Professor Engstrom is interested in studying phylogenetic patterns of biodiversity and evolutionary mechanisms underlying those patterns. Research focuses on chromosomal evolution, the role of chromosomal change in reproductive isolation and speciation, and the systematics of small mammals, especially rodents and bats. Current studies include (1) chromosomal speciation and biogeography of Nearctic collared lemmings, (2) applicability of Pleistocene refugial models to speciation in Neotropical rodents, and (3) phylogenetic systematics of New World heteromyine and sigmodontine rodents.