| Summary: | Arthropod food webs were explored in a glacier foreland area in West Greenland using a combination of structural equation modelling (SEM) and DNA gut content analysis. Arthropod predators and their (arthropod) prey animals were sampled with traditional “wet” pitfall traps and their numbers were analyzed using structural equation modelling (SEM) in relation to a set of environmental variables. The result of the SEM analysis was compared with DNA gut content analysis, where arthropod predators were caughed alive in “dry” pifall traps before the gut content analysis as we would like to know how bottum-up or top-down mechanisms influence predator and prey animal numbers. We also want to know how the degree of vegetation cover influence prey capture by different predators as we expect different hunting strategies may have an influence on the capture rates of the different prey animals. The structural equation modelling (SEM) suggests that the spider populations in the foreland area may be involved in bottom-up regulated food chains in relation to the numbers of available flies as well as to the abundance of the collembolan Isotoma anglicana. DNA gut content analysis support that the spiders may be subject to bottom-up regulation by collembolans, as we found the same pattern of prey species composition in the environmental surroundings as in the gut content of the spiders. DNA gut content analysis shows that the spider Collensia holmgreni living in vegetated patches feed on a broad spectrum of available prey animals (18 arthropod species and families), including collembolans, dipterans, harvestmen, mites and maybe larvae of the ground beetle Nebria rufescens. C. holmgreni also feed (extensively) on other available linyphiid spiders like Oreoneta frigida and Improphantes complicates as well as the lycosid Arctosa insignita. The SEM analysis revealed a very significant (positive) relationship between the number of spiders and the number of the parasitic wasp (Aclastus borealis) that prey on spider eggs. A. borealis is supposed to attack the cocoons of linyphiid spiders. The SEM analysis may also suggest that the harvestman, Mitopus morio, is involved in bottom-up food chains feeding on flies and ground beetle (Nebria rufescens) larvaes. The DNA gut content analysis confirms this suggestion as Chironomidae, Muscidae and Simuliidae flies, linyphiid spiders, Isotomidae collembolans as well as N. rufescens ground beetle (larvae) are important prey animals for M. morio. M. morio also has a broad food spectrum involving 24 different species and families.
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