Nesting Behavior, Migration, and Dispersal of Neotropical Army Ants (Hymenoptera, Formicidae: Ecitoninae)

Abstract

Army ants, keystone predators in tropical forests, collectively hunt prey and are obligately nomadic. Despite a wide geographic and elevational range, the army ant <italic>Eciton burchellii</italic> is sensitive to environmental extremes and avoids entering deforested areas. Bivouac (nest) sites at high elevation were found to be more frequently located in sheltered locations than at low elevations (Chapter 1). High elevation bivouac sites provide abiotic buffering to <italic>E. burchellii</italic> colonies, though the effect declines at the highest elevations. The combination of forest clearing and high elevations may restrict army ant dispersal in Monteverde, Costa Rica. Restricted dispersal may lead to reduced gene flow, which threatens populations with inbreeding depression and local extinction. We compared individual-based pairwise relatedness estimates of reconstructed queen and male genotypes to resistance distances based on land cover and elevation (Chapter 2). Land cover (deforestation), but not high elevation, was found to inhibit dispersal in army ants in Monteverde. Though significant spatial genetic structure was found in males but not queens, dispersal may be weakly male-biased. A temporal replication revealed no spatial pattern of relatedness over time (Chapter 3). This suggests that cumulative colony emigrations over the lifetime of the queen (before reproduction) may contribute to gene flow in this species. Thus forested habitat corridors should be maintained among fragments to allow for <italic>E. burchellii</italic> colony movements and subsequent gene dispersal. Army ants exhibit top-down effects on prey species and support a wide range of associates from mites to birds. Promoting army ant population persistence will maintain this biodiversity in tropical ecosystems.