GEOGRAPHIC RANGE, DISPERSAL, AND EVOLUTIONARY SUCCESSION: EVIDENCE FROM LIVING GYMNOSPERMS

The succession of the gymnosperm-dominated Mesozoic flora by the modern angiosperm-dominated flora represents an important transition in evolutionary biology, and has been likened to the succession of Sepkoski's evolutionary faunas. Angiosperms possess numerous traits often interpreted as advantages over gymnosperms, including animal-mediated pollination and dispersal. However, despite the overall late Cretaceous and Cenozoic decline of gymnosperms, some groups of conifers diversified with the angiosperms. Are the Pinaceae and other comparatively successful modern gymnosperm clades thriving in refugia, protected from the diversifying angiosperms, or have they independently acquired some adaptations equivalent to those responsible for the success of angiosperms? Did some gymnosperms once have these traits, but lost them due to extinctions at the end of the Mesozoic?

Geographic range is often cited as one measure of species success and has been related to dispersal mechanism, and many once-prominent gymnosperm genera have seen dramatic range contractions during the Cenozoic (e.g. Ginkgo, Sequoia, Metasequoia). We here study the relationship between geographic range and dispersal mode in living gymnosperms. The Pinaceae, Podocarpaceae, Taxaceae, Juniperus, Gnetum, and Ephedra all exhibit some to substantial biotic dispersal. The Cupressaceae (excluding Juniperus but including Taxodiaceae), Araucariaceae, and some smaller clades are wind dispersed. Extant Ginkgo and cycads do not currently possess effective biotic dispersal, but circumstantial evidence implies that they may have been dispersed by dinosaurs or other reptiles that have since become extinct. Preliminary results using a subset of gymnosperms consisting of cycads, Sciadopitys, and Cupressaceae (including Juniperus) suggest that the three groups possess statistically distinct range patterns; abiotic dispersers are more widespread than cycads, but bird-dispersed Juniperus includes both the most widespread species and several species with more restricted ranges than those of many cycads. If these preliminary results hold, effective dispersal mechanisms are likely instrumental in the successful competition of some gymnosperms with angiosperms. Full results from a dataset comprising all gymnosperms will be discussed.