The Maintenance and Generation of Freshwater Diversity from the Local to the Global Scale

The distribution of biological diversity is markedly uneven across the world. Despite the seemingly endless variety of forms and adaptations that have evolved and continue to evolve, large differences in the numbers and characteristics of species remain among locales. These differences are often not random; e.g., the Earth's tropics are disproportionately rich in the diversity of life and large areas harbor more species than small areas. Observations of these general biogeographic patterns are some of the oldest contributions by early naturalists and ecologists, yet explanations for these patterns are a recurring topic of debate. Generality of pattern (with room for exceptions to the rule) has been reached for large-scale gradients in diversity but not generality of the theories that underlie these patterns.;Unlike diversity at the biogeographic scale, even the generality of pattern at the local scale of species interactions remains elusive. Although numerous investigations into how potential drivers of local diversity such as productivity, isolation, and disturbance influence diversity have been made, a unifying consensus to describe general patterns of local diversity has not emerged. Today, increasing emphasis is being placed on the importance of the interaction between local and regional scales in influencing local diversity.;The thesis first introduces and summarizes attempts to describe and explain biodiversity patterns at both the local and regional scales. Chapter 1 describes a study of the role of dispersal and assembly history in influencing species diversity in natural and experimental pond communities of plankton under the metacommunity framework. A further test of the role of dispersal and assembly history is presented in Chapter 2 using experimental pond mesocosms. This study evaluates the role of ecosystem size on the assembly and structure of a multitrophic community of both plankton and macroinvertebrates while concurrently varying nutrient input rate and initial assembly. Chapter 3 empirically illustrates variation in the dormancy-dispersal strategies used by freshwater zooplankton that can lead to interspecific differences in the degree and type of dispersal limitation. In Chapter 4, I use the distribution of single lake endemic fish in the largest lakes in the world to estimate the relative contributions of lake surface area, age, and latitude on diversification.