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Title: Trophic cascades in a cranberry marsh: Can detritus-removal improve biological control

Author
item VAN ZOEREN, JANET - University Of Wisconsin
item Steffan, Shawn

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 1/18/2015
Publication Date: 3/12/2015
Citation: Van Zoeren, J., Steffan, S.A. 2015. Trophic cascades in a cranberry marsh: Can detritus-removal improve biological control [abstract]. Wisconsin Ecology Annual Spring Symposium. Paper No. 8.

Interpretive Summary:

Technical Abstract: Biological pest control is predicated on the concept that plants are protected when carnivores suppress herbivore populations. However, many factors, including detritus-based food-chains, may re-shape the effectiveness of predators in a given agro ecosystem. The addition of detrital subsidies, such as mulch, has been shown to change the community dynamics between generalist predators, herbivores, and detritivores, with varying effects on crop protection. We re-examined this question by removing detritus instead of subsidizing it; a spring flood in commercial cranberry production serves to remove detritus as well as enacting pest suppression. We hypothesized that with the removal of detritus, detritivores, a major prey source for generalist predators, will decline. This should force the predator community following the flood to feed increasingly on herbivores, thereby generating more effective biological pest control. To test this hypothesis, cranberry beds were assigned to a spring flood or a spring pesticide treatment, and arthropod diversity and density were assessed for the following six. Detritivore populations rapidly declined following both flood and spray treatments, and did not recover. Spider populations in the flooded beds rose markedly by week-2 and stayed consistently, significantly higher than in the sprayed beds. Spiders commonly prey upon mites and springtails, and it is possible that differences in detritivore numbers between the flood and spray treatments were dampened by high spider numbers. Further, low detritivore densities throughout the summer suggest that spiders may have continued feeding on them. Parasitoids targeting moth pests were much higher in the flooded beds, suggesting that sprays have a detrimental impact on the ability of specialist carnivores to reduce herbivore numbers. Flooding, therefore, may support spider and parasitoid populations that, together, reduce both detritivore and herbivore populations.