| Current survival can be affected by the previous conditions experienced including food availability, stressful environmental conditions, and behavioral interactions with other individuals. In this dissertation, I explored relationships between various types of prior experiences and current survival capacities of fishes in experiments that help answer broad ecological questions and assess mitigation strategies in applied sciences. In Chapter 2, I determined that competition-induced heterogeneity among individuals can increase survival at the population level by challenging a model fish species, guppies ( Poecilia reticulata), that had been reared at various levels of food availabilities and presence or absence of competition, to increased water temperature and in the absence of food. In Chapter 3, I revealed that two types of lethal stress occurring at different time scales can result in episodes of selection and a step-like pattern in the survival curves of juvenile hatchery rainbow trout (Oncorhynchus mykiss). In Chapter 4, the mitigation strategy of the Juvenile Fish Transportation Program in the Federal Columbia River Power System (Washington and Oregon) was assessed by examining the relative survival capacities (or vitality) of run-of-river and barged hatchery spring/summer Chinook salmon (O. tshawytscha) collected immediately after passage through the hydropower system. In general, the water temperature previously experienced was different between ROR and barged fish, and showed the greatest influence on survival capacities. In Chapter 5, I determined critical thresholds of simple physical condition indices in Coho salmon (O. kisutch) and investigated whether skewed distributions of condition indices for these fish can be used as an indicator of a population experiencing lethal stressors (increased water temperature and absence of food). Although survival can be complex to investigate because of the many processes occurring across different dimensions (e.g. temporal scale, heterogeneity, and skewness) and different biological levels (e.g. subcellular, cellular, individual, and population), my challenge experiments were a relatively simple method to investigate processes underlying survival patterns, and helped show the importance of cumulative effects on survival. |
