Top-down and bottom-up control of benthic grazers as key species in stream biomanipulation

本计画的重点是附着生物与溪栖食草昆虫之间的相互作用。核心问题是昆虫食草动物，如蜉蝣幼虫是否是关键物种在流食物网，因此，能够用于生物操纵的方法。计划在不同环境条件下进行食草动物和附生生物之间相互作用的实验。为了调查对食草动物的自上而下的影响，将进行不同捕食者制度的成对实地实验。此外，在室外围隔中，最佳的食草动物密度，以控制在春季高峰期的附生生物将进行调查。最后，在实验室围隔实验中，将量化农药对食草动物的影响。具有直接影响的杀虫剂可以归类为自上而下的影响，而除草剂对生物膜群落中的附着生物的数量和质量有影响，因此，通过自下而上的影响间接作用于食草动物。这些相互关联的实验结果将揭示哪些因素对控制食草动物很重要，哪些因素对它们的活动有不利影响。

The focal point of this project is the interaction between periphyton and stream insect grazers. The central question is whether insect grazers like mayfly larvae are keystone species in stream food webs and, thus, are able to be used in a biomanipulation approach. Experiments as to the interactions between grazers and periphyton under different environmental conditions are planned. To investigate the top-down impact on grazers, a pairwise field experiment with different predator regimes will be carried out. Furthermore, in outdoor mesocosms the optimal grazer density to control periphyton during the spring peak will be investigated. Finally, in laboratory mesocosm experiments the effects of pesticides on grazers will be quantified. Insecticides with direct effects can be categorised as top-down impact while herbicides have an influence on quantity and quality of periphyton in the biofilm community and, therefore, act indirectly via bottom-up effects on the grazers. The results of these interconnected experiments will reveal which factors are important to control grazers and which have adverse effects on their activity.