A Generalizable Tool for Predicting Developmental Phenology for Wild Ecotherms

Development in poikilothermic organisms is strongly temperature-dependent, particularly during early life stages prior to exogenous feeding. This thermally constrained physiology produces a near-mechanistic relationship between ambient temperature and developmental rate, allowing for predictive models of phenology. However, traditional models-often developed under constant laboratory temperatures-struggle to account for the variable thermal regimes experienced by wild populations. Effective value models were created to address this issue and are a framework that integrates diel temperature data to predict developmental timing under fluctuating conditions. Building on this foundation, the R package hatchR was developed for fishes to operationalize the effective value model and enable its widespread application. In this paper, we expand the scope of hatchR, demonstrating its applicability across a broad range of poikilothermic taxa including amphibians, reptiles, insects, crustaceans, copepods, and starfishes. We also illustrate how this framework supports both applied management goals-such as predicting hatching windows for conservation and monitoring-and basic research on ecological and evolutionary questions including phenological plasticity, thermal adaptation, and ecological interactions. By providing a generalizable, open-source tool, hatchR bridges the gap between physiological theory and real-world application, offering a robust platform for predicting developmental phenology in diverse and changing environments.