DOI: 10.5061/dryad.n5tb2rc81
title: Data from: Ecosystem age drives food web architecture of glacier retreat-formed fishless ponds in Greenland

description: Here, we studied the topology of food webs in newly created Arctic ponds
 formed by deglaciation, analyzing potential drivers such as environmental
 variables in 16 fishless ponds of contrasting ages (8 young, &lt;50
 years; 8 old, &gt;150 years) located on the rapidly retreating west
 coast of Greenland. Using gut content analysis of zooplankton and benthic
 macroinvertebrates, we constructed food webs and examined how food web
 metrics related to pond age and environmental variables. We also tested
 for differences in beta diversity and nestedness of prey and consumers
 between pond age classes. In young ponds, food items of zooplankton and
 macroinvertebrates represented a subset of those found in old ponds. Food
 webs in old ponds exhibited higher taxonomic richness, greater linkage
 density, and lower connectance, indicating greater stability. Pond age was
 the main explanatory factor for most food web metrics, followed by
 productivity proxies (total nitrogen and phytoplankton chlorophyll-a).
 While food webs in old ponds were not significantly associated with
 environmental variables, in young ponds, connectance and trophic niche
 overlap were significantly related to TN and Chl-a. These contrasting
 patterns suggest that food web topology becomes more complex and less
 dependent on environmental conditions as ponds age.
description: Samples were obtained during a single survey of ponds located on
 the western coast of Greenland. Pond age was estimated at the landscape
 level using current and historical ice-sheet maps and aerial photographs
 measuring distance to the ice front, rather than at the level of
 individual systems. Half of the ponds (n = 8) were located in an area
 where the glacier had retreated within the past 50 years (“young ponds”),
 while the other half were situated in an area deglaciated for at least 150
 years (“old ponds”). Stomach contents of
 macroinvertebrates and zooplankton were analyzed to reconstruct food webs.
 Using the relative abundance of food items by taxon and by system, we
 built diet matrices for each pond (<strong>file:
 data1.csv</strong>) to calculate trophic network metrics
 (connectance, linkage density, and trophic niche overlap). For graphical
 representation of networks, we also constructed edge lists for each pond,
 where each row represents a trophic interaction from a consumer to a
 resource (<strong>file: data2</strong>, folder with
 spreadsheets for network reconstruction). Based on
 consumer identifications by pond, we created a presence/absence matrix of
 consumers across sites (<strong>file: community
 cons.csv</strong>). Similarly, based on the food items found in
 guts, we created a presence/absence matrix of prey items across sites
 (<strong>file: community2.csv</strong>). From these matrices,
 we calculated overall beta diversity (βsor) and its components (turnover,
 βsim, and nestedness, βnes). Morphometric and
 environmental variables were measured in each pond: surface area and
 maximum depth (measured in situ), water pH, temperature, and electrical
 conductivity at the central point, as well as water samples for chemical
 analyses. Indicators of trophic state included total phosphorus (TP, μg
 L⁻¹), total nitrogen (TN, μg L⁻¹), and phytoplankton chlorophyll-a (Chl-a,
 μg L⁻¹) concentrations, as proxies of potential productivity. Differences
 between pond age groups were tested using two-tailed Mann–Whitney–Wilcoxon
 tests at α=0.05 (<strong>file: Environmental
 variables.csv</strong>). Relationships between
 food web metrics (number of food items, maximum trophic level,
 connectance, linkage density, and trophic niche overlap) and
 environmental, age, and morphometric variables were analyzed using
 Generalized Linear Models (GLM) (<strong>file:
 GLM_analysis.csv</strong>). All analyses were
 conducted in R using standard packages and functions, as described in the
 methodology section of the article. The accompanying script provides an
 example of each type of analysis; full details are available in the
 published paper.
description: # Data from: Ecosystem age drives food web architecture of glacier
 retreat-formed fishless ponds in Greenland Dataset DOI:
 [10.5061/dryad.n5tb2rc81](10.5061/dryad.n5tb2rc81) ## Description of the
 data and file structure Samples were obtained during a single survey of
 ponds located on the western coast of Greenland. Pond age was estimated at
 the landscape level using current and historical ice-sheet maps and aerial
 photographs measuring distance to the ice front, rather than at the level
 of individual systems. Half of the ponds (n = 8) were located in an area
 where the glacier had retreated within the past 50 years (“young ponds”),
 while the other half were situated in an area deglaciated for at least 150
 years (“old ponds”). Macroinvertebrates and zooplankton were sampled to
 reconstruct the food webs of each pond based on gut content analyses.
 These data were linked via GLMs to the ecosystem age and to morphometric
 and environmental variables.  The datasheets correspond to: 1. A diet
 matrix from one pond (as an example) for calculating food web metrics. 2.
 A compressed folder containing the files necessary for the representation
 of the food webs. This compressed folder must be decompressed before
 running the script, as the R scripts assume the folder is located in the
 same directory from which they are executed. 3. A presence/absence species
 matrix for both prey and consumers (for beta diversity calculations). 4. A
 sheet containing environmental data. 5. A sheet integrating environmental
 data and food web metrics (for GLM analysis). ### Files and variables ####
 File: Environmental_variables.csv **Description:** Environmental, age and
 morphometric characteristics of the 16 Greenlandic ponds studied #####
 Variables * System: Id Pond * Age: Pond age (young or old) * Area: Pond
 Area, m^2^ * Depth: maximum water depth (m) * Chl-a: chlorophyll-a water
 concentration (µg L-1) * TN: total nitrogen concentration in water (µg
 L-1) * TP: total phosphorus concentration in water (µg L-1) * T: water
 temperature (°C) * K: electrical conductivity (µS cm^-1^) * pH: water pH
 #### File: GLM_analysis.csv **Description:** Environmental, age and
 morphometric characteristics of the 16 Greenlandic ponds
 studied. Additionally, the dataset includes community-level variables such
 as food web metrics ##### Variables * System: Pond id * Age: Pond age
 class * Area (m2): pond surface area (m^2^) * TP (µg/L): total phosphorus
 concentration in water (µg L-1) * TN (µg/L): total nitrogen concentration
 in water (µg L-1) * Chl-a (µg/L): chlorophyll-a water concentration (µg
 L-1) * pH: water pH * Depth (m): maximum water depth (m) * Cond
 (µS/cm): electrical conductivity (µS cm^-1^) * Temp (C): water temperature
 (°C) * Number of links: Result of the species accumulation curve, where
 the number of items consumed by the consumers in each system was
 standardized by the number of stomach analyzed. That is, the expected
 number of total items consumed per pond. * Max. trophic level: Maximum
 trophic position for each pond * Connectance: Number of effective
 connections divided by the total number of possible links (taxa). C=
 2L/S(S-1), where L is the number of effective connections and S is the
 number of taxa in the web. * Linkage density: Calculated as the number of
 links for each taxa. LD= L/S, where L is the number of links in the web
 and S is the number of taxa. * Trophic niche overlap: Use of the same food
 item by two or more taxa or individuals. At global level, it is calculated
 as the average of all occurring overlaps. #### File: community2.csv
 **Description:** presence/absence matrix of food items in all sampling
 sites was constructed (for beta diversity calculations). #### File:
 Data1.csv **Description:** Diet matrix from one pond (as an example) for
 calculating food web metrics. The first row and the column headers
 correspond to the species in the network (both consumers and food items).
 The values within the matrix indicate the relative abundance of each
 dietary item. #### File: community_cons.csv
 **Description:** presence/absence matrix of cpnsumers in all sampling
 sites was constructed (for beta diversity calculations). #### File:
 Data2.zip **Description:** Compressed folder containing the files
 necessary for the representation of the food webs. This compressed folder
 must be decompressed before running the script, as the R scripts assume
 the folder is located in the same directory from which they are executed.
 Files in the compressed folder:  1- nodes: Taxonomic identity of every
 species in the food web. Nodes: species present in the food web; Category:
 trophic position of each species in the food web. 2- trophic.links: list
 of interactions (-edge list-, where each row represents a trophic
 interaction from a consumer to a resource). Resource: Food items;
 Consumer: consumers 3- properties: Input file needed by the Cheddar
 package to import the community dataset and visualize the networks. ####
 File: López-Rodríguez_et_al._2024_FINAL_R_script.R **Description:** R
 script with the code used to perform the analyses. ## Code/software The
 data analysis was performed using common R packages and functions, as
 detailed in the methodology of the paper. The analysis included GLM
 and model selection procedures, all of which are standard approaches in
 ecological research. These models are implemented with widely used
 packages for statistical modeling. Food web metrics were calculated using
 the bipartite and Cheddar packages. Beta diversity analyses were also
 performed using the betapart package.