Species diversity and environmental variability: patterns and processes of lacustrine fish community responses in a variable world

Thesis (Ph.D.)--University of Washington, 2015Ecosystems are heterogeneous on multiple scales of space and time, and this variation in abiotic and biotic features confronts organisms with complex challenges. Climate change signals are also often heterogeneous across these scales, and it is important to understand how climate plays out over the landscape due fine-scale variability in habitat. In addition, the temporal scale over which species respond to environmental change may vary across taxa, presenting an opportunity for mismatches in ecological relationships. To date, much work has focused on climate change effects on primary and secondary production in lakes, but mechanisms and community-level processes for higher trophic level organisms remain less clear. This dissertation aims to reveal patterns and processes of fish individual and community responses to environmental change on multiple time scales. In Chapter 1, I developed a bioenergetics model for the threespine stickleback to define ecological demands of this fish under a range of temperatures, indicating that this fish has a different thermal optimum than sympatric fishes. This physiological diversity has possible implications for community composition. Chapter 2 examined the intersection of seasonal variability and life history diversity, and showed that the timing of seasonal lake productivity varied widely across years and that sockeye salmon fry with more protracted migration experienced higher overall survival. Chapter 3 contributes to our understanding of how spatial variability can affect the way that fish communities change over time, and showed that, within a single lake, community change varied by fine-scale location and depended on species-specific responses to temperature. In Chapter 4, we asked how climate-driven changes in lakes can influence phenology and expression in a species trait. These results showed that reproduction in fish is closely linked to physical lake changes. As a whole this research illustrates that lacustrine fishes can be highly susceptible to changes in the environment. However, the responses that we observed depended upon physiological or life history diversity among and within species and diversity within habitats, and upon the scale at which changes are observed in the environment. My hope is that this dissertation will contribute to the understanding of the role of biological diversity in explaining ecosystem processes and observed changes to the environment