Interplay between spatial structure and competition in ecological communities

Abstract

Ecology, much like physics, has a long history of theoretical contribution. In this thesis, we take a physics approach to describing ecological communities, searching for simple, emergent features that can generalize beyond specific models of community dynamics. Unifying all of the models we study is an underlying spatial structure, leading to a richer set of possible behaviors than a typical well-mixed model. We first study the case of a metapopulation, a collection of smaller communities linked by dispersal. We find that when the environment is allowed to fluctuate stochastically, new growth laws emerge at the single species level, and high diversity is achieved in the case with many species. We then study the case of pathogen evolution, again in the metapopulation framework. We find that intermediate dispersal can act as a strong driver of pathogen evolution. We also study what happens as a population of microbes expands into unexplored territory, known as a range expansion. We find that a simple model can capture all morphological phases observed in experiments and predict invasion fitness as a function of local and global competitive ability. We also break a standard assumption in microbial ecology, the isotropy of space, and find that a new sector morphology emerges.