A central question in ecology is how to identify the mechanisms that determine biological diversity. In microbial ecology the total evolutionary history encompassed by a group of organisms, known as phylogenetic diversity, is increasingly the currency with which we quantify this diversity. But we currently lack an understanding both of the basic structure of phylogenetic diversity in microbial communities, and the mechanisms shaping this structure.
I will explore these issues in the context of macroecology: broadly defined in terms of patterns of diversity on large scales. In this talk I will document three macroecological patterns for bacterial communities, and relate these patterns to a family of mathematical models for phylogenetic tree structure, known as lambda coalescents. These patterns strongly suggest that there are bursts of diversification dotted throughout the trees--almost simultaneous coalescence of more than two lineages frequently occurs--and the distribution of the sizes of these bursts is self-similar.