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. Larval Toxorhynchites rutilus prey on larval Aedes 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 triseriatus larvae reduced bacterial abundance significantly at 14 days. Predator cues and real predation both eliminated the negative effect of A. triseriatus on bacterial abundance. Predation cues reduced survivorship of A. triseriatus larvae 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 which A. triseriatus were 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 from T. rutilus to bacteria in tree hole systems.
Highlights
Trophic cascades occur when direct or indirect effects of predators on prey cause an indirect increase in abundance of the basal trophic level that is the food of the prey (Pace et al 1999, Shurin et al 2002)
Bacterial productivity was significantly affected by time (F1,35 1⁄4 5.65, P 1⁄4 0.0230), by treatment (F4,35 1⁄4 19.02, P 1⁄4 0.0001), and by treatment-time interaction (F4,35 1⁄4 8.15, P 1⁄4 0.0001)
We found evidence that all three kinds of effects are present in the trophic cascade from T. rutilus through A. triseriatus to bacteria
Summary
Trophic cascades occur when direct or indirect effects of predators on prey cause an indirect increase in abundance of the basal trophic level that is the food of the prey (Pace et al 1999, Shurin et al 2002). Predator consumption of prey may produce additional detritus in the form of predator feces, excreted nitrogenous waste, and partially eaten prey, releasing nutrients that fuel the growth of the basal trophic level, a phenomenon characterized as ‘‘nutrient cycling’’ in systems dominated by periphyton and phytoplankton (Costa and Vonesh 2013). This effect of predator feeding is likely in detritus-based systems, where bacteria are the basal trophic level, and it is better described as a ‘‘processing chain interaction’’ (PCI) (Heard 1995). In detritus-based systems, predators may process living tissue of bacteriovores into detritus, making substrates available to decomposers such as bacteria
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
