Competition Between Insectivorous Lizards and Birds in Central Panama

Abstract

The following evidence suggests that birds and lizards compete for their arthropod prey on islands in Lake Gatun, Panama: (1) there is extensive overlap between the diets of a representative bird and lizard, (2) at least one insectivorous lizard, Anolis limifrons , appears to be food-limited, (3) birds appear to have a major impact on arthropod abundances, (4) avian abundance is negatively correlated with the physiological condition and, thus, with the fecundity of female A. limifrons , (5) bird and lizard population densities are negatively correlated. Lake Gatun was formed in 1914. In the intervening years, a great many bird species have been lost from the smaller islands, but very few lizard populations have gone extinct. Ninety-six percent of the between-site variation in avian abundances is accounted for by the number of bird species present at a site. Sites with depauperate avifaunas are characterized by low avian abundances because the species present do not experience ecological release, and resources which are utilized by birds on species-rich sites are not exploited by birds on species-poor sites. Thus, avian abundances are controlled by factors extrinsic to the bird-lizard interaction, and lizards opportunistically increase their abundances at sites with low avian abundances.