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Expanding the mutualistic niche: parallel symbiont turnover along climatic gradients


Rolshausen, Gregor et al. (2020), Expanding the mutualistic niche: parallel symbiont turnover along climatic gradients, Dryad, Dataset,


Keystone mutualisms, such as corals, lichens, or mycorrhizae sustain fundamental ecosystem functions. Range dynamics of these symbioses are, however, inherently difficult to predict because host species may switch between different symbiont partners in different environments, thereby altering the range of the mutualism as a functional unit. Biogeographic models of mutualisms thus have to consider both, the ecological amplitudes of various symbiont partners, and the abiotic conditions that trigger symbiont replacement. To address this challenge, we here investigate ‘symbiont turnover zones’ – defined as demarcated regions where symbiont replacement most likely occurs due to overlapping abundances of symbiont ecotypes. Mapping the distribution of algal symbionts from two species of lichen-forming fungi along four independent altitudinal gradients, we detected an abrupt and consistent β-diversity turnover suggesting parallel niche partitioning. Modeling contrasting environmental response functions obtained from latitudinal distributions of algal ecotypes consistently predicted a confined altitudinal turnover zone. In all gradients this symbiont turnover zone is characterized by ~12°C average annual temperature, ~5°C mean temperature of the coldest quarter, marking the transition from Mediterranean to cool temperate bioregions. Integrating conditions of symbiont turnover into biogeographic models of mutualisms is an important step towards a comprehensive understanding of biodiversity dynamics under ongoing environmental change.


Ministry of Education, Youth and Sports of the Czech Republic, Award: LTAUSA18188