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 grasshoppers 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) @M @M and @V @V of the same species differed little in their feeding on C_3 and C_4 plants are measured either by stomach content data or carbon isotope ratios; (3) in 7 specialist species which fed on either C_3 or C_4 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 C_3 and C_4 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 C_3 and C_4 plants.