A Generalizable Tool for Predicting Developmental Phenology for Wild Ecotherms

ABSTRACT

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.