Competition Between Insectivorous Lizards and Birds in Central Panama

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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.

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