J.F. Gillooly

Advisor: Dr. Stanley Dodson

Ph.D. Zoology, 1999: The combined effects of temperature and body size on the life histories and ecology of aquatic ectotherms.

I begin this dissertation in Chapter 1 by establishing the relationship of embryonic development time to egg size for zooplankton, fishes and amphibians at different constant temperatures (5, 10, 15, and 20 C). In Chapter 2, I describe this relationship for univoltine and multivoltine aquatic insects at 10, 15, 20, and 25 C. Expressed in terms of degree-days, the relationship of egg size to embryonic development time was similar in slope and intercept for most aquatic ectotherms across temperatures. Univoltine aquatic insects, however, required nearly 3 times longer to develop than other ectotherms of similar egg size. In Chapter 3, I defined the relationship of postembryonic development time to adult mass across temperatures for zooplankton. This permitted me to express the proportion of generation time spent in emryonic versus postembryonic development as a function of relative egg size (egg size/body size) for zooplankton at different temperatures.

In Chapters 4-6, I describe patterns in the community structure of zooplankton, fishes and amphibians that may be explained by the size-dependent temperature effects on development time presented in Chapters 1-3. In Chapter 4, I describe latitudinal patterns in cladoceran body size and Daphnia seasonal dynamics related to water temperature. In Chapter 5, I consider how differences in zooplankton development time related to body size alter the interpretation of the effects of size-selective fish predation on zooplankton communities. In Chapter 6, I show that spawning date is negatively related to egg size, similarly for both amphibians and fishes.

Together, the relationships of development time to body size and temperature presented in Chapters 1-3 provide a new framework within which to interpret the behavior, ecology and evolution of aquatic ectotherms. The patterns in the behavior and ecology of zooplankton, fishes and amphibians presented in Chapters 4-6 are examples of how these relationships help explain the structure of aquatic communities. In short, in this dissertation, I show that patterns as diverse as the date of spawning in fishes, and the date of maximum Daphnia abundance in a lake, are related to the effects of body size and temperature on development time.