On the Evolution of Geographic Range
Friday seminar by Michael Foote.
Geographic ranges of species are highly dynamic on both ecological and geological time scales. Rapid changes are observed in ecological time, and ranges also expand and contract, often rather symmetrically, over millions of years. Biotic interactions and tracking of the physical environment have both been suggested as possible explanations for the regular long-term pattern. Here we test a third possibility, that the regular waxing and waning is the outcome of a random walk in which species experience random increases and decreases in their ranges throughout their durations. We find that observed range histories of Cenozoic molluscs of New Zealand are inconsistent with random walks; they are far more volatile, and there is a significant tendency for ranges to increase when they are narrow and to decrease when they are wide. This suggests that some factors are driving geographic range actively up and down. Identifying these factors is an important challenge for future work.
Department of the Geophysical Sciences, The University of Chicago