Diatom Species Richness in Swiss Springs Increases with Habitat Complexity and Elevation

Lukas Taxböck,Michael Kessler,Dirk Nikolaus Karger,Daniel Spitale,Marco Cantonati

doi:10.3390/w12020449

Abstract

Understanding the drivers of species richness gradients is a central challenge of ecological and biodiversity research in freshwater science. Species richness along elevational gradients reveals a great variety of patterns. Here, we investigate elevational changes in species richness and turnover between microhabitats in near-natural spring habitats across Switzerland. Species richness was determined for 175 subsamples from 71 near-natural springs, and Poisson regression was applied between species richness and environmental predictors. Compositional turnover was calculated between the different microhabitats within single springs using the Jaccard index based on observed species and the Chao index based on estimated species numbers. In total, 539 diatom species were identified. Species richness increased monotonically with elevation. Habitat diversity and elevation explaining some of the species richness per site. The Jaccard index for the measured compositional turnover showed a mean similarity of 70% between microhabitats within springs, whereas the Chao index which accounts for sampling artefacts estimated a turnover of only 37%. Thus, the commonly applied method of counting 500 valves led to an undersampling of the rare species and might need to be reconsidered when assessing diatom biodiversity.

Highlights

Understanding the factors that drive gradients of species richness is one of the major challenges of ecological and biogeographical research
Compositional turnover was calculated between the different microhabitats within single springs using the Jaccard index based on observed species and the Chao index based on estimated species numbers
The Jaccard index for the measured compositional turnover showed a mean similarity of 70% between microhabitats within springs, whereas the Chao index which accounts for sampling artefacts estimated a turnover of only 37%

Summary

Introduction

Understanding the factors that drive gradients of species richness is one of the major challenges of ecological and biogeographical research. To investigate patterns of species richness and the related environmental drivers, elevational gradients have received considerable attention in the last decade, and have become firmly established as a replicable methodology [1,2,3,4]. Patterns of species richness along elevational gradients can, contrast with those of macroorganisms [6] and the determinants of elevational distributions of microorganism species richness are still poorly understood. Studying microorganisms along elevational gradients might provide important insights into the processes determining species richness along elevational gradients. Different aspects of biodiversity can be driven by different main factors: Wang et al [7] for instance, found for stream diatom assemblages along elevational gradients

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