Ant assemblage on a coffee farm: spatial mosaic versus shifting patchwork.

Competition has been recognized as a major organizing process in ant communities, with ant communities frequently forming spatial mosaics of dominant species associated with subdominants. Often, species exhibit tradeoffs in their ability to discover versus dominate resources, suggesting a mechanism for coexistence. Here we describe spatial patterns of dominant ants in two sites within a coffee plantation. Ants were sampled for three consecutive years by using tuna baits set on a grid on the ground and on coffee bushes. In addition, so as to determine which species discovered baits first and which species dominated baits, a separate experiment was set up where baits were observed every minute for 2 hr. The relative abundance of species followed a power law, with coefficients of determination ranging from 92 to 97% explanation. At site I the terrestrial community is dominated by two species, Pheidole synanthropica Longino and Pheidole protensa Wilson, whereas at site II the community exhibits codominance of four species: P. synanthropica, P. protensa, Solenopsis geminata F., and Pheidole 1 group. The spatial pattern formed by these species is distinct for each of the sites, both in terms of generalized appearance and dynamic stability. The terrestrial foraging ants at site I do not maintain a fixed mosaic over time. In contrast, at site II ants maintain a fixed mosaic. The arboreally foraging ants reflect, to some extent, the pattern of the terrestrial foragers. A possible interpretation of these results is that dominant ants at site I contain competitive intransitivities that generate a changing mosaic, whereas dominant ants in site II are organized in a competitive hierarchy that generates a fixed mosaic.