Validating a low‐cost alternative to body surface area estimation: Implications for energy budgets and scaling relationships of ectotherms

Abstract The surface area of organisms is a key parameter in ecological and evolutionary applications. For example, surface area‐dependent traits such as rates of cutaneous water loss and of heat absorbed are relevant for predicting animal desiccation rates and body temperatures. Therefore, a general lack of surface area data and inaccurate scaling relationships can influence predictions of species' sensitivity to environmental change. In this study, we evaluate a portable, low‐cost, three‐dimensional (3D) structured light scanning approach to provide robust estimations of surface area of several lizard groups using museum specimens (20 species, 7 families). We validated this approach by comparing the surface areas of specimens to those obtained from 3D and micro‐computed tomography (μCT) scans of live individuals. The scaling of surface area obtained from 3D scans of museum specimens and live lizards was equivalent, supporting the usage of museum specimens. For a given body size, the surface area of live lizards from μCT scans was higher than those obtained from 3D structured light scans, likely due to the enhanced resolution of the former approach, but the scaling exponents did not differ. The scaling of surface area followed isometry for all species, except for three hypo‐allometric species relationships. The intercepts and scaling slopes of surface area differed more across than within families. A simulation using a widely employed surface area scaling based on geometric similarity (surface area = 10 Mass 2/3 ) yielded significantly different surface area estimates compared to those obtained from empirically based scaling relationships, influencing overall heat loads of lizards. This pattern was particularly acute with increased body size and higher direct solar radiation. Our results emphasize the need to obtain more robust surface area scaling relationships across lizard species and families, but also other taxonomic groups given the general paucity of these data. Our study demonstrates that 3D structured light scans of museum specimens are a practical, reliable and high throughput technique to achieve this objective, and we provide the methods and workflow to accomplish this task.