Ontogenetic variation in thermal sensitivity shapes insect ecological responses to climate change

Insects have distinct life stages that can differ in their responses to environmental factors. We discuss empirical evidence and theoretical models for ontogenetic variation in thermal sensitivity and performance curves (TPCs). Data on lower thermal limits for development (T₀) demonstrate variation between stages within a species that is of comparable magnitude to variation among species; we illustrate the consequences of such ontogenetic variation for developmental responses to changing temperature. Ontogenetic variation in optimal temperatures and upper thermal limits has been reported in some systems, but current data are too limited to identify general patterns. The shapes of TPCs for different fitness components such as juvenile survival, adult fecundity, and generation time differ in characteristic ways, with important consequences for understanding fitness in varying thermal environments. We highlight a theoretical framework for incorporating ontogenetic variation into process-based models of population responses to seasonal variation and climate change.