Department of Mathematics & Statistics, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Mathematics & Statistics, Acadia University, Wolfville, Nova Scotia, Canada.|Department of Mathematics & Statistics, Dalhousie University, Halifax, Nova Scotia, Canada.|Department of Mathematics & Statistics, Dalhousie University, Halifax, Nova Scotia, Canada, Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada.