title: A multifaceted trophic cascade in a detritus-based system: density-, trait-, or processing-chain-mediated effects?
abstract: We investigated three pathways by which predators on an intermediate trophic level may produce a trophic cascade in detritus-based systems. Predators may increase lower trophic levels (bacteria) by reducing density of bacteriovores, by altering behavior of bacteriovores, and by processing living bacteriovores into carcasses, feces, and dissolved nutrients that are substrates for bacteria. We tested these pathways in laboratory experiments with mosquitoes in water-filled containers. LarvalToxorhynchites rutilusprey on larvalAedes triseriatus, which feed on bacteria. Using containers stocked with oak leaf infusion as a bacterial substrate, we compared bacterial productivity at 7 and 14 days for: prey alone; prey with a predator; and prey with predation cues but no predator. Controls contained no larvae, either with predation cues or without cues. Predation cues in the control treatment increased bacterial abundance at 7 days, but this effect waned by 14 days.Aedes triseriatuslarvae reduced bacterial abundance significantly at 14 days. Predator cues and real predation both eliminated the negative effect ofA. triseriatuson bacterial abundance. Predation cues reduced survivorship ofA. triseriatuslarvae at 14 days, however this effect was smaller than the effect of real predation. We further tested effects of residues from predation as cues or as detritus in a second experiment in whichA. triseriatuswere killed at similar rates by: real predators;mechanical damage without the predator and carcasses left as detritus; or mechanical damage and carcasses removed. No prey larvae were killed in controls. Bacterial productivity was greater with real predation than in all other treatments and greater when prey larvae were killed or killed and removed, than in controls. Thus we find evidence that all three pathways contribute to the trophic cascade fromT. rutilusto bacteria in tree hole systems.
authors.affiliation: Programa de Pós Graduação em Entomologia, Departmento de Entomologia, Universidade Federal de Viçosa, Viçosa MG 36570-000, Brazil.
authors.forename: Daniel
authors.initials: D
authors.lastname: Albeny-Simões
authors.affiliation: School of Biological Sciences, Illinois State University, Normal IL, 61790-4120 USA.
authors.forename: Ebony G
authors.initials: EG
authors.lastname: Murrell
authors.affiliation: Programa de Pós Graduação em Entomologia, Departmento de Entomologia, Universidade Federal de Viçosa, Viçosa MG 36570-000, Brazil.
authors.forename: Evaldo F
authors.initials: EF
authors.lastname: Vilela
authors.affiliation: School of Biological Sciences, Illinois State University, Normal IL, 61790-4120 USA.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Juliano
keywords: Aedes triseriatus; Toxorhynchites; density-mediated indirect interaction; predation; processing chain interaction; trait-mediated indirect interaction; trophic cascade
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