The Rich Get Richer: Cryoconite Holes on Antarctic Glaciers with More Microbes Accumulate Diversity More Rapidly with Size, Independent of Local Biogeochemistry

Abstract:

The diversity-area relationship (DAR) in island-like habitats is a saturating positive association between size of a habitat patch and the diversity of the organisms found there. DARs are ubiquitous across domains and scales, from plants and animals to bacteria, fungi, and ciliates. Yet the mechanistic drivers of DARs – and deviations from the relationships –remain elusive, particularly in microbial biogeography where a challenge in the field is to move from describing patterns to developing a predictive understanding of their underlying processes. Larger habitats are hypothesized to have greater richness because they are more populous, and we tested this hypothesis using Antarctic cryoconite holes as a model system. We used illumina sequencing to characterize the diversity of bacteria and microbial eukaryotes found in these sediment-filled melt-holes (island-like habitats) in the surfaces of Antarctic glaciers. We compared the DAR on two glaciers that differ in their concentrations of nitrogen, phosphorus, carbon, as well as concentrations of chlorophyll a and organic matter. Larger holes contained significantly more species than smaller holes on both glaciers, as expected, and importantly, small holes accumulated diversity more rapidly with area on the high-biomass glacier. Deviations from DARs within each glacier were not significantly related to biomass or other biogeochemical measurements, however, suggesting that unknown stochastic processes (likely drift) play a significant role in the maintenance of cryoconite hole biodiversity, and that biogeochemistry structures DARs at broad, but not localized, scales.