DOI: 10.5061/dryad.j6kn128
title: Data from: Elevational cline in herbivore abundance driven by a monotonic increase in trophic level sensitivity to aridity

description: 1. The abiotic environment drives species abundances and distributions
 both directly and indirectly through effects on multi-trophic species
 interactions. However, few studies have documented the individual and
 combined consequences of these direct and indirect effects. 2. We studied
 an ant-tended aphid along an elevational gradient, where lower elevations
 were more arid. Hypotheses of stronger species interactions at lower
 elevations and a greater sensitivity of higher trophic levels to climate
 led us to predict increased top-down control of aphids by natural enemies
 (third trophic level) but even stronger protection from mutualist ants
 (fourth trophic level) with increasing aridity. As a result, we predicted
 that mutualism strength and aphid abundance would increase with aridity.
 3. We documented patterns of aphid abundance and tested for both the
 direct and multi-trophic indirect effects of aridity on aphid performance.
 To do so, we used both observational and manipulative methods across two
 years in replicate high and low elevation valleys, where summer
 temperatures decreased by 3.7°C and precipitation increased by 27 mm/mo
 from low to high elevations. 4. Aphid colonies were 75% larger in the most
 (vs. least) arid sites, and this was best explained by changes in
 interactions with predators and ants. Aphids were unaffected by the direct
 effects of the abiotic environment or its indirect effects via host plant
 quality. In contrast, natural enemy effects increased with aridity; under
 ant exclusion, natural enemies had no effect on aphids in the least arid
 sites but depressed colony growth by 252% in the most arid sites. Ant
 activity also increased with aridity, with ants discovering more aphid
 colonies and experimental baits and allocating more foragers per aphid,
 although there was no effect of aridity on ant abundance or community
 composition. Correspondingly, the mutualist services provided by ants
 increased with aridity; ants provided no benefits to aphids in the least
 arid sites but doubled colony growth in the most arid sites. 5. In
 summary, an elevational cline in herbivore abundance was driven by a
 monotonic increase in trophic level sensitivity to aridity. These findings
 illustrate that predicting species responses to climate change will
 require a multi-trophic perspective.
description: Climate
 DataLocation and climatic
 variables of each study site. Temperature and precipitation variables were
 estimated for 2012-2015 using the PRISM Climate Group Model, and day of
 year of first snowmelt was estimated using a regional regression (Petry et
 al. 2016).ClimData.csvClimate Data R CodeThis is the R script for analyses of the relationship between elevation and multiple climatic variables as well as the principal component analysis of these climatic variables. This R script uses the ClimData.csv data file.Aspen Canopy Surveys DataThe abundance of ants and aphids in aspen canopy surveys conducted in 2012.AspenCanopySurveys.csvAspen Canopy Surveys R CodeThis is the R script for analyses of aphid and ant abundance in aspen canopy surveys conducted in 2012. This script uses the AspenCanopySurveys.csv data file.Trophic Level Manipulations DataData describing interspecific interactions involving host plants, aphids, natural enemies, and ants in two, three, and four trophic levels treatments imposed in 2015.TrophicLevelManipulations.csvTrophic Level Manipulations R CodeThis is the R script for analyses of whether aridity mediated aphid performance directly and indirectly by altering aphid multi-trophic species interactions. This script uses the TrophicLevelManipulations.csv data file.Ant Abundance and Resource Use DataThe abundance of ants collected in pitfall traps in 2012 and 2015 as well as ant bait consumption in 2015.AntAbundanceResourceUse.csvAnt Taxonomic Composition in 2012 DataAnt taxonomic composition in pitfall traps in 2012.2012MultivariateData.csvAnt Taxonomic Composition in 2015 DataAnt taxonomic composition in pitfall traps in 2015.2015MultivariateData.csvAnt Abundance and Resource Use R CodeThis is the R script for analyses of ant abundance and taxonomic composition in pitfall traps as well as bait consumption. This script uses the AntAbundanceResourceUse.csv, 2012MultivariateData.csv, and 2015MultivariateData.csv data files.READMEThis file contains descriptions of all data files and R scripts.