Comparison of herbivore damage to Ammophila breviligulata and plant nitrogen content on the Sturgeon Bay dunes along Lake Michigan

Abstract

The dunes along Lake Michigan are especially nitrogen poor, and this presents a problem for all organisms that live there. Both plants and herbivores have aquired adaptations that help them obtain adequate amounts of nitrogen. The purpose of this study was to examine the amount of nitrogen in Ammophila breviligulata and its relationship to insect herbivory. A. breviligulata plants were collected at different distances from the shore and their nitrogen content and amount of herbivory were measured. Herbivory did not vary significantly with either distance from the shore (p = 0.569) or plant nitrogen content (p = 0.894). However nitrogen content did increase in A. breviligulata as the distance of the plant from the shore increased (p = 0.037) despite a decrease in the occurrence of A. breviligulata farther from the shore (p < 0.01). Increased nitrogen content of A. breviligulata at greater distances from the shore was consistent with previous results and with expected results based on patterns of primary succession on the dunes. Herbivory may not have shown significant variation with distance from the shore because the sample size was too small or the costs of travel to further plants did not allow optimal foraging.