Range expansions are central to two ecological issues reshaping patterns of global biodiversity: biological invasions and climate change. Traditional theory considers range expansion as the outcome of the demographic processes of birth, death and dispersal, while ignoring the evolutionary implications of such processes. Recent research suggests evolution could also play a critical role in determining expansion speed but controlled experiments are lacking. Here we use flour beetles (Tribolium castaneum) to show experimentally that mean expansion speed and stochastic variation in speed are both increased by rapid evolution of traits at the expansion edge. We find that higher dispersal ability and lower intrinsic growth rates evolve at the expansion edge compared with spatially nonevolving controls. Furthermore, evolution of these traits is variable, leading to enhanced variance in speed among replicate population expansions. Our results demonstrate that evolutionary processes must be considered alongside demographic ones to better understand and predict range expansions.
Bibliographical noteFunding Information:
National Science Foundation Grants DEB 0949595 to B.A.M. and DEB 0949619 to R.A.H. During this work C.W.-L. was supported by a Graduate Research Fellowship from the National Science Foundation (Grant No. 1144083) and R.A.H. received support from the USDA via the Colorado Agricultural Experiment Station. We thank J. Vidreo, T. Myers, S. Race, N. Richter, F. Janz, M. Gibson, J. Depompolo, K. Ghale, A. Solon, N. Ochwat, T. Turk, M. Duc Le and R. Ghale for assistance with data collection. We thank B. Ochocki, T. Miller, S. Endriss and M. Vahsen for comments on the manuscript and analyses. Publication of this article was partially funded by the University of Colorado Boulder Libraries Open Access Fund.