| Clustering of types is a dominant feature in evolutionary biology and ecology. Genotypes are clustered into species, and species are spatially clustered in an ecosystem. Aggregation often results from evolutionary or ecological processes. But aggregation also affects the trajectory of future evolutionary and ecological change. In this dissertation, I study the causes and consequences of such aggregation—specifically, the spatial aggregation of individuals in plant communities, and the aggregation of genotypes in rapidly replicating populations.; These topics are unified by a common theme and by common mathematical methodologies. In the ecological setting, I develop methods to address the following types of questions: How can we identify natural scales of spatial aggregation in a census of a plant community? How does conspecific clustering affect overall diversity in plant communities? Is aggregation in tropical rainforests caused by exogenous factors, such as habitat variation, or by intrinsic forces, such a localized seed dispersal? Why are some species more aggregated than others? Given uneven spatial distributions, how can we accurately assess the species composition of a landscape?; In the evolutionary setting, I develop similar methods to address the following questions: How can we identify natural scales of aggregation in a large data set of nucleotide sequences? How do mutation rate, genome length, and population size affect the clustering of individuals around an optimal wildtype sequence? How do cellular lineages maintain a narrow range of genotypic variation throughout an organism's lifetime? How do viruses maintain a tight cluster of genotypes in the presence of mutation? Do evolving viruses change continuously or sporadically? How might evolving viruses adjust their mutation rate in order to facilitate adaptation?; Throughout the dissertation, I use mathematical models and computational tools for the exploration of evolutionary and ecological hypotheses. I make extensive use of tropical forest censuses and viral nucleotide sequence data. |
