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Weakened portfolio effects constrain management effectiveness for population aggregates
Population diversity can reduce temporal variability in aggregate population abundances in a process known as the portfolio effect. Portfolio effects may weaken, however, due to greater synchrony among component populations. While weakened portfolio effects have been previously documented, the conse...
Autores principales: | , , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
John Wiley and Sons Inc.
2019
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6900020/ https://www.ncbi.nlm.nih.gov/pubmed/31257710 http://dx.doi.org/10.1002/eap.1966 |
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author | Freshwater, Cameron Anderson, Sean C. Holt, Kendra R. Huang, Ann‐Marie Holt, Carrie A. |
author_facet | Freshwater, Cameron Anderson, Sean C. Holt, Kendra R. Huang, Ann‐Marie Holt, Carrie A. |
author_sort | Freshwater, Cameron |
collection | PubMed |
description | Population diversity can reduce temporal variability in aggregate population abundances in a process known as the portfolio effect. Portfolio effects may weaken, however, due to greater synchrony among component populations. While weakened portfolio effects have been previously documented, the consequences of reduced stability on meeting conservation goals for population aggregates that are harvested (e.g., stock aggregates in fisheries) are rarely quantified. Here, we demonstrate how changes in variability within components, synchrony among components, and population productivity interact to influence the probability of achieving an array of management objectives for Fraser River sockeye salmon: a stock aggregate of high economic, ecological, and cultural value. We first present evidence that component variability and synchrony have increased over the last two decades, consistent with a weakening portfolio effect. We then parameterize a stochastic, closed‐loop model that simulates the population dynamics of each stock, the fishery that harvests the stock aggregate, and the management framework used to establish mixed‐stock exploitation rates. We find that while median aggregate abundance and catch through time were relatively insensitive to greater aggregate variability, catch stability and performance metrics associated with achieving management targets generally declined as component variability and synchrony increased. A notable exception we observed is that harvest control means that scale exploitation rates based on aggregate abundance may be more effective as synchrony increases. Reductions in productivity led to broad declines in performance, but also moderated the impacts of component variability and synchrony on the proportion of component stocks above management targets and catch stability. Our results suggest that even precautionary management strategies that account for declines in productivity may underestimate risk, particularly to socioeconomic objectives, if they fail to consider changes in aggregate variability. Adequately incorporating changes in portfolio effect strength may be particularly relevant when developing recovery strategies that are robust to climate change, which is likely to increase synchrony and component variability. |
format | Online Article Text |
id | pubmed-6900020 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2019 |
publisher | John Wiley and Sons Inc. |
record_format | MEDLINE/PubMed |
spelling | pubmed-69000202019-12-20 Weakened portfolio effects constrain management effectiveness for population aggregates Freshwater, Cameron Anderson, Sean C. Holt, Kendra R. Huang, Ann‐Marie Holt, Carrie A. Ecol Appl Articles Population diversity can reduce temporal variability in aggregate population abundances in a process known as the portfolio effect. Portfolio effects may weaken, however, due to greater synchrony among component populations. While weakened portfolio effects have been previously documented, the consequences of reduced stability on meeting conservation goals for population aggregates that are harvested (e.g., stock aggregates in fisheries) are rarely quantified. Here, we demonstrate how changes in variability within components, synchrony among components, and population productivity interact to influence the probability of achieving an array of management objectives for Fraser River sockeye salmon: a stock aggregate of high economic, ecological, and cultural value. We first present evidence that component variability and synchrony have increased over the last two decades, consistent with a weakening portfolio effect. We then parameterize a stochastic, closed‐loop model that simulates the population dynamics of each stock, the fishery that harvests the stock aggregate, and the management framework used to establish mixed‐stock exploitation rates. We find that while median aggregate abundance and catch through time were relatively insensitive to greater aggregate variability, catch stability and performance metrics associated with achieving management targets generally declined as component variability and synchrony increased. A notable exception we observed is that harvest control means that scale exploitation rates based on aggregate abundance may be more effective as synchrony increases. Reductions in productivity led to broad declines in performance, but also moderated the impacts of component variability and synchrony on the proportion of component stocks above management targets and catch stability. Our results suggest that even precautionary management strategies that account for declines in productivity may underestimate risk, particularly to socioeconomic objectives, if they fail to consider changes in aggregate variability. Adequately incorporating changes in portfolio effect strength may be particularly relevant when developing recovery strategies that are robust to climate change, which is likely to increase synchrony and component variability. John Wiley and Sons Inc. 2019-07-30 2019-10 /pmc/articles/PMC6900020/ /pubmed/31257710 http://dx.doi.org/10.1002/eap.1966 Text en © 2019 The Authors. Ecological Applications published by Wiley Periodicals, Inc. on behalf of Ecological Society of America This is an open access article under the terms of the http://creativecommons.org/licenses/by-nc/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. |
spellingShingle | Articles Freshwater, Cameron Anderson, Sean C. Holt, Kendra R. Huang, Ann‐Marie Holt, Carrie A. Weakened portfolio effects constrain management effectiveness for population aggregates |
title | Weakened portfolio effects constrain management effectiveness for population aggregates |
title_full | Weakened portfolio effects constrain management effectiveness for population aggregates |
title_fullStr | Weakened portfolio effects constrain management effectiveness for population aggregates |
title_full_unstemmed | Weakened portfolio effects constrain management effectiveness for population aggregates |
title_short | Weakened portfolio effects constrain management effectiveness for population aggregates |
title_sort | weakened portfolio effects constrain management effectiveness for population aggregates |
topic | Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6900020/ https://www.ncbi.nlm.nih.gov/pubmed/31257710 http://dx.doi.org/10.1002/eap.1966 |
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