DOI: 10.5061/dryad.kh1893243
title: Multidimensional trait morphology predicts ecology across ant lineages

description: 1. Understanding the link between ecology and morphology is a fundamental
 goal in biology. Ants are diverse terrestrial organisms, known to exhibit
 ecologically-driven morphological variation. While relationships between
 individual traits and ecologies have been identified, multidimensional
 interactions among traits and their cumulative predictive power remain
 unknown. Because selective pressures may generate convergent syndromes
 spanning multiple traits, we applied multivariate analyses across a wide
 sampling of taxa to assess ecomorphological variation in an integrative
 context. 2. How well does morphology predict ecology? Moreover, are there
 quantitatively-supported ant ecomorphs? We investigated the links between
 trait morphology and ecology by assembling a morphometric dataset spanning
 over 160 species within 110 genera. Because ants occupy a wide range of
 ecologies, we compiled natural history data on nesting microhabitat,
 foraging stratum, and functional role into 35 defined niche combinations.
 This tripartite ecological classification and our morphological dataset
 were optimized under dimension reduction techniques including Principal
 Component Analysis, Principal Coordinate Analysis, Linear Discriminant
 Analysis, and Random Forest supervised machine learning. 3. Our results
 describe ant ecomorphospace as comprising regions of shared, generalized
 morphology as well as unique phenotypic space associated with specialized
 ecologies. Dimension reduction and model-based approaches predict ecology
 with 77-85% accuracy and Random Forest analysis consistently outperforms
 LDA. While accounting for shared ancestry, we found eye, antennal scape,
 and leg morphology to be most informative in differentiating among
 ecologies. We also note some heterogeneity between trait significance in
 each ecological aspect (nesting niche, foraging niche, functional role).
 To increase the utility of ecomorphological classification we simplified
 our 35 observed niche combinations into 10 ecomorph syndromes, which were
 also predicted by morphology. The predictive power of these machine
 learning methods underscores the strong role that ecology has in
 convergently shaping overall body plan morphology across ant lineages. We
 include a pipeline for predictive ecomorphological modeling using
 morphometric data, which may be expanded with additional specimen-based
 and natural history data.
description: Our dataset includes ant trait measurements from 15 subfamilies, 113 genera, and 167 species, with associated ecological niche information. Morphometric sampling included linear measurements of 12 cephalic traits and 5 post-cephalic traits, with 5 additional traits that were not subsequently included in our analyses but are presented here, after preliminary analyses indicated overlap with other metrics, variation due to measurement artifacts, or lack of significance across all niche aspects. Fifteen selected traits have been previously correlated with ecology. All measurements were conducted on point-mounted specimens under stereo microscopy. Including raw measurements in dimension reduction techniques such as principal component analysis can result in body size driving the overwhelming majority of variation in a dataset, masking other potentially important contributors. To explore the impact of body size, we created two datasets for analyses: a dataset comprising raw measurements and a size-corrected dataset using only ratios. Tab 1 (all data (raw measurements)) is the raw measurements dataset; tab 2 (all data (ratio measurements)) is the size-corrected ratios dataset; tab 3 (tree-matched data (raw meas.)) holds a dataset of raw measurements pruned to taxa that are included in Blanchard and Moreau's 2017 comprehensive ant phylogeny to facilitate phylogenetic corrections; tab 4 (tree-matched data (ratio meas.)) includes the same taxa as in tab 3 but with the size-corrected ratio measurements. 
description: All measurements included here are in millimetres.
 Raw trait measurement definitions are as follows: head_width is
 the width of the head at the broadest point in frontal view; head_length
 is the length of the head at the longest point in frontal view;
 webers_length is the length of the mesosoma from the anterodorsal margin
 of the pronotum to the posteroventral margin of the mesosoma;
 procoxal_length is the length of the procoxa in lateral view; eye_length
 is the maximum length of the eye; tarsal_claw_length is the maximum length
 of the tarsal claw; tarsal_claw_width is the maximum width of the tarsal
 claw; mesosoma_height is the height of the mesosoma taken at a right angle
 to Weber's length; mandible_length_profile is the length of the
 mandible from insertion point to apical tooth in lateral view;
 mandible_angle is the angle between the plane of the mandible and plane of
 the head capsule; eye_height_total is the maximum total height of the head
 capsule; eye_height_dorsal is the height of the head from the midpoint of
 the eye to the dorsal margin of the head capsule; eye_height_ventral is
 the height of the head from the midpoint of the eye to the ventral margin
 of the head capsule; eye_length_total is the total length of the head in
 lateral view; eye_length_anterior is the length of the head from the
 midpoint of the eye to the anterior clypeal margin; eye_length_posterior
 is the length of the head from the midpoint of the eye to the posterior
 margin of the head capsule; mandible_length_face is the length of the
 mandible from insertion point to apical tooth in frontal view;
 metafemur_length is the maximum length of the metafemur; scape_length is
 the maximum length of the scape; ventral_head_length is the maximum length
 of the head along the ventral margin; ventral_pronotal_length is the
 maximum length of the prothorax along the ventral margin; pronotal_width
 is the width of the pronotum at the broadest point in dorsal
 view.  Ratio trait measurement definitions are as
 follows: head_shape is the head width divided by head length;
 procoxal_ratio is the procoxal length divided by Weber's length;
 eye_head_size is the eye length divided by the head length; thorax_shape
 is the pronotal width divided by Weber's length; pronotal_shape is
 the pronotal width divided by the mesosoma height; mandible_curvature is
 the mandible length in lateral view divided by the mandible length in
 frontal view; mandible_head_length is the mandible length in lateral view
 divided by the head length; eye_dorsoventral is the fraction of the head
 capsule from the dorsal margin to the midpoint of the eye divided by the
 total height of the head; eye_anteroposterior is the fraction of the head
 capsule from the anterior clypeal margin to the midpoint of the eye
 divided by the head length in lateral view; scape_proportion is the length
 of the scape divided by the head length; metafemur_proportion is the
 length of the metafemur divided by Weber's length; mesosoma_shape is
 the height of the mesosoma divided by Weber's length.
 Functional role binning definitions in the "func_role"
 column are as follows: GP represents generalist predators with broad
 taxonomic diets; SP represents specialist predators with obligate feeding
 on a specific taxon; Om represents omnivores with broadly ranging diets;
 Py represents phytophagous feeding such as extrafloral nectaries and
 herbivory; Fg represents fungus-growing/farming; Tr represents
 trophobiotic relationships with other insects; Gn represents granivory; Mh
 represents mushroom-foraging.  Nesting niche binning
 definitions in the "nest_niche" column are as follows: Cn
 represents carton-nesting or forming structured nests from plant material
 in trees and shrubs; Gr represents ground-nesting in dirt mounds, under
 stones, rock cracks, etc.; Lg represents lignicolous nesting or nesting in
 twig and tree cavities; Ll represents leaf litter-nesting in leaf litter
 interstitial spaces; Sb represents subterranean nesting entirely
 underground.  Foraging niche binning definitions in the
 "forag_niche" column are as follows: Ab represents arboreal
 foraging in and on trees and shrubs; CR represents column-raiding
 behaviour that may be cooperative, nomadic, or raiding predation; Eg
 represents epigaeic foraging on the ground surface; Ll represents leaf
 litter foraging within leaf litter interstitial spaces; Sb represents
 subterranean foraging underground.  Ecomorph syndrome
 definitions in the "ecomorph" column are as follows: om_grll_eg
 represents ground- or leaf litter-nesting epigaeic omnivores; om_leaf
 represents leaf litter omnivores; om_lg_ab represents lignicolous arboreal
 omnivores; om_cn_ab represents carton-nesting arboreal omnivores; om_sub
 represents subterranean omnivores; pred_gr_egll represents ground-nesting
 epigaeic or leaf litter predators; pred_leaf represents leaf litter
 predators; pred_lg_ab represents lignicolous arboreal predators; pred_cr
 represents column-raiding predators; pred_ll_g represents leaf
 litter-nesting epigaeic predators; pred_sub represents subterranean
 predators.  Other notes: the "PGLS_data"
 column in the "all data (raw measurements)" tab indicates which
 taxa match the Blanchard and Moreau 2017 phylogeny for further
 phylogenetic corrections; the "ecology_ref" column indicates
 references for the ecological niche information for that taxon. Taxa that
 are identified to genus and subsequent morphospecies are denoted by _sp1,
 _sp2, etc.; instances where taxonomic identification was not entirely
 certain are denoted with a _cf.