DENSITY PATTERNS OF PIPER ANT-PLANTS AND ASSOCIATED ARTHROPODS - TOP-PREDATOR TROPHIC CASCADES IN A TERRESTRIAL SYSTEM

Top-predator (fourth-trophic-level) controlled trophic cascades are th ought to be uncommon in terrestrial systems, but actual quantitative t ests and comparisons of bottom-up and top-down Forces in systems with more than three linear trophic levels are rare. Here, we describe the density patterns of the archropod community associated with Piper ant- planes in Costa Rican wet forests. Consumers in this community compris e a complex, interacting web of herbivores, predaceous ants, and preda tors of ants. Although the hollow stems and petioles of the Piper plan ts provide some protection to resident ants from predation, specialize d Dipoena spiders and Phyllobaenus beetles exploit Pheidole ants inhab iting Piper plants. We report abundance patterns of plants, ants and p redators in four forests. These patterns of abundance are consistent w ith predictions of top-down cascades across four trophic levels when t he top predators are effective (beetles). We discuss how top-down and bottom-up forces may interact in systems with less effective top preda tors (spiders).