Arthropod food webs in the foreland of a retreating Greenland glacier: Integrating molecular gut content analysis with Structural Equation Modelling

The Arctic has warmed nearly four times faster than the global average
since 1979, resulting in rapid glacier retreat and exposing new glacier
forelands. These forelands offer unique experimental settings to explore
how global warming impacts ecosystems, particularly for highly
climate-sensitive arthropods. Understanding these impacts can help
anticipate future biodiversity and ecosystem changes under ongoing warming
scenarios. In this study, we integrate data on arthropod diversity from
DNA gut content analysis—offering insight into predator diets—with
quantitative measures of arthropod activity density at a Greenland glacier
foreland using Structural Equation Modelling (SEM). Our SEM analysis
reveals both bottom-up and top-down controlled food chains. Bottom-up
control, linked to sit-and-wait predator behavior, was prominent for
spider and harvestman populations, while top-down control, associated with
active search behavior, was key for ground beetle populations. Bottom-up
controlled dynamics predominated during the early stages of vegetation
succession, while top-down mechanisms dominated in later successional
stages further from the glacier, driven largely by increasing
temperatures. In advanced successional stages, top-down cascades
intensify intraguild predation (IGP) among arthropod predators. This is
especially evident in the linyphiid spider Collinsia holmgreni, whose diet
included other linyphiid and lycosid spiders, reflecting high IGP. The IGP
ratio in C. holmgreni negatively correlated with the activity-density of
ground-dwelling prey, likely contributing to the local decline and
possible extinction of this cold-adapted species in warmer,
late-succession habitats where lycosid spiders dominate. These findings
suggest that sustained warming and associated shifts in food web dynamics
could lead to the loss of cold-adapted species, while brief warm events
may temporarily impact populations without lasting extinction effects.