Beyond temperature: Relative humidity systematically shifts the temperature dependence of population growth in a malaria vector

Understanding ectotherm responses to environmental change is central to coping with many of humanity’s current and future challenges in public health, biodiversity conservation, and food security. Complex relationships between abiotic and biotic factors can influence ectotherm abundance and distribution patterns by introducing stage–specific variation in fitness trait responses. Variation in temperature, rainfall, competition, and habitat have all been considered in previous attempts to understand how environmental factors can interact and vary in their relative influence on species’ maximal population growth rates, r _m . However, the combined effects of temperature and humidity on this fundamental metric are poorly understood. We show that variation in relative humidity can influence juvenile trait responses and r _m ’s temperature dependence in Anopheles stephensi , an important malaria vector. Our climate suitability maps show that the interactive effects of temperature × humidity on juvenile traits have important implications for predicting how environmental change will influence arthropod–mediated systems.