Metapopulation stability in branching river networks

Akira Terui, Nobuo Ishiyama, Hirokazu Urabe, Satoru Ono, Jacques C. Finlay, Futoshi Nakamura

Research output: Contribution to journalArticlepeer-review

19 Scopus citations

Abstract

Intraspecific population diversity (specifically, spatial asynchrony of population dynamics) is an essential component of metapopulation stability and persistence in nature. In 2D systems, theory predicts that metapopulation stability should increase with ecosystem size (or habitat network size): Larger ecosystems will harbor more diverse subpopulations with more stable aggregate dynamics. However, current theories developed in simplified landscapes may be inadequate to predict emergent properties of branching ecosystems, an overlooked but widespread habitat geometry. Here, we combine theory and analyses of a unique long-term dataset to show that a scale-invariant characteristic of fractal river networks, branching complexity (measured as branching probability), stabilizes watershed metapopulations. In riverine systems, each branch (i.e., tributary) exhibits distinctive ecological dynamics, and confluences serve as “merging” points of those branches. Hence, increased levels of branching complexity should confer a greater likelihood of integrating asynchronous dynamics over the landscape. We theoretically revealed that the stabilizing effect of branching complexity is a consequence of purely probabilistic processes in natural conditions, where within-branch synchrony exceeds among-branch synchrony. Contrary to current theories developed in 2D systems, metapopulation size (a variable closely related to ecosystem size) had vague effects on metapopulation stability. These theoretical predictions were supported by 18-y observations of fish populations across 31 watersheds: Our cross-watershed comparisons revealed consistent stabilizing effects of branching complexity on metapopulations of very different riverine fishes. A strong association between branching complexity and metapopulation stability is likely to be a pervasive feature of branching networks that strongly affects species persistence during rapid environmental changes.

Original languageEnglish (US)
Pages (from-to)E5963-E5969
JournalProceedings of the National Academy of Sciences of the United States of America
Volume115
Issue number26
DOIs
StatePublished - Jun 26 2018

Bibliographical note

Funding Information:
ACKNOWLEDGMENTS. We thank the numerous people who worked hard to collect and organize the large datasets of protected watersheds. We are grateful to three anonymous reviewers and to Shota Nishijima, Keisuke Atsumi, and Shin-ichiro S. Matsuzaki for their constructive comments on the manuscript. We thank Jesús N. Pinto-Ledezma, Josep Padullés Cubino, and the theory group at the University of Minnesota for helpful discussion. This research was partly supported by Japan Society for the Promotion of Science KAKENHI Grant 18K06404 (to A.T.).

Funding Information:
We thank the numerous people who worked hard to collect and organize the large datasets of protected watersheds. We are grateful to three anonymous reviewers and to Shota Nishijima, Keisuke Atsumi, and Shin-ichiro S. Matsuzaki for their constructive comments on the manuscript. We thank Jesús N. Pinto-Ledezma, Josep Padullés Cubino, and the theory group at the University of Minnesota for helpful discussion. This research was partly supported by Japan Society for the Promotion of Science KAKENHI Grant 18K06404 (to A.T.).

Publisher Copyright:
© 2018 National Academy of Sciences. All Rights Reserved.

Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

Keywords

  • Dendritic ecological network
  • Dispersal
  • Portfolio effect
  • Spatially structured population
  • Stream

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