DOI: 10.5061/dryad.k98sf7m43
title: Data from: Temperature-driven colour lightness and body size variation scale to local assemblages of European Odonata but are modified by propensity for dispersal

description: Previous macrophysiological studies suggested that temperature-driven
 colour lightness and body size variations strongly influence
 biogeographical patterns in ectotherms. However, these trait-environment
 relationships scale to local assemblages and the extent to which they can
 be modified by dispersal remains largely unexplored. We test whether the
 predictions of the thermal melanism hypothesis and the Bergmann’s rule
 hold for local assemblages. We also assess whether these trait-environment
 relationships are more important for species adapted to less stable
 (lentic) habitats, due to their greater dispersal propensity compared to
 those adapted to stable (lotic) habitats. We quantified the colour
 lightness and body volume of 99 European dragon- and damselflies (Odonata)
 and combined these trait information with survey data for 518 local
 assemblages across Europe. Based on this continent-wide yet spatially
 explicit dataset, we tested for effects temperature and precipitation on
 the colour lightness and body volume of local assemblages and assessed
 differences in their relative importance and strength between lentic and
 lotic assemblages, while accounting for spatial and phylogenetic
 autocorrelation. The colour lightness of assemblages of odonates increased
 and body size decreased with increasing temperature. Trait-environment
 relationships in the average and phylogenetic predicted component were
 equally important for assemblages of both habitat types but were stronger
 in lentic assemblages when accounting for phylogenetic autocorrelation.
 Our results show that the mechanism underlying colour lightness and body
 size variations scale to local assemblages, indicating their general
 importance. These mechanisms were of equal evolutionary significance for
 lentic and lotic species, but higher dispersal ability seems to enable
 lentic species to cope better with historical climatic changes. The
 documented differences between lentic and lotic assemblages also highlight
 the importance of integrating interactions of thermal adaptations with
 proxies of the dispersal ability of species into trait-based models, for
 improving our understanding of climate-driven biological responses.
description: We compiled from literature, extensive Information on water body
 location and type (i.e. <b>habitat</b>; lentic or lotic) and
 the composition of local assemblages of Odonata (dragonflies and
 damselflies) across Europe. This included a distribution data of 5,703
 records of 99 species occurring in 518 local assemblages across 28
 European countries. We calculated the average colour
 lightness (<b>colour lightness</b>) and body volume
 (<b>body volume</b>) of species using scanned (24-bits, sRGB,
 1200 dpi resolution) drawings of the dorsal body surfaces of European
 Odonata. We cropped out the body (head, abdomen, and thorax) using
 functions of Adobe Photoshop CS2. Based on these images the average colour
 of the pixels of an image across the red, green and blue channels was
 calculated as an estimate of the colour lightness of a species (8-bit grey
 values ranging from 0: absolute black to 255: pure white). We also scaled
 the images with the magnification factor provided by its source and used
 that to calculate body volume in cm<sup>3</sup> (π × [½ length
 of pixel row]<sup>2</sup> × pixel edge length) as an estimate
 of the body size of a species based on the assumption that odonates
 generally have a cylindrical body form. The calculations were performed
 using functions of the R-package <i>png.</i> We then averaged
 the colour lightness and body volume values across the species
 (<b>sp_rich</b>) of each local assemblage.
 We extracted 19 commonly used bioclimatic variables from
 Chelsa-climate.org based on geographical coordinates
 (<b>lat</b><i>, </i><b>lng</b>) of the
 assemblages (with a buffer radius of approximately 1 km) with a resolution
 of 2.5 arcminutes. After a principal component analysis of all 19
 bioclimatic variables (e.g. <b>PC_t1</b>), we considered only
 annual mean temperature and annual precipitation (<b>bio1</b>
 and <b>bio12</b>, respectively) since they contributed
 strongly to the overall trends in temperature and precipitation.