Dissertation Research: Geographic Range Limits of Monkeyflowers (Mimulus): Testing the Roles of Gene flow, Trade-offs and Population Dynamics

Michigan State University, East Lansing MI

Investigators

Abstract

Every species survives and reproduces in a limited geographic area. Although distribution limits are universal, little is known about the evolutionary constraints that hinder range expansion. This study will examine range limits of monkey-flowers (Mimulus lewisii and M. cardinalis) across their elevation ranges in California's Sierra Nevada Mountains. Project goals are to identify life stages, traits, and environmental factors that decrease survival and reproduction at range limits and to conduct empirical tests of models of range limits. Range boundaries may arise because matings between central and edge populations create offspring unfit for the edge environment. To test this model, the survival and reproduction of central-edge versus edge-edge offspring will be compared in the edge environment. Alternatively, correlations among traits may constrain the direction of adaptation, creating range limits where a set of traits appropriate for the edge environment is not produced. This model will be tested by comparing optimum trait values at the range limit to species' actual trait values. The origin and maintenance of geographic range limits are evolutionary riddles first discussed by Darwin, yet 150 years later experimental data are limited. Range limits are also a topic of importance to conservationists because species' distributions are forecasted to shift towards the poles and to higher elevations in response to global climate change. However, without knowledge of the processes operating at range boundaries, accurate predictions about the magnitude of such distribution shifts are difficult.