Heat wave impacts across scales in the splash pool copepod, Tigriopus californicus

Temperature influences biological processes at all levels of biological organization. As such, temperature is a fundamental abiotic variable affecting ectotherm fitness. As human induced climate change persists, the need to understand biological responses to temperature has never been more pressing. One consequence of rapid climate change is an increase in the frequency and intensity of heat waves. Despite substantial interest in the physiological effects of heat stress, it is less clear how individual responses to extreme heat events influence population-level responses such as persistence and population growth. Energy balance is a unifying concept that integrates the effect of temperature across scales. The Energy Limited Tolerance to Stress (ELTOS) framework links physiological models of temperature and oxygen availability to dynamic energy budgets in order to predict the effect of stress on individual reproduction and population growth. Drawing on the ELTOS framework, I tested three critical predictions about individual thermal experience, and how the influence of heat stress scales up from physiological to individual to populations, utilizing the splash pool copepod, Tigriopus californicus. In Chapter 2, I tested the prediction that aerobic energy production declines with increasing heat wave intensity and duration, and that individual reproduction declines similarly. In Chapter 3, I tested the assumption that short-term impacts of heat waves on individual reproduction have persistent effects on longer-term population dynamics. In Chapter 4, I tested for an effect of spatial variation in thermal history on subsequent heat wave survival. Together, these tests provide a comprehensive examination of ELTOS predictions of biological responses to heat waves across scales. My data are consistent with ELTOS predictions that heat wave intensity affects energy balance and subsequent individual reproductive effort. However, I did not find consistent patterns of population dynamics over both short and longer-term time scales. The opposing effect of temperature on different life-history traits that occur over different time-scales likely underlies differences in the effect of short-term heat wave effects on population dynamics over short and longer time periods. Lastly, I found that spatial variation in thermal history, particularly recent heat accumulation, explains reduced survivorship during experimental heat waves.Science, Faculty ofZoology, Department ofGraduat