Interactions among predators and the cascading effects of vertebrate insectivores on arthropod communities and plants.
Theory on trophic interactions predicts that predators increase plant biomass by feeding on herbivores, an indirect interaction called a trophic cascade. Theory also predicts that predators feeding on predators, or intraguild predation, will weaken trophic cascades. Although past syntheses have confirmed cascading effects of terrestrial arthropod predators, we lack a comprehensive analysis for vertebrate insectivores-which by virtue of their body size and feeding habits are often top predators in these systems-and of how intraguild predation mediates trophic cascade strength. We report here on a meta-analysis of 113 experiments documenting the effects of insectivorous birds, bats, or lizards on predaceous arthropods, herbivorous arthropods, and plants. Although vertebrate insectivores fed as intraguild predators, strongly reducing predaceous arthropods (38%), they nevertheless suppressed herbivores (39%), indirectly reduced plant damage (40%), and increased plant biomass (14%). Furthermore, effects of vertebrate insectivores on predatory and herbivorous arthropods were positively correlated. Effects were strongest on arthropods and plants in communities with abundant predaceous arthropods and strong intraguild predation, but weak in communities depauperate in arthropod predators and intraguild predation. The naturally occurring ratio of arthropod predators relative to herbivores varied tremendously among the studied communities, and the skew to predators increased with site primary productivity and in trees relative to shrubs. Although intraguild predation among arthropod predators has been shown to weaken herbivore suppression, we find this paradigm does not extend to vertebrate insectivores in these communities. Instead, vertebrate intraguild preda-tion is associated with strengthened trophic cascades, and insectivores function as dominant predators in terrestrial plant-arthropod communities.
Mooney
Kailen A
KA
Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697-2525, USA. mooneyk@uci.edu
Gruner
Daniel S
DS
Barber
Nicholas A
NA
Van Bael
Sunshine A
SA
Philpott
Stacy M
SM
Greenberg
Russell
R
D000818:Animals; D001181:Arthropods / Q000502:physiology*; D018533:Biomass; D049628:Body Size; D005247:Feeding Behavior; D007313:Insecta; D010944:Plants; D011157:Population Dynamics; D011235:Predatory Behavior; D018401:Sample Size; D015398:Signal Transduction; D014197:Trees