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A global test of ecoregions

Abstract

A foundational paradigm in biological and Earth sciences is that our planet is divided into distinct ecoregions and biomes demarking unique assemblages of species. This notion has profoundly influenced scientific research and environmental policy. Given recent advances in technology and data availability, however, we are now poised to ask whether ecoregions meaningfully delimit biological communities. Using over 200 million observations of plants, animals and fungi we show compelling evidence that ecoregions delineate terrestrial biodiversity patterns. We achieve this by testing two competing hypotheses: the sharp-transition hypothesis, positing that ecoregion borders divide differentiated biotic communities; and the gradual-transition hypothesis, proposing instead that species turnover is continuous and largely independent of ecoregion borders. We find strong support for the sharp-transition hypothesis across all taxa, although adherence to ecoregion boundaries varies across taxa. Although plant and vertebrate species are tightly linked to sharp ecoregion boundaries, arthropods and fungi show weaker affiliations to this set of ecoregion borders. Our results highlight the essential value of ecological data for setting conservation priorities and reinforce the importance of protecting habitats across as many ecoregions as possible. Specifically, we conclude that ecoregion-based conservation planning can guide investments that simultaneously protect species-, community- and ecosystem-level biodiversity, key for securing Earth’s life support systems into the future.

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All data used in this study are publicly available from either www.gbif.org or www.fia.fs.fed.us

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Change history

  • 11 March 2019

    The original paper was published without unique DOIs for GBIF occurrence downloads. These have now been inserted as references 70–76, and the error has been corrected in the PDF and HTML versions of the article.

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Acknowledgements

This work was supported financially by the National Science Foundation’s Graduate Research Fellowship Program Division of Graduate Education No. 1656518, the Stanford Department of Biology and the Ward Wilson Woods Jr Environmental Studies Fund (to J.R.S.). Some of the computing for this project was performed on the Sherlock cluster. We would like to thank Stanford University and the Stanford Research Computing Center for providing computational resources and support that contributed to these research results. We thank K. Peay, T. Fukami, B. Brosi and B. Bryant for discussions that increased the quality of the manuscript.

Author information

J.R.S., A.D.L. and P.J.K developed the original concept. J.R.S., A.D.L., P.J.K., C.B.A., J.N.H., M.K.D., G.A.D., T.N.G., M.E.H., B.M.L.M. and P.A.S.J. developed the model. J.R.S., C.B.A., D.R. and T.W.C. carried out the spatial analysis. J.R.S. and T.W.C. gathered and analysed supplementary data from the USFS FIA. J.R.S. wrote and edited the manuscript with input from all authors.

Competing interests

The authors declare no competing interests.

Correspondence to Jeffrey R. Smith.

Supplementary information

  1. Supplementary Information

    Supplementary Methods, Supplementary Tables 1–3 and Supplementary Figures 1–14

  2. Reporting Summary

  3. Supplementary Tables 2 and 3

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Fig. 1: Our approach to testing the sharp-transition and gradual-transition hypotheses.
Fig. 2: Species-accumulation curves from transects representing our two hypotheses.
Fig. 3: Summary of results from species-accumulation curve tests.
Fig. 4: Distance-similarity matrices from transects representing our two hypotheses.
Fig. 5: Summary of results from distance-similarity matrices tests.
Fig. 6: Relationship between geographical distance and community similarity in USFS FIA tree plots.