DOI: 10.5061/dryad.qfttdz0qt
title: Arthropod food webs in the foreland of a retreating Greenland glacier: Integrating molecular gut content analysis with Structural Equation Modelling

description: 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.
description: <strong>Data Collection</strong><br>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:
 <strong>Qassi 2015 Sampling</strong>:
 Wet pitfall traps were set up on <strong>July
 8, 2015</strong>, and continuous sampling occurred until
 <strong>August 7, 2015</strong>. Sampling was interrupted due
 to rainy weather and resumed from <strong>August 12 to August 20,
 2015</strong>. 
 <strong>Qassinnguit 2016 Sampling</strong>: 
 Wet pitfall traps were established on <strong>July 6,
 2016</strong>, with continuous sampling until <strong>August
 5, 2016</strong>. After a pause due to rain, sampling continued from
 <strong>August 10 to August 19, 2016</strong>.
 Soil samples were collected
 at Qassi on <strong>August 7, 2015</strong>, and at
 Qassinnguit on <strong>August 5, 2016</strong>, 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
 <strong>August 1, 2016</strong>, to assess vegetation biomass
 across the sampled patches. <strong>Data
 Retrieval for Kobbefjord</strong><br>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/.
 <strong>Arthropod Identification and
 Analysis</strong><br>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. <strong>Gut Content
 Analysis</strong><br>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.
 <strong>Data Transformations</strong><br>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 <strong>Soil Sampling
 Dates</strong>: August 7, 2015 (Qassi) and August 5, 2016
 (Qassinnguit). <strong>NDVI Scanning
 Date</strong>: August 1, 2016. 
 <strong>Wet Pitfall Trap Setup</strong>: 
 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.
description: # Arthropod food webs in the foreland of a retreating Greenland glacier:
 Integrating molecular gut content analysis with Structural Equation
 Modelling ## Authors: **Corresponding author**: Paul Henning Krogh, Aarhus
 University, [phk@ecos.au.dk](mailto:phk@ecos.au.dk), ORCID:
 [https://orcid.org/0000-0003-2033-553X](https://orcid.org/0000-0003-2033-553X) Ejgil Vestergård Gravesen, [Molecular Ecology], [ejgilg@gmail.com](mailto:ejgilg@gmail.com) Lenka Dušátková, Masaryk University Kacie Athey, University of Illinois at Urbana-Champaign Jiayi Qin, Novo Nordisk (Denmark) **Summary:** This dataset includes information on arthropod sampling and environmental variables collected at the Qassi glacier foreland and Kobbefjord during the summers of 2015 and 2016. The data were used for Structural Equation Modeling (SEM) to analyze food web interactions and the impact of environmental factors. Combining DNA gut content analysis with SEM based on arthropod activity density provides insights into bottom-up and top-down control mechanisms within arthropod populations, their relationship with environmental variables, and shifts in these mechanisms across different stages of vegetation development. **Description of Data File Structure and Contents:** The dataset is organized into one Excel sheet with four folders: 1. **‘Env. and arthropods’**: Contains environmental variables and measures of arthropod activity density. 2. **‘IGP SEM2’**: Contains data for Intraguild Predation (IGP) used for SEM analysis. 3. **‘Metabarcoding Results’**: Lists the arthropod gut content of each individual specimen analyzed in the study. **Version Notes:** The initial version of this data included one sheet named 'Data for SEM', which contains similar information to the newer version but with slightly different header names. The second version includes data specifically used for SEM2. Variables included in the SEM1 model are marked with an 'X'. For IGP SEM2, the ground-living prey for *C. holmgreni* was based on activity densities of collembolans, aphids, and the mites Eupodoidae, Bdelloidae, and Bryobia, except for Erythraeoidea, which were not detected in the gut. **Notes on Missing Data:** * Empty cells indicate "N.D." (Not Determined). * The variable "Environmental variables 1_Time since deglaciation, years_X" was not determined in 2015 except for patches A to G. * The variable "Environmental variables 5_NDVI_X" was only assessed in 2016. **Environmental Variables Included:** * Meters Above Sea Level (MASL) * Distance to Glacier Snout (m) * NDVI (Normalized Difference Vegetation Index) * Mean Lichen Diameter (mm) * Time Since Deglaciation (years: 0 to 2500) * Soil Water Percentage in the Topsoil * Organic Matter Percentage in the Topsoil **Arthropod Activity Densities:** * Arthropod Predators * Parasitoids * Mites * Collembola * Diptera