John P. Bryant Rongsong Liu Stephen A. Gourley Charles J Krebs Paul B Reichardt Donald L. DeAngelis 2015 <p>A necessary condition for a snowshoe hare population to cycle is reduced reproduction after the population declines. But the cause of a cyclic snowshoe hare population's reduced reproduction during the low phase of the cycle, when predator density collapses, is not completely understood. We propose that moderate-severe browsing by snowshoe hares upon preferred winter-foods could increase the toxicity of some of the hare's best winter-foods during the following hare low, with the result being a decline in hare nutrition that could reduce hare reproduction. We used a combination of modeling and experiments to explore this hypothesis. Using the shrub birch <i>Betula glandulosa</i> as the plant of interest, the model predicted that browsing by hares during a hare cycle peak, by increasing the toxicity <i>B. glandulosa</i> twigs during the following hare low, could cause a hare population to cycle. The model's assumptions were verified with assays of dammarane triterpenes in segments of <i>B. glandulosa</i> twigs and captive hare feeding experiments conducted in Alaska during February and March 1986. The model's predictions were tested with estimates of hare density and measurements of <i>B. glandulosa</i> twig growth made at Kluane, Yukon from 1988&ndash;2008. The empirical tests supported the model's predictions. Thus, we have concluded that a browsing-caused increase in twig toxicity that occurs during the hare cycle's low phase could reduce hare reproduction during the low phase of the hare cycle.</p> application/pdf 10.1111/oik.01671 en Wiley A plant toxin mediated mechanism for the lag in snowshoe hare population recovery following cyclic declines article