Abstract

The tropical forests of Borneo and Amazonia may each contain more tree species diversity in half a square kilometre than do all the temperate forests of Europe, North America, and Asia combined1. Biologists have long been fascinated by this disparity, using it to investigate potential drivers of biodiversity2. Latitudinal variation in many of these drivers is expected to create geographic differences in ecological2,3,4 and evolutionary processes4,5, and evidence increasingly shows that tropical ecosystems have higher rates of diversification, clade origination, and clade dispersal5,6. However, there is currently no evidence to link gradients in ecological processes within communities at a local scale directly to the geographic gradient in biodiversity. Here, we show geographic variation in the storage effect, an ecological mechanism that reduces the potential for competitive exclusion more strongly in the tropics than it does in temperate and boreal zones, decreasing the ratio of interspecific-to-intraspecific competition by 0.25% for each degree of latitude that an ecosystem is located closer to the Equator. Additionally, we find evidence that latitudinal variation in climate underpins these differences; longer growing seasons in the tropics reduce constraints on the seasonal timing of reproduction, permitting lower recruitment synchrony between species and thereby enhancing niche partitioning through the storage effect. Our results demonstrate that the strength of the storage effect, and therefore its impact on diversity within communities, varies latitudinally in association with climate. This finding highlights the importance of biotic interactions in shaping geographic diversity patterns, and emphasizes the need to understand the mechanisms underpinning ecological processes in greater detail than has previously been appreciated.

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Acknowledgements

We thank J. M. Levine, M. G. Turner, D. M. Waller, D. J. Mladenoff and J. Zhu for comments on the manuscript, and S.-H. Wu of the Taiwan Forestry Research Institute for plant identification. We acknowledge the following funding sources, which have been essential in the ongoing collection of long-term forest data (in alphabetical order): Andrew M. Mellon Foundation, Center for Tropical Forest Science, Environment Research and Technology Development Fund of the Japan Ministry of the Environment, JSPS KAKENHI, National Key Research and Development Program of China, National Natural Science Foundation of China, National Science Foundation of the United States (DDIG, IGERT, LTER, LTREB), Natural Environment Research Council of the UK, Natural History Museum of London, Smithsonian Tropical Research Institute, Taiwan Forestry Bureau, Taiwan Forestry Research Institute, Taiwan Ministry of Science and Technology, USDA Forest Service.

Author information

Affiliations

  1. Department of Integrative Biology, University of Wisconsin, Madison, Wisconsin, USA

    • Jacob Usinowicz
    •  & Anthony R. Ives
  2. Department of Natural Resources and Environmental Studies, National Dong Hwa University, Hualien, Taiwan

    • Chia-Hao Chang-Yang
    • , Yu-Yun Chen
    •  & I-Fang Sun
  3. Nicholas School of the Environment, Duke University, Durham, North Carolina, USA

    • James S. Clark
  4. Forest Research Institute Malaysia, Kuala Lumpur, Malaysia

    • Christine Fletcher
  5. Department of Plant Biology, Southern Illinois University, Carbondale, Illinois, USA

    • Nancy C. Garwood
  6. Institute of CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China

    • Zhanqing Hao
    •  & Yunyun Wang
  7. Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, Alaska, USA

    • Jill Johnstone
  8. Department of Life Science, Tunghai University, Taichung, Taiwan

    • Yiching Lin
  9. Biology Department, Lewis & Clark College, Portland, Oregon, USA

    • Margaret R. Metz
  10. Forestry and Forest Products Research Institute, Tsukuba, Ibaraki, Japan

    • Takashi Masaki
  11. Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi, Japan

    • Tohru Nakashizuka
  12. Research Institute for Humanity and Nature, Kyoto, Japan

    • Tohru Nakashizuka
  13. Laboratorio de Ecología de Plantas, Herbario QCA, Pontificia Universidad Católica del Ecuador, Quito, Ecuador

    • Renato Valencia
  14. Department of Environmental Science, University of Puerto Rico at Rio Piedras, San Juan, Puerto Rico

    • Jess K. Zimmerman
    •  & S. Joseph Wright
  15. Smithsonian Tropical Research Institute, Apartado 0843–03092, Balboa, Panama

    • S. Joseph Wright

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Contributions

J.U. analysed data and wrote the paper. C.-H.C.–Y., Y.-Y.C., J.S.C., C.F., N.C.G., Z.H., J.J., Y.L., M.R.M., T.M., T.N., I.S., R.V., Y.W., J.K.Z., and S.J.W. have established, maintained, and collected data from long-term demography plots. S.J.W. and A.R.I. contributed equally to paper conception and development. All authors discussed results and commented on the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Jacob Usinowicz.

Reviewer Information Nature thanks R. Bagchi, S. McMahon, G. Mittelbach and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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DOI

https://doi.org/10.1038/nature24038

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