| Summary: | Below- and above-ground arthropod communities were explored at a glacier foreland area in low Arctic Southwest Greenland aiming for a better understanding of the mechanisms behind the arthropod succession driven by increasing temperatures in the context of an Arctic climate change scenario. Arthropods were sampled in 2015 and 2016 along a downslope transect where the microclimate became warmer downhill a chronosequence towards a climax vegetation. The arthropod data sets were analyzed in relation to an environmental data set. Bottom-up controlled population developments were important in the early phase of the vegetation development while top-down prevailed in the later phase of the vegetation development. The shift from bottom-up to top-down cascades between arthropod predators and their potential prey populations was mainly driven by increasing temperatures away from the glacier. Structural equation modeling (SEM) shows bottom-up and top-down controlled food chains as bottom-up control was important for spider and harvestman populations while top-down control was important for ground beetle populations. These mechanisms are closely related to the hunting strategies of the predators as bottom-up mechanisms are connected to a sit-and-wait behavior while top-down mechanisms are related to active-search behavior. The SEM analyzes were supported by DNA metabarcoding as well as by the literature. A consequence of the strong top-down cascades in the later phase of the succession is high rates of intra-guild predation (IGP) among all arthropod predators. Particularly in the guts of the linyphiid spider, Collinsia holmgreni Thorell 1871, trophic linkages to other linyphiid and lycosid spiders were detected. The IGP ratio of C. holmgreni was negatively correlated with the activity density of available ground-living prey. Probably as a consequence of the high IGP among the linyphiid spiders, cold-adapted linyphiid species like C. holmgreni decreased in numbers downhill and became extinct in the warmer climax vegetation, ...
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