Dietary Asymmetry in Leaf Litter Frogs and Lizards in a Transitional Northern Amazonian Rain Forest

Abstract

The use of food resources by two arthropodivorous groups of leaf litter vertebrates, frogs and lizards, was studied in a transitional tropical lowland forest in Roraima, Brazil. Nine species of frogs, represented primarily by small-bodied juveniles, and seven species of lizards, primarily small-bodied adults, composed the leaf litter fauna at the end of the wet season when the study was performed. Eighty-two prey categories, identified to family level, were recognized in the diets of these species of frogs and lizards. Overlaps in diet indicated little similarity among most species in prey types eaten, although a well-defined termite-ant guild composed of two species was identified. Ants, insect larvae, beetles, and termites contributed most to diets of all species combined, but frogs typically consumed more ants than lizards. As a group, frogs ate smaller prey than lizards, even when prey sizes were adjusted for body size. Frogs in general contained more prey than lizards (21.7 items per frog compared to 6.7 items per lizard) and had significantly larger stomach content volumes than lizards, indicating a major divergence in the basic strategy of food gathering between frogs and lizards. Frogs may have evolved relatively larger gut storage capacity to offset extended food shortages associated with prolonged inactivity during drought. However, differences in consumption of ants by frogs and lizards may relate to differences in defense strategies between the two groups. All amphibians have integumentary granular glands, which secrete many different compounds used in defense. Ants produce a variety of toxins, and some evidence in one lineage of frogs suggests that frogs may incorporate toxins into their skin from insects in their diets. Future work may elucidate whether lizard dietary choice has evolved to optimize energy intake whereas frog dietary choice has evolved to optimize uptake of chemicals important for defense.