Arrival and survival: Influences of a dominant, ground-nesting ant on arboreal ant colonies and communities

Background/Question/Methods

Ecologists have long been fascinated with community assembly processes. Ants are ubiquitous in the tropics and found across all types of vegetation, thus making them ideal organisms for studies of community structure. Several factors are cited as driving community assembly of ants including competition, dispersal, and environmental conditions. Dominant species within a community are frequently defined as strong competitors thought to dictate competitive outcomes and community assembly. Working in uniformly managed coffee-agroecosystems, we used both surveys and experiments to examine the effects of a dominant ground-nesting ant (Pheidole synanthropica) on the recruitment and establishment of a arboreal, twig-nesting ant community. We established six, 20×20m plots and surveyed all ants on the ground and on coffee plants. Three sites had high densities of P. synanthropica, three others had low densities of P. synanthropica. To test the effect of P. synanthropica on twig-nesting ant colony recruitment, we added nesting resources to coffee plants (i.e. bamboo twigs) every four months for a year. At each interval, we collected and identified all ants found in the twigs. We then compared the community composition of ants on the ground, on coffee plants, and in bamboo twigs in plots with high and low P. synanthropica density.

Results/Conclusions

We found that high-density P. synanthropica sites had 40, 76, and 59% fewer species in the ground, coffee and twigs as compared to low-density P. synanthropica sites. Species composition also significantly differed between high- and low-density P. synanthropica sits for all three ant assemblages. Total recruitment of twig-nesting ant colonies to plots with high P. synanthropica density was significantly lower than recruitment in plots with low P. synanthropica density, but only for one sampling period. We also found, however, both strong positive and negative species-specific effects of P. synanthropica on twig-nesting species, which likely contribute to the different species compositions found between the plots with high and low P. synanthropica density. These results provide evidence that foraging patterns of dominant ground nesting ants have strong and significant effects on ground-foraging, coffee-foraging and even twig-nesting ant assemblages. The effect on twig-nesting ants is surprising given that competition between P. synanthropica and twig-nesting ant assemblage should be limited to competition of food resources rather than food and nesting resources. We further suggest, based on experimental results of twig-nesting ant recruitment, that this dominant species affects both colonization and establishment of many species that scale up to community-wide compositional differences.