DOI: 10.5061/dryad.d7wm37q4f
title: Community-wide trait adaptation, but not plasticity, explain ant community structure in extreme environments

description: 1. Quantifying trait-environment associations can help elucidate the
 processes underpinning the structure of species assemblages. However, most
 work has focused on trait variation across rather than within species,
 meaning that processes operating at the intraspecific levels cannot be
 detected. Incorporating intraspecific trait variation in community-wide
 analyses can provide valuable insights about the role of morphological
 adaptation and plasticity on species persistence and the composition of
 ecological communities. 2. Here, we assessed geographic variation in the
 direction (i.e., adaptation) and strength of selection, and the magnitude
 of plasticity, by examining community-wide trait variation in ant
 communities along an environmental gradient spanning 9° latitude in
 Quebec, Canada. Specifically, we measured 9 morphological traits related
 to foraging strategies, resource use and thermal regulation at 20
 locations across temperate and boreal forests. We then examined how the
 mean and variance of these traits varied along temperature and
 precipitation gradients. Moreover, we examined how these trait-environment
 relationships varied across levels of organization, from individual
 workers (intraspecific) to colonies (intraspecific) and species
 (interspecific). 3. We observed changes in mean trait values along
 environmental gradients, but very little change in variance. Specifically,
 we observed a decrease in the mean length of antennae and an increase in
 the mean eye length from mild (warm and wet) to more extreme environments
 (cold and dry). These shifts in trait means were mostly coordinated across
 organizational levels (i.e., worker, colony, and species). We also
 observed a general increase in trait variance from mild to extreme
 environments, but only at the species level. 4. Our findings suggest that
 stressful environmental conditions exert a strong selection pressure on
 ant morphology causing shifts in optimal trait values. These adaptations
 may enable persistence at the northern edge of the boreal forest and
 therefore influence the composition of these ant communities.
 Specifically, ants with large eyes and short antennae are overrepresented
 at the transition zone between the boreal forest and the tundra, possibly
 representing an adaptation to these more open habitats. Our study
 demonstrates that combining spatial and community-wide intraspecific
 functional trait data provides a promising way forward to gain new
 insights on trait adaptations and processes underpinning community
 structure along environmental gradients.
description: We measured 9 morphological traits on 37 ant species found in 20
 sites along a 9° latitudinal gradient in Quebec, Canada. At each sampling
 site, we randomly established a 50×50 m plot. Within each corner and at
 the center of this plot, we placed a 10×10 m subplot. At each of these
 five subplots, we registered all soil and leaf-dwelling ant nests found by
 systematically searching in the leaf-litter, under rocks, dead trees and
 logs found within this area for 20 min (modified “Intensive sampling”
 technique described by Bestelmeyer et al., 2000). During this period, we
 put a flag where the colony was located and proceeded to continue our
 search. We only collected ant workers after this 20-min search period had
 ended. We collected a subset of at least 5-10 workers to sample.
 We measured nine raw morphological traits that are regularly used
 in the literature: (1) Body size (Weber's length), (2) pronotum
 width, (3) head length and (4) head width, (5) eye length and (6) eye
 width, (7) mandible length, (8) antenna (scape) length and (9) Femur
 length, following a standardized protocol suggested by Parr et al.
 (2017). At each site, we found between 1 to 24 colonies per species, and
 we measured all nine traits on 1 to 3 individual workers from each
 colony. for monomorphic species, we measured 1 to 3 specimens per colony.
 Then, for polymorphic species (e.g., Pheidole spp., Camponotus spp.), we
 visually selected and measured one representative of each size class
 (i.e., majors, intermediate and minors). We took standard linear
 measurements using an ocular micrometer mounted on a dissecting
 microscope, accurate to 0.01 mm. The macroenvironmental
 variables for each of the 20 sites: annual mean temperature and annual
 precipitation were extracted from WorldClim 2.0 (Fick & Hijmans,
 2017).
description: Please see "readme.txt" file for details of files.