Estación Biológica Cocha Cashu
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Assistants Dietary effects on the ecology and evolution of ants (F. Formicidae)
Principal Investigator:
Diane W. ("Dinah") Davidson
Professor of Biology
University of Utah 257 South, 1400 East
Salt Lake City, UT 84112-0840
Phone: 801-581-8392 Fax: 801-581-4668

In lowland tropical rain forests, ants can comprise up to 94% of individuals and 86% of biomass in canopy arthropod samples. Although commonly viewed as predators and scavengers, ants are regularly more abundant than their supposed prey. Extraordinary abundance usually characterizes just 1 or 2 ant species (per sample) which depend strongly on carbohydrate-rich plant and homopteran exudates for food. Though % nitrogen of exudates is low, lower delta 15N values in these ants than in predatory species indicate that the former obtain more of their (growth-limiting) nitrogen at a lower trophic level than do predators. Lower % dry weight N in exudate-feeders than in predators may indicate protein investment in protein-rich exoskeleton. Diets of abundant species have high CHO: protein ratios. CHOs in excess of those paired with protein for colony growth and reproduction may be directed at little cost to: (1) high tempo (high velocity) activity, correlated with high "dynamic densities" and rapid protein discovery; (2) defense of absolute territories (rare in ants generally, but more common in exudate-feeders than other ants), and (3) nitrogen-free offensive and defensive exocrine products. The nature of nitrogen-free defenses (volatile or non-volatile)appears to determine predation-risk for large-bodied, exudate-foraging ants in ways that have affected rates of exudate uptake. We are currently conducting experimental and comparative tests of the effects of dietary CHO:N ratio and predation risk on ant behavior.