Tomas C. O'Keefe

Advisor: Dr. Stanley Dodson

Ph.D Zoology, 2002: Spatial and Temporal Patterns in Aquatic Ecosystems: Three Case Studies.

A central goal of aquatic ecology is understanding the factors that affect the relationships, distribution, and abundance of organisms in aquatic ecosystems. Freshwater ecosystems integrate the effects occurring within the water, the surrounding landscape, and the entire globe. These freshwater systems have importance for both the environment and guman society as they provide numerous ecosystem and societal services. Using different techniques and approaches, I examined questions from three areas of freshwater ecology that are critical to our understanding of ecosystem functions that aquatic habitats provide. Each chapter takes advantage of natural variation in the environment and a long-term perspective to address questions of ecosystem and community ecology at different scales. The chapters characterize the development and maintenance of spatial and temporal patterns, and the ecological consequences of these patterns for system dynamics. The first study deals with zooplankton population dynamics in six lakes from the Northern Temperate Lakes LTER program. I found that in general zooplankton species display unique patterns or no distinct pattern in their population dynamics among different lakes. Population dynamics are likely primarily structured by internal processes unique to each lake. The second study examines the diet of smallmouth bass and yellow perch in Nebish Lake, WI and documents ontogenetic niche shifts that may affect interaction among the two species. This study illustrates the fact that although perch may serve as prey for smallmouth bass, the two species may be competing particularly during the first year of life. Furthermore diet data showed strong evidence for benthic-pelagic coupling. In the final chapter I explored the potential for the importance of salmon nutrient subsidies to vary across watersheds with a range of alder coverage. I show that aler can make an important and significant contribution to the nitrogen pool in aquatic systems. While the nutrient contribution from salmon is clearly important, it must be considered in the borader ecosystem and landscape context. These topics represent different approaches and scales that are necessary for insight into the function of aquatic ecosystems.