Organizational Complexity in Ecological Foodwebs: Experimental Analysis of Interaction Strength in an Old-Field System

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9508604 Schmitz This study will evaluate the importance of direct and indirect species interactions in structuring a terrestrial old-field food web. Insight into species interactions will be obtained through detailed work in natural field settings involving plants, insect herbivores (grasshoppers, katydids, and beetles) and carnivores (hunting spiders). The study will test a key hypothesis in food-web ecology that the strength of effects of one species on another will depend on species composition of the food web and the direct and indirect ways the two species interact through their linkages will other species in the system. Field experiments will be conducted to quantify precisely and reliably the kinds of species interactions, their strengths and the network of pathways through which the effects of species interactions pass. Experimental food webs with varying numbers of species of old-field herbs and grasses, insect herbivores and spiders will be assembled in enclosure cages in the field to quantify the effect of increasing species diversity on species interactions in a food web. The experiments will also evaluate whether or not food-web dynamics become altered if food-web structure is reduced through species removals. This research will provide important information on the way species in natural old-field systems become linked together and it will offer insight into what happens when these linkages are disrupted by natural or human disturbances. This information is crucial for the conservation of biological diversity. Many ecologists have suggested that a reduction in biodiversity that disrupts the network of species linkages can have serious impacts on the dynamics of natural food webs.