Microbial species-area relationships in Antarctic cryoconite holes

The island species-area relationship (ISAR) is a positive association between the number of species and the area of an isolated, island-like habitat. ISARs are ubiquitous across domains of life, yet the processes generating ISARs remain poorly understood, particularly for microbes. Larger, and more productive, islands are hypothesized to have more species because they support larger populations of each species and thus reduce the probability of stochastic extinctions due to small population sizes. Here we disentangled size and productivity in Antarctic cryoconite holes: sediment-filled melt holes on glacial surfaces. We compared species richness of bacteria and microbial eukaryotes on two glaciers that differ in their productivity, across varying hole sizes. We found that cryoconite holes on the Canada Glacier contained more species of both bacteria and eukaryotes than holes on the less productive Taylor Glacier. Our results are therefore consistent with productivity shaping microbial ISARs at broad scales. More comparisons of microbial ISARs across environments with limited confounding factors, such as cryoconite holes, and experimental manipulations within these systems will further contribute to our understanding of the processes shaping microbial biogeography.