DOI: 10.5061/dryad.crjdfn31r
title: Data from: Testing trade-offs and the dominance-impoverishment rule among ant communities

description: Aim: Ant communities are believed to be structured by competition, with
 dominant species competitively excluding subordinates (the
 dominance-impoverishment rule). However, a high number of seemingly
 similar species coexist, possibly due to interspecific trade-offs. Here,
 we examine the evidence for the dominance-impoverishment rule across a
 broad latitudinal gradient and explore whether trade-offs explain
 coexistence within and among ant communities. Location: 40 sites in 19
 countries across Europe, western North America and northern South America.
 Taxon: Formicidae. Methods: We conducted 2-h baiting experiments at each
 site. Three dominance scores were calculated for each species at each site
 where it occurred. We then examined the relationship between ant dominance
 and diversity and tested for the generality of three trade-offs
 (dominance-discovery, dominance-thermal tolerance and
 dominance-generalism) within and among ant communities along with the
 possible effects of environmental variables on these trade-offs. Results:
 We found no support for the dominance-impoverishment rule. Instead,
 overall species richness at baits was positively correlated with the
 number of dominant species and exhibited a unimodal relationship with the
 relative abundance of dominant ants. Moreover, we found little consistent
 evidence for the three interspecific trade-offs. Main conclusion: Although
 total species richness at baits is positively correlated with species
 richness of dominant species and, to a point, increasing worker numbers of
 dominants, trade-offs among species do not appear to shape broad-scale
 patterns of coexistence among ants. Species richness declines only when
 the numbers of dominant workers are very high. Together, these results
 suggest that while trade-offs and the dominance impoverishment rule might
 promote coexistence or shape ant communities in some locations, the
 evidence for their being general across communities is scant.
description: We conducted baiting experiments at 40 sites of 20 x 20 m (each
 consisting of four 5 x 5 m subplots) during the daytime between June
 29<sup>th</sup> and November 11<sup>th</sup> 2016
 at 40 sites: 20 in Spain, seven in France, five in Germany, three in
 Denmark, four in the United States, and one in French Guiana (Fig. 1).
 Sites were in areas with known ant activity or where ant fieldwork had
 previously been carried out and spanned a range of ecological biomes,
 including temperate forests, deserts and xeric shrublands and rainforests.
 Sites were separated by at least 100 m. We designed the experiments
 similarly to classic experiments in ant ecology (Fellers, 1987; Savolainen
 & Vepsalainen, 1988; Savolainen, Vepsäläinen &
 Wuorenrinne, 1989; Andersen, 1992; Perfecto, 1994; Cerdá et al. 1997;
 Sanders & Gordon, 2003). Specifically, we chose five different
 resources (canned tuna in water, untoasted sesame seeds, 20 % sugar water
 solution, 1 % saltwater solution and tap water) to attract diverse species
 at each site. Approximately one teaspoon of solid resources and 2.5 cm
 diameter cotton balls soaked in the liquid resources were placed on
 individual ~6 cm diameter plastic discs in the middle of each subplot in a
 pentagonal shape, equidistant from the plot boundaries and approximately
 20 cm from each other. Twenty baits were deployed at each site: One bait
 per bait type (5) per subplot (4). After deploying the baits, the numbers
 and identities of ants present were recorded after 5, 15, 30, 60, 90 and
 120 minutes. Ground temperatures were measured during each observation
 using a handheld infrared thermometer (Raytek Raynger ST). Ants were
 identified to species or morpho-species either in the field or in the
 lab.  We extracted four environmental variables from
 online databases for each site. Mean annual temperature (MAT) and annual
 precipitation (AP) data were extracted from the 1970-2000 average
 WorldClim2 dataset at a resolution of 30 arc seconds (Fick &
 Hijmans, 2017). We extracted monthly normalised difference vegetation
 index (NDVI) values for each site during the month when sampling occurred
 from Moderate-Resolution Imaging Spectroradiometer MOD17, 30-arcsec data
 (Didan, 2015). We estimated actual evapotranspiration (AET) using Turc’s
 formula (Turc, 1954; Kluge et al., 2006; Sanders, Dunn, Fitzpatrick,
 Carlton, Pogue, Parker & Simons, 2009), where AET = P/[0.9 + (
 P/L)<sup>2</sup>]<sup>1/2</sup> with L = 300 + 25T
 + 0.05T<sup>3</sup>, P = annual precipitation and T = annual
 mean temperature.