Subsidy from the detrital food web, but not microhabitat complexity, affects the role of generalist predators in an aboveground herbivore food web
Subsidy from the detrital food web, but not microhabitat complexity, affects the role of generalist predators in an aboveground herbivore food web
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DOI：
10.1111/j.0030-1299.2008.16361.x
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发表时间：
2008-04-01
期刊：
影响因子：
3.4
通讯作者：
Scheu, Stefan
中科院分区：
文献类型：
--
作者：
Birkhofer, Klaus;Wise, David H.;Scheu, Stefan
多功能捕食者的活动和密度，如步甲，漫游甲虫和蜘蛛，可能会增加响应：（1）增加的猎物从地下子系统的可用性和/或（2）增加的地上植被的复杂性。有机农业的做法支持分解人口和提高栖息地的复杂性，由于增加杂草密度。多面手捕食者对这种地下或地上变化的反应可能会影响地上食物网中食草动物的捕食率。我们测试了这一假设在一个重复的田间试验中进行的冬小麦田，在那里增加捕食者的活动可能会导致改善控制草食性害虫。在一个交叉设计中，我们增加和降低分解猎物的密度，并操纵植被的复杂性，使用人工植物，以研究结构复杂性的影响，从植物吸引的额外的猎物的影响隔离。弹尾目等节虫在土壤杀虫剂处理的地块中表现出最低的活动密度（AD），在未处理的地块和接受碎屑补贴的地块中AD逐渐增加。步甲和爬行蜘蛛没有响应isotomid猎物的可用性增加，他们意外地显示出较高的AD在结构不太复杂的情节。蚜虫密度反映了正向反应的isotomids碎屑补贴，这表明蚜虫受益于减少捕食，由于捕食者切换到丰富的猎物在分解子系统。表面活跃的捕食者的数值响应的情况下，显然加强了这种间接影响的isotomids蚜虫。我们的研究结果表明，间接的捕食介导的猎物-猎物的相互作用可以减少有害生物抑制的有益影响的碎屑补贴。我们进一步证明，通才捕食者本身可能不会受益于结构的复杂性。这两个结果都记录了与支持通才捕食者的管理实践相关的挑战，因为这些措施不一定能改善对食草动物的抑制。
The activity and density of generalist predators, such as carabid beetles, rove beetles 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 beetles 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 apparently 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.