1. Life histories, population dynamics and geographic range limits are fundamentally constrained by the way organisms acquire and allocate energy and matter. Metabolic theories provide general, parameter-sparse frameworks for understanding these constraints. However, they require the accurate estimation of body temperature which can be especially challenging in terrestrial environments.
2. Here, I integrate a metabolic theory (Dynamic Energy Budget theory, DEB) with a biophysical model for inferring field body temperatures and activity periods of terrestrial ectotherms and apply it to study life-history variation and geographic range limits in a widespread North American lizard, Sceloporus undulatus.
3. The model successfully predicted trait co-variation (size at maturity, maximum size, reproductive output and length-mass allometry) through changes in a single parameter. It also predicted seasonal and geographic variation in field growth rates, age at first reproduction, reproductive output and geographic range limits (via rmax estimates), all as a function of spatial climatic data. Although variation in age at maturity was mostly explained by climate, variation in annual reproduction was largely a product of local body size.
4. Dynamic Energy Budget metabolic theory is concluded to be a powerful and general means to mechanistically integrate the dynamics of growth and reproduction into niche models of ectotherms.