Low Stream Flow Promotes Endemism And Lowers Diversity In Dry Valley Diatoms
Esposito, Rhea M M 1 ; Horn, Shannon 2 ; McKnight, Diane 3
1 INSTAAR
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3
The McMurdo Dry Valleys in Antarctica are among the coldest and driest deserts on earth. Streams only flow for 6-10 weeks per year, but streams support perennial microbial mats dominated by phototrophic cyanobacteria, chlorophyta, and bacillariophyta. These valleys are characterized by a low diversity of organisms. As part of studying the glacial melt water streams in the McMurdo Long Term Ecological Research project, we found 40 diatom species in high abundance, 24 of which are Antarctic endemics. Eighteen of these endemic species are found only in South Victoria Land. Twelve species are new to science. We illustrate a negative linear relationship between endemism and annual stream flow, which is related to other environmental conditions affected by climate change. We found that diversity and endemism have a curvilinear quadratic relationship (highest diversity at intermediate levels of endemism) for freshwater diatoms in glacial meltwater streams of the Dry Valleys. During low flow events, as endemism increases, diversity drops. Counter to expectations for extreme environments, our data show that co-occurrence of endemic species with widespread species promotes diversity in diatom assemblages, and low flow raises endemism and lowers diversity.