in the myriad of factors constituting the speciation process and, therefore, provided different mechanisms for achieving biodiversity. An awareness of these separate physiographic provinces with distinct environmental histories may be useful in 1) accounting for geographically correlated genotypic and phenotypic features within a genus; 2) understanding factors that shaped the origin and diversification of individual taxa, and 3) refining scenarios to explain diversity in various parts of the neotropics.