Latitudinal Gradients in Plant Palatability in Atlantic Coast Salt Marshes

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DEB-0107604 PenningsEcologists have long hypothesized that herbivore pressure is more intense and that plant defenses are better developed towards the tropics than at higher latitudes. Although some indirect evidence supports these ideas, the large geographic scale of the problem has hampered attempts at more direct studies. My recent work in Atlantic coast salt marshes directly demonstrated that southern marsh plants are less palatable to herbivores than are northern plants of the same species. The current project will test the hypothesis that herbivore pressure in these communities is greater at lower than at higher latitudes. Herbivore pressure will be assessed by planting "standard" plants into marshes in each geographic region and observing herbivore damage, and by herbivore counts. A second goal of the project will be to determine whether the plants require cues such as climate or herbivore damage in order to develop latitudinal differences in palatability, or whether these differences are "pre-programmed". These alternatives will be compared by growing plants from both geographic regions side by side in a common greenhouse. By overcoming several of the logistical problems that have plagued past studies, this project will bring a new level of rigor and understanding to the study of latitudinal gradients in plant palatability.