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.

Data Collection
Data were collected using wet pitfall traps established across various patches within the Qassi glacier foreland and supplemented with data retrieved from the GEM (Global Ecological Monitoring) database for Kobbefjord. The specific timelines for data collection are as follows:

• Qassi 2015 Sampling:
  • Wet pitfall traps were set up on July 8, 2015, and continuous sampling occurred until August 7, 2015. Sampling was interrupted due to rainy weather and resumed from August 12 to August 20, 2015.
• Qassinnguit 2016 Sampling:
  • Wet pitfall traps were established on July 6, 2016, with continuous sampling until August 5, 2016. After a pause due to rain, sampling continued from August 10 to August 19, 2016.

Soil samples were collected at Qassi on August 7, 2015, and at Qassinnguit on August 5, 2016, to characterize environmental variables, specifically measuring soil water content and organic matter during dry weather conditions. NDVI (Normalized Difference Vegetation Index) measurements were taken on August 1, 2016, to assess vegetation biomass across the sampled patches.

Data Retrieval for Kobbefjord
Data for Kobbefjord were retrieved from the GEM database, which provided existing ecological data relevant to the study, allowing for a comparative analysis of predator-prey interactions across different environments. These data are shared under CC BY-SA 4 but are not included here. Access to GEM data may be requested via https://data.g-e-m.dk/.

Arthropod Identification and Analysis
Captured arthropods were identified to species or family level using standard taxonomic keys and references. COI barcoding was performed to enhance the reference library used for metabarcoding of predator gut contents. Most specimens were barcoded at the Canadian Centre for DNA Barcoding (CCDB), employing primers LCO1490 and HCO2198. Sanger sequencing of the amplicons was conducted, and the sequences were deposited in BOLD and GenBank. The density of arthropods was quantified based on the number of individuals captured in the pitfall traps. Soil samples underwent analysis to determine water and organic matter content.

Gut Content Analysis
The gut contents of arthropod predators collected during the study were analyzed using molecular techniques to determine the composition of their prey community. DNA metabarcoding was employed to identify various prey species present in the guts of predators, including linyphiid spiders, harvestmen, and ground beetles. This analysis provided critical insights into the trophic linkages between predators and their prey, supporting the understanding of predator-prey dynamics in the context of environmental changes.

Data Transformations
For statistical analysis, the following transformations were applied to the data:

• Intraguild predation (IGP) ratios were arcsine and square root transformed to meet the assumptions of normality for statistical tests.
• Distance to the glacier snout and time since deglaciation were log-transformed to stabilize variance and normalize the data distribution.
• Arthropod activity densities were also log-transformed for the same reasons.
• NDVI values were utilized without transformation, reflecting their original measurement values.

Qassi and Qassinnguit Dates and Sampling Information

• Soil Sampling Dates: August 7, 2015 (Qassi) and August 5, 2016 (Qassinnguit).
• NDVI Scanning Date: August 1, 2016.
• Wet Pitfall Trap Setup:
  • Qassi 2015: July 8 to August 7, resumed August 12 to August 20.
  • Qassinnguit 2016: July 6 to August 5, resumed August 10 to August 19.