Grasshopper Food Web Analysis: Use of Carbon Isotope Ratios to Examine Feeding Relationships Among Terrestrial Herbivores

Abstract

Twenty-five species of grasshoppers and 61 plant species were collected from a west Texas study site. Stomach contents of grasshoppers and carbon isotope ratios for plants and grass- hoppers were determined and correlated to test the hypothesis that herbivores have the same carbon isotope ratio as their food. The results of this study include: (1) grasshopper carbon isotope ratios were similar to the carbon isotope ratios of the diet; (2) d d and Y Y of the same species differed little in their feeding on CQ and C4 plants as measured either by stomach content data or carbon isotope ratios; (3) in 7 specialist species which fed on either C3 or C4 plants, individual grasshoppers generally differed in their carbon isotope ratios by 1.6%. or less, 3 generalist species which fed on substantial amounts of both C3 and C4 plants showed larger amounts of individual variation; (4) both the average carbon isotope ratio for a grasshopper species and the variability of carbon isotope ratios among individuals of the species are useful in predicting grasshopper diet in terms of mixtures of Ci and C4 plants.