Lifestyles of rarity: Understanding heterotrophic strategies to inform the ecology of the microbial rare biosphere

Abstract

There are patterns in the dynamics of rare taxa that lead to hypotheses about their lifestyles. For example, persistently rare taxa may be oligotrophs that are adapted for efficiency in resource-limiting environments, while conditionally rare or blooming taxa may be copiotrophs that are adapted to rapid growth when resources are available. Of course, the trophic strategies of microorganisms have direct ecological implications for their abundances, contributions to community structure, and role in nutrient turnover. We summarize general frameworks for separately considering rarity and heterotrophy, pulling examples from a variety of ecosystems. We then integrate these 2 topics to discuss the technical and conceptual challenges to understanding their precise linkages. Because much has been investigated especially in marine aquatic environments, we finally extend the discussion to lifestyles of rarity for freshwater lakes by offering case studies of Lake Michigan lineages that have rare and prevalent patterns hypothesized to be characteristic of oligotrophs and copiotrophs. To conclude, we suggest moving forward from assigning dichotomies of rarity/prevalence and oligotrophs/copiotrophs towards their more nuanced continua, which can be linked via genomic information and coupled to quantifications of microbial physiologies during cell maintenance and growth.