I discuss the importance of oxygen-scarce (hypoxic) wetlands in the maintenance of fish faunal structure and diversity in East Africa:
First, I explore the role of dissolved oxygen as a divergent selective factor contributing to interdemic variation in freshwater fishes. Given the widespread nature of hypoxia in aquatic systems, and increasing levels of hypoxia associated with anthropogenic perturbations, microevolution in response to hypoxic stress may be a frequent phenomenon in nature. Over the past few years, our studies of East African fishes have demonstrated interdemic variation in respiratory traits in a suite of fishes that occur across gradients of dissolved oxygen availability. For two focal species, we have also established that variation in gill size is adaptive but can negatively impact non-respiratory characters, creating a fitness trade-off between high- and low-oxygen environments that may contribute to the maintenance of local phenotypes.
Second, I apply our understanding of respiratory ecology to current conservation issues in the region—in particular, the importance of hypoxic wetlands as refugia and their potential effects on patterns of biodiversity loss and recovery in the Lake Victoria Region. The explosive speciation of haplochromine cichlid fishes in Lake Victoria is unrivaled among vertebrates; however, over 40% of the lake's endemic fishes disappeared between 1980 and 1986, which is associated with various anthropogenic perturbations, including the introduction of the predatory Nile perch. Our research has demonstrated the importance of physiological refugia in modulating the impact of introduced predators on indigenous fish communities, and highlighted the importance of wetland conservation.
My research combines ecological and physiological approaches to understand the evolution of freshwater fishes and applies these approaches to current conservation issues in tropical fresh waters. Currently, my major thematic focus is the study of evolutionary and ecological consequences of respiratory strategies in fishes. I am particularly interested in the role of hypoxia (oxygen scarcity) as a factor influencing the dispersal, distribution, and abundance of fishes, and adaptations of fishes to extreme environments. I have used studies of ecophysiology, ecomorphology, population ecology, and community ecology to investigate this theme. My current work in this area emphasizes links between the physico-chemical environment and patterns of interdemic variation. I have carried out fieldwork in many areas of the world (Canada, Barbados, Costa Rica, East Africa) with a current focus on lakes, rivers, and in particular, wetlands of Uganda.