DOI: 10.5061/dryad.kf2553j
title: Data from: Progressive sensitivity of trophic levels to warming underlies an elevational gradient in ant-aphid mutualism strength

description: Although species interactions are often proposed to be stronger at lower
 latitudes and elevations, few studies have evaluated the mechanisms
 driving such patterns. In this study, we assessed whether, and by which
 mechanisms, abiotic changes associated with elevation altered the outcome
 of an ant-aphid protection mutualism. To do so, we characterized the
 multi-trophic interactions among the ant Formica podzolica, the aphid
 Aphis varians, and aphid natural enemies occurring on the plant Chamerion
 angustifolium within replicate high and low elevation valleys. Low (vs.
 high) elevation sites had longer summers (snowmelt 13 days earlier) and
 were on average 1.1°C warmer and 41% drier throughout the year. At low
 elevations, individual ant colonies consumed approximately double the
 volume of carbohydrate baits, likely due to a higher foraging tempo, and
 possibly due to a greater demand for sugar- vs. protein-rich resources (as
 indicated by stable isotope analysis). Wild aphid colonies at low
 elevations were visited by 1.4-fold more natural enemies (controlling for
 variation in aphid abundance), while experimental aphid colonies on potted
 plants were tended 52% more frequently by ants. As a result, ants
 increased aphid colony survival by 66% at low elevations but had no
 detectable effect at high elevations; at low (vs. high) elevations aphid
 colonies without ants had lower survival, demonstrating stronger predator
 effects, while aphid colonies with ants had higher survival, demonstrating
 even stronger ant benefits. Analyses for the effects of mean summer
 temperature yielded qualitatively identical results to those based on
 elevation. Collectively, these findings support predictions for a greater
 sensitivity of higher trophic levels to warming and demonstrate how
 species interactions can vary across environmental gradients due to
 simultaneous changes in species traits and abundances across multiple
 trophic levels.
description: Site Climate
 VariablesLocation and climatic
 variables of each study site. Temperature and precipitation variables were
 estimated for 2009-2015 using the PRISM Climate Group Model, and day of
 year of first snowmelt was estimated using a regional regression (Petry et
 al. 2016).SiteClimVars.csvAnt Abundance DataThe abundance of Formica podzolica ants collected in pitfall traps in high and low elevation sites both in 2012 and 2015.AntAbundance.csvAnt Mound Size and Activity DataThe size and activity of focal high and low elevation Formica podzolica ant nest mounds.MoundSizeActivity.csvAnt Abundance and Colony Activity R codeThis is the R script for analyses of ant abundance and colony activity.Ant Stable Isotope DataStable isotopes of Formica podzolica adults and pupae collected from focal high and low elevation ant nest mounds.AntStableIsotopes.csvAnt Stable Isotope R CodeThis is the R script for analyses of ant diet as indicated by stable isotope analysis.Bait Consumption DataFormica podzolica ant carbohydrate consumption as indicated by recruitment to baits.BaitConsumption.csvBait Consumption R codeThis is the R script for analyses of ant carbohydrate consumption as indicated by recruitment to baits.Ant Effects on Aphids DataFormica podzolica ant effects on experimentally established colonies of the aphid Aphis varians feeding on Chamerion angustifolium at high and low elevations.AntEffectsOnAphids.csvAnt Effects on Aphids R CodeThis is the R script for analyses of the effects of ants on aphids.Natural Enemy Abundance DataThe abundance of aphid natural enemies on focal Chamerion angustifolium plants in one high (East River Valley) and one low elevation valley (Spring Creek) in 2009.NaturalEnemyAbundance.csvNatural Enemy Abundance R CodeThis is the R script for analyses of natural enemy abundance.README fileThis file contains descriptions of all data files and R scripts.