Polygyny in thief ants responds to competition and nest limitation but not food resources

Abstract

Colonies of ants often house multiple queens, and variation in polygyny often tracks environmental conditions. Three hypotheses have been proposed to describe how environmental variation may account for the degree of polygyny: competition, food limitation and nest limitation. Here I evaluate these hypotheses with studies on litter-nesting thief ants (Solenopsis spp.) throughout a lowland tropical rain forest in Costa Rica. In one component, I measured how polygyny varied across a broad environmental gradient demonstrating substantial variation in resources and competition. In a second component, I manipulated the abundance of food, the spatial presentation of food and the availability of nesting space to assess the effects on queen number. The degree of polygyny increased with nest limitation and competition, but there was no indication that colonies produce queens to capitalize on food availability. The increase in queen number in response to the density of competitors suggests that an increase in queen number enhances exploitative abilities.