I investigated the spatiotemporal dynamics of plant communities on islands in the Aleutian archipelago, Alaska, using small scale plots and landscape level remote sensing. Islands of the Aleutian archipelago are a model system for vegetation studies: there is no significant variation in island size, geology, soil type, or plant composition for hundreds of islands spanning 1600km of longitude. There is variation in two important factors: nutrients and climate. Past fox introductions onto some of the islands substantially reduced seabird populations that formerly vectored nutrients from the sea to land. Previous field studies have documented significant differences in vegetation composition and biomass between fox­ infested and fox-free islands using small scale field measurements. I examined the landscape level vegetation response to nutrient subsidies on individual islands and to a regional climate gradient across the entire archipelago. There was also evidence of a climate gradient of gradual cooling from east to west. In order to capture the full extent of the spatial and temporal variation in the system, I developed a method of using high temporal frequency, moderate spatial resolution remote sensing data to measure the landscapes of entire islands across the archipelago through time. Using this technique I calculated the seasonal phenological profiles of every island, including descriptive parameters such as length, width, and peak of the growing season. With this information I was able to show that the plot level results scaled-up to the landscape level. I documented difference in the vegetation dynamics between nutrient subsidized and non-subsidized islands, demonstrating the landscape level impact of an apex predator. I also documented a regional cooling trend in climate and associated trends in vegetation dynamics. Overall, there was lower production from east to west on fox-infested islands. However, this longitudinal trend was not always present for the vegetation parameters on fox-free islands. This suggests that the significant nutrient subsidies can override the effect of climate in this system; a pattern that is driven by an introduced apex predator.

Juvenile fall-run Chinook salmon (Oncorhynchus tshawytscha) in the Sacramento-San Joaquin River Basin experience temporally and spatially heterogenous temperature regimes, between cool upper tributaries and the warm channelized Delta, during freshwater rearing and outmigration. Limited water resources necessitate human management of dam releases, allowing temperature modifications. The objective of this study was to examine the effect of temperature on specific dynamic action (SDA), or the metabolic cost associated with feeding and digestion, which is thought to represent a substantial portion of fish energy budgets. Measuring SDA with respect to absolute aerobic scope (AAS), estimated by the difference between maximum metabolic rate (MMR) and standard metabolic rate (SMR), provides a snapshot of its respective energy allocation. Fish were acclimated to 16°C, raised or lowered to each acute temperature (13°C, 16°C, 19°C, 22°C or 24°C), then fed a meal of commercial pellets weighing 2% of their wet mass. We detected a significant positive effect of temperature on SMR and MMR, but not on AAS. As expected, there was no significant effect of temperature on the total O₂ cost of digestion, but unlike other studies, we did not see a significant difference in duration, peak metabolic rate standardized to SMR, time to peak, percent of meal energy utilized, nor the ratio of peak O₂ consumption to SMR. Peak O₂ consumption represented 10.4-14.5% of AAS leaving a large amount of aerobic capacity available for other activities, and meal energy utilized for digestion ranged from 5.7% to 7.2%, leaving substantial remaining energy to potentially assimilate for growth. Our juvenile fall-run Chinook salmon exhibited thermal stability in their SDA response, which may play a role in maintaining homeostasis of digestive capability in a highly heterogeneous thermal environment where rapid growth is important for successful competition with conspecifics and for avoiding predation.

Juvenile salmonids migrate hundreds of kilometers from their natal streams to mature in the ocean. Throughout this migration, they respond to environmental cues such as local water velocities and other stimuli to direct and modulate their movements, often through heavily modified riverine and estuarine habitats. Management strategies in an uncertain future of climate change and altered land use regimes depend heavily on being able to reliably predict their ocean entry timings, route use, and survival rates through rivers and estuaries. We developed a spatially-explicit agent-based model of fish movement in response to hydrodynamic flows that uses movement dynamics gleaned from multi-dimensional tracking datasets of acoustically tagged juveniles moving through an urbanized, branched tidal estuary. We demonstrate how such models can be calibrated, and we apply it to the Sacramento-San Joaquin Delta in Central California. The quality of the out-of-sample validation of the model to predict juvenile salmon survival and route selection indicates that the model is versatile and flexible enough to be used in novel hydroclimatological conditions