Contributions of C3 and C4 plants to higher trophic levels in an Amazonian savanna

We studied the energy flow from C-3 and C-4 plants to higher trophic levels in a central Amazonian savanna by comparing the carbon stable-isotope ratios of potential food plants to the isotope ratios of species of different consumer groups. All C-4 plants encountered in our study area were grasses and all C-3 plants were bushes, shrubs or vines. Differences in delta(13)C ratios among bushes ((x) over bar = -30.8, SD = 1.2), vines ((x) over bar = -30.7, SD = 0.46) and trees ((x) over bar = -29.7, SD = 1.5) were small. However the mean delta(13)C ratio of dicotyledonous plants((x) over bar = -30.4, SD = 1.3) was much more negative than that of the most common grasses ((x) over bar = -13.4, SD = 0.27). The insect primary consumers had delta(13)C ratios which ranged from a mean of -29.5 (SD = 0.37) for the grasshopper Tropidacris collaris to a mean of -14.7 (SD = 0.56) for a termite (Nasuti-termes sp.), a range similar to that of the vegetation. However, the common insectivorous and omnivorous vertebrates had intermediate values for delta(13)C, indicating that carbon from different autotrophic sources mixes rapidly as it moves up the food chain. Despite this mixing, the frogs and lizards generally had higher Values of delta(13)C ((x) over bar = -21.7, SD = 1.6; (x) over bar = -21.9, SD = 1.8, respectively) than the birds ((x) over bar = -24.8, SD = 1.8) and the only species of mammal resident in the savanna ((x) over bar = -25.4), indicating that they are generally more dependent on, or more able to utilise, food chains based on C-4 grasses.