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Trends and cohort resonant effects in age-structured populations

  1. OTTAR N. BJØRNSTAD1,*,
  2. ROGER M. NISBET2,
  3. JEAN-MARC FROMENTIN3

Article first published online: 29 OCT 2004

DOI: 10.1111/j.0021-8790.2004.00888.x

Issue

Journal of Animal Ecology

Journal of Animal Ecology

Volume 73, Issue 6, pages 1157–1167, November 2004

Additional Information

How to Cite

BJØRNSTAD, O. N., NISBET, R. M. and FROMENTIN, J.-M. (2004), Trends and cohort resonant effects in age-structured populations. Journal of Animal Ecology, 73: 1157–1167. doi: 10.1111/j.0021-8790.2004.00888.x

Author Information

  1. 1

    Departments of Entomology and Biology, The Pennsylvania State University, State College, Pennsylvania 16802, USA;

  2. 2

    Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106, USA

  3. 3

    IFREMER, Centre de Recherche Halieutique Méditerranden et Tropical, Boulevard Jean Monnet, BP 171, 34203 Sète cedex, France

* Ottar N. Bjørnstad, Departments of Entomology and Biology, The Pennsylvania State University, State College, Pennsylvania 16802. USA. Fax: 814 865 3048; E-mail: onbl@psu.edu

Publication History

  1. Issue published online: 29 OCT 2004
  2. Article first published online: 29 OCT 2004
  3. Received 23 November 2003; accepted 22 April 2004

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Keywords:

  • environmental stochasticity;
  • fish populations;
  • stochastic age-structured dynamics;
  • stock-recruitment;
  • transfer functions;
  • trends

Summary

  • 1
    Trends and fluctuations in populations are determined by complex interactions between extrinsic forcing and intrinsic dynamics. As an example, the dynamics of many marine fish are characterized by age-structured dynamics forced by stochastic recruitment.
  • 2
    In this study we develop stochastic age-structured models for two case studies, the Atlantic bluefin tuna and the Atlantic cod. The former exemplifies intracohort interactions and density-dependent reproduction, the latter exemplifies density-dependent survival and intercohort interactions.
  • 3
    We use transfer functions and delay-coordinate models to study how the combination of age-structured interactions and stochastic recruitment can induce low-frequency variability. ‘Cohort resonance’, as we dub this effect, can induce apparent trends in abundance and may be common in age-structured populations.
  • 4
    Our study complements the theory of structured populations that focuses on cycles and chaos (high-frequency dynamics).
  • 5
    The innate low-frequency fluctuations we describe can potentially mimic or cloak critical variation in abundance linked to environmental change, over-exploitation or other types of anthropogenic forcing.
  • 6
    From a management and conservation viewpoint, it will be important to find ways to separate anthropogenic forcing from cohort resonant effects and/or to understand the way they interact.
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