Advanced

Subsidy from the Detrital Food Web, but Not Microhabitat Complexity, Affects the Role of Generalist Predators in an Aboveground Herbivore Food Web

Birkhofer, Klaus LU ; Wise, David H. and Scheu, Stefan (2008) In Oikos 117(4). p.494-500
Abstract
The activity and density of generalist predators, such as carabid beedes, rove beedes and spiders, may increase in response to: (1) increased availability of prey from the belowground subsystem and/ or (2) enhanced complexity of aboveground vegetation. Organic farming practices support decomposer populations and enhance habitat complexity due to an increased weed density. A response by generalist predators to such below-or aboveground changes could affect predation rates on herbivores in the aboveground food web. We tested this hypothesis in a replicated field experiment conducted in a winter wheat field, where increased predator activity could lead to improved control of herbivorous pests. In a crossed design, we increased and lowered... (More)
The activity and density of generalist predators, such as carabid beedes, rove beedes and spiders, may increase in response to: (1) increased availability of prey from the belowground subsystem and/ or (2) enhanced complexity of aboveground vegetation. Organic farming practices support decomposer populations and enhance habitat complexity due to an increased weed density. A response by generalist predators to such below-or aboveground changes could affect predation rates on herbivores in the aboveground food web. We tested this hypothesis in a replicated field experiment conducted in a winter wheat field, where increased predator activity could lead to improved control of herbivorous pests. In a crossed design, we increased and lowered densities of decomposer prey, and manipulated vegetation complexity using artificial plants in order to examine the effect of structural complexity in isolation from effects of plant-attracted additional prey. Isotomid Collembola exhibited lowest activity-densities (AD) in plots treated with soil insecticide and had gradually increasing AD in untreated plots and plots receiving detrital subsidies. Carabid beedes and cursorial spiders did not respond to increased availability of isotomid prey, and they unexpectedly displayed higher AD in the structurally less-complex plots. Aphid density mirrored the positive response of isotomids to detrital subsidies, suggesting that aphids benefited from reduced predation due to predators switching to abundant prey in the decomposer subsystem. The absence of a numerical response by surface-active predators apparendy strengthened this indirect effect of isotomids on aphids. Our results suggest that indirect predator-mediated prey-prey interactions can reduce beneficial effects of detrital subsidies on pest suppression. We further demonstrated that generalist predators may not per se benefit from structural complexity. Both results document the challenges associated with management practices that support generalist predators, as these measures may not necessarily improve herbivore suppression. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Oikos
volume
117
issue
4
pages
494 - 500
publisher
Wiley-Blackwell
external identifiers
  • scopus:41149150443
ISSN
1600-0706
DOI
10.1111/j.0030-1299.2008.16361.x
language
English
LU publication?
yes
id
019c517f-2b03-4a5a-b4d6-d68121cfda15 (old id 2440500)
alternative location
http://www.scopus.com/inward/record.url?eid=2-s2.0-41149150443&partnerID=40&md5=306eb3bb429bdf83c51ac908703b5945
date added to LUP
2012-06-18 16:15:51
date last changed
2017-09-03 03:53:33
@article{019c517f-2b03-4a5a-b4d6-d68121cfda15,
  abstract     = {The activity and density of generalist predators, such as carabid beedes, rove beedes and spiders, may increase in response to: (1) increased availability of prey from the belowground subsystem and/ or (2) enhanced complexity of aboveground vegetation. Organic farming practices support decomposer populations and enhance habitat complexity due to an increased weed density. A response by generalist predators to such below-or aboveground changes could affect predation rates on herbivores in the aboveground food web. We tested this hypothesis in a replicated field experiment conducted in a winter wheat field, where increased predator activity could lead to improved control of herbivorous pests. In a crossed design, we increased and lowered densities of decomposer prey, and manipulated vegetation complexity using artificial plants in order to examine the effect of structural complexity in isolation from effects of plant-attracted additional prey. Isotomid Collembola exhibited lowest activity-densities (AD) in plots treated with soil insecticide and had gradually increasing AD in untreated plots and plots receiving detrital subsidies. Carabid beedes and cursorial spiders did not respond to increased availability of isotomid prey, and they unexpectedly displayed higher AD in the structurally less-complex plots. Aphid density mirrored the positive response of isotomids to detrital subsidies, suggesting that aphids benefited from reduced predation due to predators switching to abundant prey in the decomposer subsystem. The absence of a numerical response by surface-active predators apparendy strengthened this indirect effect of isotomids on aphids. Our results suggest that indirect predator-mediated prey-prey interactions can reduce beneficial effects of detrital subsidies on pest suppression. We further demonstrated that generalist predators may not per se benefit from structural complexity. Both results document the challenges associated with management practices that support generalist predators, as these measures may not necessarily improve herbivore suppression.},
  author       = {Birkhofer, Klaus and Wise, David H. and Scheu, Stefan},
  issn         = {1600-0706},
  language     = {eng},
  number       = {4},
  pages        = {494--500},
  publisher    = {Wiley-Blackwell},
  series       = {Oikos},
  title        = {Subsidy from the Detrital Food Web, but Not Microhabitat Complexity, Affects the Role of Generalist Predators in an Aboveground Herbivore Food Web},
  url          = {http://dx.doi.org/10.1111/j.0030-1299.2008.16361.x},
  volume       = {117},
  year         = {2008},
}