Direct and Indirect Temperature Pathways Decouple Growth and Development in a Headwater Stream Amphibian

The impacts of temperature on organism size have been proposed as the 3^rd major impact of climate change, after effects on species ranges and phenology. The underlying reason for this is the mechanism that underlies the temperature-size-rule (TSR); individuals that develop in warm temperatures are smaller at maturity (or any developmental stage transition) than those that develop in colder temperatures. While differences at a cellular or molecular level in how temperature affects the rates of growth (change in mass) and development (progression through life stages) are fundamental to the TSR, community-level or otherwise indirect temperature pathways are also at play. Due to the breadth of ecosystem components studied at the Trask paired watershed to understand forest management, we’re in a unique position to measure the roles of indirect temperature effects on growth and development rates and thereby put in perspective the direct plastic response to change in temperature. In this study we demonstrate the temperature-size-rule pattern for the headwater stream anuran Ascaphus truei. We then use structural equation modeling to measure the direct and indirect routes by which temperature differentially affects rates of growth and development using re-captures of individually marked tadpoles among 18 streams over four years.