Effects of dispersal and selection on stochastic assembly in microbial communities

Effects of dispersal and selection on stochastic assembly in microbial communities

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ORIGINAL ARTICLE Effects of dispersal and selection on stochastic assembly in microbial communities Sarah Evans 1,2 , Jennifer BH Martiny 2 and Steven D Allison 2,3 1 W.K. Kellogg Biological Station, Department of Integrative Biology, Michigan State University, Hickory Corners, MI, USA; 2 Department of Ecology and Evolutionary Biology, University of California, Irvine, CA, USA and 3 Department of Earth System Science, University of California, Irvine, CA, USA Stochastic processes can play an important role in microbial community assembly. Dispersal limitation is one process that can increase stochasticity and obscure relationships between environmental variables and microbial community composition, but the relationship between dispersal, selection and stochasticity has not been described in a comprehensive way. We examine how dispersal and its interactions with drift and selection alter the consistency with which microbial communities assemble using a realistic, individual-based model of microbial decomposers. Communities were assembled under different environmental conditions and dispersal rates in repeated simulations, and we examined the compositional difference among replicate communities colonizing the same type of leaf litter ( within-group distance ), as well as between-group deterministic selection. Dispersal rates below 25% turnover per year resulted in high within-group distance among communities and no significant environmental effects. As dispersal limitation was alleviated, both within- and between-group distance decreased, but despite this homogenization, deterministic environmental effects remained significant. In addition to direct effects of dispersal rate, stochasticity of community composition was influenced by an interaction between dispersal and selection strength. Specifically, communities experiencing stronger selection (less favorable litter chemistries) were more stochastic, possibly because lower biomass and richness intensified drift or priority effects. Overall, we show that dispersal rate can significantly alter patterns of community composition. Partitioning the effects of dispersal, selection and drift based on static patterns of microbial composition will be difficult, if not impossible. Experiments will be required to tease apart these complex interactions between assembly processes shaping microbial communities. The ISME Journal advance online publication, 5 August 2016; doi:10.1038/ismej.2016.96 Introduction A common framework to understand community assembly is the distinction between deterministic, or niche-driven, processes and those that are stochastic or neutral (Hubbel, 2001; Vellend et al. , 2014). Because microbes have high dispersal rates, large population sizes, fast growth rates and a propensity for dormancy, communities were traditionally thought to assemble deterministically.
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  • Fall '16
  • Statistics, Stochastic process, Microbial ecology, ISME Journal, The ISME Journal, dispersal rates

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