Consequence of Inter Class Competition and Predation on the Adaptive Radiation of Lizards and Birds in the Dry Forest of Western Madagascar

Abstract

Species interactions among phylogenetically distant but ecologically re- lated vertebrates were studied in a dry forest of western Madagascar to evaluate whether competition and predation between lizards and birds have reciprocally af- fected adaptive radiation in Madagascar. Of 49 terrestrial and diurnal birds regularly seen in the study forest, we identified six guilds as carnivore (5 spp.), omnivore (2 spp.), carnivore/insectivore (7 spp.), strict insectivore (15 spp.), insectivore/nectari- vore (6 spp.), and frugivore (5 spp.). Twelve lizards species were classified as omni- vore (1 sp.), strict insectivore (9 spp.), and insectivore with occasional frugivory and nectarivory (2 spp.). The most dominant guilds of the vertebrates in terms of biomass were folivorous/frugivorous parrots, doves, and lemurs (6.7 kg/ha), followed by in- sectivorous lizards (1.7 kg/ha) and insectivorous birds (0.8 kg/ha) in the Ampijoroa dry forest. Despite their lower biomass, insectivorous birds appeared to be competi- tively more advantageous than the lizards in terms of prey consumption speed (230 prey/ha/hr by birds vs. 35 prey/ha/hr by lizards). Insectivorous and carnivorous birds may have kept insectivorous lizards from radiating in various niches in Madagascar, and may have promoted a reclusive lifestyle in lizards.