Quasi-cycles in crappie populations are forced by interactions among population characteristics and environment

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Crappie (Pomoxis spp.) populations have been characterized as cyclic, with strong year-classes recurring at 2- to 4-year intervals. We evaluated the potential for cyclic trends in crappie populations using a population model that included a density-dependent stock recruitment function and random environmental variation. Slow, medium, and fast growth were simulated over 100 years. The model predicted highly variable recruitment that was strongly influenced by environmental fluctuation at low and intermediate stock densities. At high stock density, recruitment was low, even if environmental conditions were favorable. Significant quasi-cycles occurred, but they were not sustained throughout the time series due to random environmental fluctuation. Quasi-cycles occurred because intermediate stock density and favorable environmental conditions occasionally combined to produce a very strong year-class that greatly increased stock density in the following 1–3 years and produced low recruitment, even if environmental conditions were favorable. Empirical data from 32 years of sampling age-0 crappies at Ross Barnett Reservoir showed trends similar to the simulated fluctuations. We conclude that crappie populations likely do not exhibit true cycles but may show quasi-cycles as a result of the interaction between random fluctuations in environment and density-dependent mechanisms. The frequency of such quasi-cycles may be enhanced by rapid growth and high exploitation.

Les populations de mariganes, Pomoxis spp., ont été définies comme cycliques, avec des classes d'âge plus importantes réapparaissant à des intervalles de 2-4 ans. Un modèle de population qui inclut une fonction de recrutement du stock dépendante de la densité et une variation aléatoire de l'environnement a permis d'évaluer l'existence de tendances cycliques chez les mariganes. Des croissances lentes, moyennes et rapides ont été simulées sur des périodes de 100 ans. Le modèle prédit, aux densités basses et intermédiaires de stock, un recrutement très variable qui est influencé par les fluctuations environnementales. Aux fortes densités, le recrutement est faible, même lorsque les conditions environnementales sont favorables. Il y a des quasi-cycles significatifs, mais ils ne se maintiennent pas au cours de séries temporelles à cause de la fluctuation aléatoire de l'environnement. Ces quasi-cycles apparaissent parce que la combinaison occasionnelle d'une densité moyenne du stock et des conditions favorables du milieu génère une classe d'âge beaucoup plus importante qui augmente la densité du stock pendant les 1–3 années subséquentes et donne lieu à un faible recrutement, même en présence conditions environnementales favorables. Des données empiriques provenant de 32 années d'échantillonnage de mariganes d'âge 0 au réservoir Ross Barnett montrent des tendances semblables aux fluctuations simulées par le modèle. En conclusion, les populations de mariganes ne subissent vraisemblablement pas de vrais cycles, mais elles affichent des quasi-cycles qui résultent de l'interaction entre les fluctuations aléatoires de l'environnement et les mécanismes dépendants de la densité. La fréquence de tels quasi-cycles peut être accrue par une croissance rapide et une forte exploitation.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2001

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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