COMPETITION AND COEXISTENCE OF LARVAL ANT LIONS

Abstract

What factors permit the coexistence of competing species? In central Oklahoma, the predaceous ant lions Myrmeleon crudelis and M. immaculatus live in dense aggregations at the sheltered bases of cliff ledges. Three larval instars of each species act as predators and competitors of one another. In controlled field experiments, mortality of second and third instars increased with density, although intra- and interspecific effects were indistinguishable. The presence of third-instar larvae did not affect recruitment or survivorship of first-instar larvae. In all experiments, mortality was predictable on the basis of body mass and larval density, but not species identity. Increased food supply shortened development time and increased adult body mass but did not affect mortality. Larvae near the front of the ant lion aggregation grew faster due to greater food availability but suffered greater mortality in the pupal stage. Although food and space were limiting, neither species was excluded because (1) intra- and interspecific effects were similar; (2) third-instar larvae could not suppress the recruitment of first-instar larvae; and (3) recruitment was patchy in time and space. Oviposition behavior and interactions among adult ant lions may also contribute to larval coexistence.