Speciation and Patterns of Species Diversity
One of the striking features of the damselflies in this system is the disparity in species richness between the two lake types. In the Enallagma, 34 species are associated with fish lakes and only four are associated with dragonfly lakes. In collaboration with Jonathan M. Brown, Grinnell College, and Michael L. May, Rutgers University, we have reconstructed the phylogeny of the Enallagma damselflies using DNA sequence data and morphological characters to examine various potential mechanisms for generating this disparity in species richness. Our results suggest that the simplest explanation for this disparity is that Enallagma have only recently invaded the dragonfly lake habitat. Moreover, our data indicate that about half of all the extant species have arisen sometime within the last 250,000 years from two radiating lineages, and most species arose within the last ~15,000 years. All the dragonfly-lake species are members of this young species group. These results suggest that current diversity patterns may be driven as much by macroevolutionary processes shaping speciation and extinction rates as by ecological mechanisms of coexistence.
We are now continuing this work to examine the phylogeography of these two radiations, and the ecological consequences of creating so many species so quickly.
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