1. Department of Mathematics and Computer Science, Rhodes College , Memphis, TN 38112 , USA
2. Department of Biology, University of Virginia , Charlottesville, VA 22904 , USA
3. Department of Mathematics and Statistics, Valparaiso University , Valparaiso, IN 46383 , USA
4. Department of Organismal Biology and Ecology, Colorado College , Colorado Springs, CO 80903 , USA