My research illuminates new aspects of the ecological and evolutionary controls on spe-cies invasions of new ecosystems and of the consequences of species invasions for their new ecosystems. First, I develop a new modeling framework for analysis of morphological evolution in cases without extensive phylogenetic or fossil information, and I apply that framework to a study of East African cichlids in Lake Tanganyika. Such work provides critical new insight into the evolutionary and ecological processes underlying their fantastic adaptive radiations that have followed their introductions to East African Great Lakes. Second, I lay the foundations for a fresh analysis of the Great American Biotic Inter-change (GABI), in which the formation of the Panamanian Isthmus allowed exchange between the long isolated faunas of North and South America. The middle Miocene fauna of La Venta, Colombia, provides an ideal opportunity for such analysis. I synthesize studies on this fauna with paleoecological and paleobiological studies for closely related taxa from other times and/or locations. Stable isotope analysis of fossil and authigenic minerals indicates mean annual tem-perature of 30-35°C, with high relative humidity (60-70%) and limited seasonality. Further analysis supports a wet and likely forested ecosystem, but not under a closed canopy. Implica-tions for vegetation composition and mammalian behavior and physiology are also explored. Finally, I apply metadata analysis of mammalian autecology to the dynamics of the GA-BI. Today, over half of South American species are of North American descent, but only three terrestrial genera in temperate North America have South American origins. The reasons for this imbalance are unknown, but hypotheses include competitive exclusion, ecological replacement, or intense predation of South American native taxa, as well as insinuation, in which North American immigrants filled adaptive zones that were previously unoccupied by South American native taxa. Data on diet, locomotion, and body mass from literature sources and new calculations de-fine adaptive zones for all known native and immigrant South American taxa, which allows the testing of these hypotheses. Insinuation is by far the dominant mode for immigrant taxa (≥74%), whereas potential cases of competitive replacement are the least common and quite rare (≤5.9%).