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We studied the effects of lizard size, and availability of C-3 and C-4 plants, on stable carbon-isotope (delta C-13) ratios of lizards in an Amazonian savanna. Availability of C-3 and C-4 plants was estimated from 500-point quadrats in each of 38 plots of 3.75 ha. Ratios of delta C-13 in muscle tissue were used to estimate the contribution:, of C-3- and C-4-based food chains to the diets of four species of lizards: Cnemidophorus lemiscatus, Kentropyx slriata, Ameiva ameiva, and Anolis auratus. The relative contributions of C-3 and C-4 plants to the diets of the lizards were affected by the extent of shrub cover in C. lemniscatus, A. auratus, and possibly in K. striata. However, there was a strong effect of lizard size among and within lizard species. These results are at variance with a previous evaluation of diet overlap among size classes of these species that was based on overlap in prey taxonomic categories. This indicates that species and/or size classes of predators on arthropods may obtain their energy from food chains based on different autotrophic sources. despite high overlap in the taxonomic categories of prey

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