DOI: 10.5061/dryad.hhmgqnkmg
title: Data for: Beyond latitude: Temperature, productivity, and thermal niche conservatism drive global body size variation in Odonata

description: Aim: So far, latitudinal body size-clines have been primarily discussed in
 the context of thermoregulation, sensu Bergmann. However, body size
 patterns are ambiguous in ectotherms and this heterogeneity remains poorly
 understood. We tested whether Bergmann’s rule and the resource
 availability rule which states that energetic requirements determine
 species’ body size, apply to damselflies and dragonflies (Odonata).
 Furthermore, we hypothesised that the contrasting effects of
 thermoregulation and resource availability (e.g. productivity) can obscure
 the overall gradient in body size variation. Location: Global Time period:
 Contemporary Major taxa studied: Odonata Methods: Using data for 43% of
 all odonate species described so far, we tested our hypotheses in
 phylogenetically and spatially comparative analyses at assemblage and
 species level. For the distribution data, we integrated expert range maps
 and ecoregional ranges based on all available occurrence records. To
 distinguish between long-term versus evolutionarily recent responses of
 environmental drivers in body size, we constructed a phylogenetically
 informed classification of all odonate species and decomposed the body
 size into its phylogenetic and specific component for our subset of
 species. Results: We documented a weak positive relationship between body
 length and latitude but found strong and contrasting effects for
 temperature between dragonflies and damselflies and consistent positive
 effects for productivity that explained 35%–57% of body size variation.
 Moreover, we showed a strong phylogenetic signal in sized-based
 thermoregulation that shaped the distribution of dragonflies, but not of
 damselflies. Main conclusion: We concluded that temperature, productivity,
 and conservatism in size-based thermoregulation synergistically determine
 the distribution of ectotherms, while the taxon-specific importance of
 these factors can lead to contrasting results and weak latitude–size
 relationships. Our results reinforce the importance of body size as a
 determinant of species distributions and responses to climate change.
description: For our main analysis, we
 combined three types of information.
 1) Body
 size We
 compiled body size data from measurements of museum specimens and from the
 literature for 2,802 odonate species worldwide. For the main analyses, we
 used only data of body length for adult male individuals but mobilized
 other proxies of body size if available for imputation of the body length
 and supplementary analysis of body shape differences between Anisoptera
 and Zygoptera. Specifically, we measured the body and hindwing length
 (excluding terminal appendages) from images of 724 individuals of African
 odonates provided by the Naturalis Biodiversity Center (RHNM, Leiden, The
 Netherlands) and 487 specimens of African species from the Senckenberg
 Natural History Museum (SNHM, Frankfurt, Germany). For the images of
 African species from the Naturalis Biodiversity Center, European species
 from Dijkstra and Lewington (2006), and North American species from
 Needham et al. (2000), we calculated the body length, hindwing length, and
 body area as previously described (Pinkert et al. 2017; Zeuss et al. 2017)
 using the R-package ‘png’ (Urbanek 2013). In short, the number of pixels
 of the body from the head to the distal end of the abdomen, that of the
 hindwing from its base to the tip, and the number of all pixels of the
 body were calculated. The pixel estimates were transformed to metric units
 through the product of the scale (provided or measured on the images) and
 image resolution. The body area and body length data from image-based
 measurements of 1,146 individuals were used to test for the difference in
 the body shape of both suborders. 3,612 additional length measurements were
 extracted from species descriptions provided in 19 literature and 2
 internet sources (Table S1). Because of sexual dimorphism, we did not use
 females in our study if measurements from literature differentiated
 between sexes. If sources reported descriptive body size statistics, we
 collected the minimum and maximum values to calculate means to aid the
 integration of data across sources. For 305 individuals, we predicted the
 body length from the provided hindwing length with a linear mixed effects
 model that included a random slope for genus nested in family and suborder
 (n = 810, conditional R<sup>2</sup> = 0.92). Finally, the
 5,128 individual measurement values (1909 singletons including those where
 only average values were provided) of 2,802 species were aggregated to
 average values of body length (‘body size’ hereafter) per
 species. Because of this very strong phylogenetic signal
 in the body size of odonates, we partitioned the total variance of average
 species body size into a phylogenetic and specific component, using
 Lynch’s comparative method (Lynch 1991) in the R-package ‘ape’ (Paradis et
 al. 2004). The different aspects of body size variation in species-level,
 as well as assemblage-level analyses (i.e. averaged across species
 co-occurring within a 100 km × 100 km grid cell), are named ‘BL_mean’
 (unpartitioned), ‘P’, and ‘S’, respectively. The P component represents
 the variation in body size predicted by the phylogenetic relationships
 between species. The S component represents residuals from these
 predictions and hence the species-specific deviation from the
 phylogenetically predicted part.   2) Distribution data
 We combined two types of
 distributional information: expert range maps and ranges derived from
 intersections of occurrence records with the terrestrial ecoregions of the
 world. We downloaded expert range maps from IUCN.org (IUCN 2021) and
 digitised range maps that cover the entire ranges of European odonates
 from Boudot and Kalkman (2015). The data were taxonomically harmonised and
 intersected with grid cells of approximately 100 km × 100 km (military
 grid reference system [mgrs]). However, many of the IUCN range maps were
 incomplete or were delineated by political borders instead of factual
 species ranges (Hughes et al. 2021). Except for the range maps from Boudot
 and Kalkman (2015), we used ecoregional ranges to extend and complete the
 dataset characterizing the distribution (Pinkert et al.
 2022a). 3) Environmental data
 To investigate the
 environmental drivers of body size variation in Odonata assemblages, we
 used two variables associated with geographic patterns of temperature
 (mean annual temperature [‘Bio_1’] and elevation [‘Elev’]) along with the
 enhanced vegetation index (‘Annual_EVI’) as a proxy for productivity. The
 data were downloaded from the CHELSA (Karger et al. 2017, 2018;
 chelsa.org, current condition records) and EarthEnv (Amatulli et al. 2018)
 databases. The EVI layer was cropped to the extent of the climate
 variables (1 km × 1 km). For our main analyses, these data were
 aggregated(averaged) to the assemblage level. In addition to the trait and
 environmental data, the dataset included coordinates of the centroid of
 each grid cell. For detailed methods and further descriptions see Mähn et
 al. (Beyond latitude: Temperature, productivity, and thermal niche
 conservatism drive global body size variation in
 Odonata).