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Size differences predict niche and relative fitness differences between phytoplankton species but not their coexistence

The ISME Journal (2019) | Download Citation


Here we aim to incorporate trait-based information into the modern coexistence framework that comprises a balance between stabilizing (niche-based) and equalizing (fitness) mechanisms among interacting species. Taking the modern coexistence framework as our basis, we experimentally tested the effect of size differences among species on coexistence by using fifteen unique pairs of resident vs. invading cyanobacteria, resulting in thirty unique invasibility tests. The cyanobacteria covered two orders of magnitude differences in size. We found that both niche and fitness differences increased with size differences. Niche differences increased faster with size differences than relative fitness differences and whereas coexisting pairs showed larger size differences than non-coexisting pairs, ultimately species coexistence could not be predicted on basis of size differences only. Our findings suggest that size is more than a key trait controlling physiological and population-level aspects of phytoplankton, it is also relevant for community-level phenomena such as niche and fitness differences which influence coexistence and biodiversity.

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IG was supported by a grant from the Swiss State Secretariat for Education, Research and Innovation (SERI) to BWI, linked to the EU NETLAKE COST Action. We would like to thank Anita Narwani, Ian T. Carroll and Oscar Godoy for valuable comments on earlier versions of the manuscript.

Author contributions

All authors conceived the study. IG performed the experiment, collected data, analyzed data and wrote the first draft of the manuscript. PV contributed to data analysis, figure conception and to revisions. All authors commented on the manuscript.

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  1. Department F.-A. Forel for Environmental and Aquatic Sciences (DEFSE), Institute for Environmental Sciences (ISE), University of Geneva, Geneva, Switzerland

    • Irene Gallego
    • , Patrick Venail
    •  & Bas W. Ibelings


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The authors declare that they have no conflict of interest.

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Correspondence to Irene Gallego.

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