Acknowledgements
I wish to thank Ben Gilbert and Art Weis for advice and financial support, and the staff and students of the Koffler Scientific Reserve for their assistance. Stephen De Lisle and Colin Bonner were key collaborators and sounding boards when beginning this work. I was variously supported by Sigma Xi, NSERC, OGS, the University of Toronto, and the Center for Population Biology (UC Davis) while collecting data and writing this manuscript.