LINKING A PREDATOR'S FORAGING BEHAVIOR WITH ITS EFFECTS ON HERBIVORE POPULATION SUPPRESSION

Abstract

The view of terrestrial arthropod communities as potentially exhibiting a mixture of three- and four-trophic-level dynamics creates a new challenge for researchers: the indeterminacy of predator function. Here we evaluate two predictions linking a predator's foraging behavior with its likely ecological role: (1) widely foraging predators may act as effective regulators of sedentary herbivore populations, and (2) sit-and-wait predators are unlikely to regulate sedentary herbivore populations but may act as top predators, consuming widely foraging intermediate predators and allowing herbivore populations to escape from control. We tested these predictions by manipulating the predator community associated with a sedentary herbivore, the spider mite Tetranychus cinnabarinus, feeding on papaya, Carica papayae. The predators included a widely foraging specialist consumer of spider mites, the ladybird beetle Stethorus siphonulus, and a sit-and-wait generalist predator, the tangle-web spider Nesticodes rufipes. The experiments provided support for both predictions. The widely foraging predator Stethorus when tested alone was capable of effective suppression of spider mite populations. In contrast, the sit-and-wait predator, Nesticodes, never suppressed spider mites. Instead, Nesticodes consistently increased the population growth rates of spider mites. This effect was most likely due to Nesticodes suppressing populations of the intermediate predator Stethorus. Our results underscore the presence of both three- and four-trophic-level dynamics within this arthropod community and begin to address the challenging problem of the indeterminacy of predator function.