Stephen Gourley has been involved in an ongoing collaboration with Rongsong Liu (University of Wyoming), Donald L. DeAngelis (US Geological Survey and the Department of Biology, University of Miami) and John P. Bryant (Institute of Arctic Biology, University of Alaska) on how certain plants defend themselves against snowshoe hares in northern Canada and Alaska, and on how hares try to counter this defence by their feeding behaviour. Preferred browse species have a small number of long twig segments and defend only the youngest segments near the twig tip. Hares counter this defence by biting off a twig at an older segment, eating only the older segments and rejecting younger, more toxic attached segments. Less preferred foods such as evergreen spruces adopt a different defence strategy. Stephen and his co-authors have written a paper in which all these defence and counter-defence strategies are modelled mathematically. The paper, to appear in the SIAM Journal on Applied Mathematics, is titled “A mathematical model of woody plant chemical defenses and showshoe hare feeding behavior in boreal forests: the effect of age-dependent toxicity of twig segments“. A link to the journal website can be found here. An important outcome of the analysis is that the defensive strategy adopted by preferred browse species has the capacity to cause plant-hare cycles which is interesting because the spectacular population cycle of showshoe hares is one of the most intriguing features of the ecology of the boreal forest, having captured the attention of biologists and historians for over 100 years.