UC Santa Cruz

Individuals of the same species can vary dramatically in their size, physiology or behavior, thereby influencing their movement, growth and survival. Through influencing demographics individual variation is important to population resilience in the face of environmental change in space and time. Understanding the ecological consequences of individual and population variation is timely considering the dramatic rates of extinction and anthropogenic alterations we are witnessing including global climate change. Coastal rainbow trout (Oncorhynchus mykiss) express a dizzying range of variability in movement and growth rate. I used acoustic telemetry to determine the diversity of O. mykiss movement patterns in an altered river. Movement distance and frequency ranged widely from no movement over the 218d study period to traveling 170km to the Pacific Ocean in 14d. However, most individuals did not move more than 0.5km. Movement correlated with size, season and location. Mortality correlated with the number of moves rather than distance moved suggesting movement regardless of scale influenced survival. In laboratory experiments I found more northerly O. mykiss populations had growth optimals at colder temperatures than more southerly populations. However, temperature-dependent growth varied among populations at very local scales. Temperatures previously experienced did not affect temperature-dependent growth which is beneficial for a species that may experience dramatic fluctuations in temperature through space and time. I used a diet-switch experiment and model fitting to quantify the nitrogen isotope tissue turnover rate and discrimination factor for seven O. mykiss tissues. Among seven tissues, diet-tissue δ15N discrimination factors ranged from 1.3 to 3.4 /. Model supported tissue turnover half-lives ranged from 9.0 to 27.7 days. Using parameter estimates and their uncertainty, I developed stable isotope clocks to estimate the time since resource-shifts. A greater understanding of the extent and importance of individual and population-level variation in fundamental demographic (i.e. growth and survival) and life history (i.e. anadromy and thermal optima) parameters is key to the management and conservation of threatened species. This research revealed that O. mykiss populations vary in these fundamental parameters, implying the importance of local-scale management and conservation practices that ensure the continued diversity of these parameters within and among populations.