Testate Amoebae Like It Hot: Species Richness Decreases Along a Subalpine-Alpine Altitudinal Gradient in Both Natural Calluna vulgaris Litter and Transplanted Minuartia sedoides Cushions T. J. Heger 1 & N. Derungs 2 & J .P. Theurillat 3,4 & E. A. D. Mitchell 2,5 Abstract Most groups of higher organisms show a decrease in species richness toward high altitude, but the existence of such a pattern is debated for micro-eukaryotes. Existing data are scarce and mostly confounded with the diversity of habi- tats that also decreases with elevation. In order to disentangle these two factors, one approach is to consider only similar types of habitats occurring across an elevational gradient. We assessed the diversity and community structure of testate amoebae in two specific habitats: (1) natural Calluna vulgaris litter and (2) Minuartia sedoides cushions 7 years after their transplantation along a vertical transect from 1770 to 2430 m in the subalpine and alpine zones of the Swiss Alps. Analyses of co-variance and variance showed that testate amoeba spe- cies richness, equitability, and diversity declined with eleva- tion and were significantly correlated to habitat type. In a redundancy analysis, the variation in the relative abundance of the testate amoeba taxa in Calluna vulgaris litter was equal- ly explained by elevation and litter pH. This is the first study documenting a monotonic decrease of protist diversity in sim- ilar habitats across an elevational gradient. Keywords Biodiversity patterns . Elevational gradient . Micro-eukaryotes . Pot experiment . Protists . Soil Introduction Examining the distribution of organisms along elevational gra- dients is a classical approach used for understanding the broad- scale distribution of species, the mechanisms that shape their biogeographical patterns and the influence of global change on protist communities. In most groups of macroorganisms, spe- cies diversity peaks at low latitudes and decreases toward higher latitudes (e.g., [1]), whereas along elevational gradients, a monotonic decrease in biodiversity toward higher altitude or a mid-elevational peak along the elevational gradient is generally observed [2–4]. Although microorganisms dominate biodiver- sity on earth and play essential roles in biogeochemical cycles and food web processes [5, 6], it still remains unclear whether patterns of diversity are similar for soil microorganisms and in particular for micro-eukaryotes. With respect to micro-eukaryotes, diversity patterns along elevational gradients were mostly studied for diatoms (Stramenopiles) and testate amoebae (Amoebozoa, Rhizaria, and Stramenopiles [7]). Gremmen et al. [8] reported a negative relationship between moss-inhabiting diatom species diversity along a 550-m altitudinal gradient on the sub-Antarctic Electronic supplementary material The online version of this article (doi:10.1007/s00248-015-0687-3) contains supplementary material, which is available to authorized users. * T. J. Heger thierry.heger@botany.ubc.ca N. Derungs nicolas.derungs@unine.ch J .P. Theurillat jean-paul.theurillat@unige.ch E. A. D. Mitchell edward.mitchell@unine.ch 1 Beaty Biodiversity Center, University of British Columbia, 6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada 2 University of Neuchâtel, Rue Emile-Argand 11, 2000 Neuchâtel, Switzerland 3 Centre Alpien de Phytogéographie, Fondation J.-M. Aubert, 1938 Champex, Switzerland 4 Laboratoire de Biogéographie, Section de Biologie, Université de Genève, Case postale 60, 1292 Chambésy, Switzerland 5 Jardin Botanique de Neuchâtel, Chemin du Perthuis-du-Sault 58, 2000 Neuchâtel, Switzerland Published in Microbial Ecology 71, issue 3, 725-734, 2016 which should be used for any reference to this work 1