PARENT SESSION
Oral Session #55: Predator - Prey Interactions.
Presiding: R. Dueser
Wednesday, August 7. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.

Ants influence the distribution of forest-floor generalist predators and Collembola.

MOYA-LARAŅO, JORDI^*,1, WISE, DAVID¹, ¹ UNIVERSITY OF KENTUCKY, LEXINGTON, KENTUCKY

ABSTRACT- Although ants are major components of the biomass in most terrestrial ecosystems, few studies have investigated how ants influence the spatial distribution of other arthropods. In laboratory trials the centipede Lithobious, and the spider genera Gnaphosa, Titanoeca and Xysticus readily fed on the ants Aphaenogaster and Prenolepis. We conducted a field experiment in which twenty-four 1x1-m plots were provided with baits for ants (bread crumbs, tuna and maple syrup). Twenty-four unbaited plots were controls. Ant activity in baited plots was 28x higher than in control plots. At the end of the study, ant density was 2.5x higher in baited (127/m²) than control plots (51/m²) ). Densities of generalist predators that did not readily feed on ants in laboratory trials did not differ between experimental and control plots. Ant predators, however, showed a marginally significant increase (1.4x) in baited plots (p = 0.057), with Gnaphosa showing the strongest response followed by Lithobius. The myrmecophagic ant Neivamyrmex was more common in baited plots than in control plots. Collembola numbers were higher in baited plots (11/m²) ) relative to control plots (3/m²) ). Although the overall effect of ants on other arthropods was not strong, further analyses showed that ants may have a strong effect on the arthropod distribution, and that a combination of direct and indirect effects of different ant species, can explain most of the variance of other arthropod numbers. In the best-fitted 26 regression models explaining the densities of generalist predators and Collembola, ant densities explained more than 40% of the variance in both treatments. This contribution increased to 73% in the baited plots when ant activity was included. Different ant species, Collembola and predators significantly contributed to the different regression models with either positive or negative signs, suggesting that the responses to the increase in ant densities depended on the species involved in each plot, and that the existence of counteracting effects was the most likely explanation for the only moderate overall response to the baiting. These results suggest that ants are important in determining the distribution of generalist predators and Collembola in the forest floor.

KEY WORDS: ants, generalist predators, spiders, numerical responses