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Chapter 3 : Lady Lumps's Mouthguard
Charles Darwin’s research on the spatial distribution of macroorganisms formed an integral part of his arguments for natural selection and played a foundational role in the burgeoning field of biogeography. Darwin recognized three biogeographic patterns that he described in terms of “great facts” in On the Origin of Species. In summary, these are: (i) environmental conditions alone cannot account for the dissimilarity of flora and fauna among geographically distinct regions; (ii) barriers to dispersal significantly contribute to these differences; and (iii) although the spatial variability in community composition within regions is substantial, these communities remain evolutionarily related. The prevailing view of Darwin and his contemporaries was that microorganisms (microbes) are dispersed globally and able to proliferate in any habitat with suitable environmental conditions. Microbial diversity shifts across the surface of the Earth as a consequence of the three forces highlighted by Darwin when considering plants and animals: the environment, dispersal, and diversification. The author’s laboratory is striving to overcome limitations of time, resources, and sequencing efficiency, by developing a spatial theory of community assembly that quantifies the evolutionary relatedness among individuals (or genomes or genes) within and among sample locations across the landscape. This new framework combines four crucial ingredients: spatial dispersal, by which individuals disperse seeds or move across a spatial landscape; evolutionary diversification, through which genetic novelty is introduced to a community; individual-based processes, so that the discrete nature of individuals is accounted for; and demographic stochasticity, the random nature of birth, death, and dispersal processes.