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Resource matching across habitats is limited by competition at patch scales in an estuarine-opportunist fish

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Abstract:

I used field observations, assays, and experiments with the euryhaline cottid Cottus aleuticus to evaluate the extent to which average resource availability drives the large-scale distribution of these fish among upstream and estuarine habitats and how interspecific competition from a congener affects its performance in the estuary. Population densities of C. aleuticus were only consistent with resource densities across years during two of five study years, indicating a lack of resource matching at large temporal scales. On shorter temporal scales, fish growth rates that were two to three times higher in the estuary compared with the stream were inconsistent with the predictions of resource matching theory. A manipulation of C. aleuticus density showed that the estuary could support at least twice the number of individuals that occurred there; thus, the profitable estuary is underutilized. Interspecific competition with Cottus asper was partially responsible for this underutilization as indicated by a substantial reduction in growth and condition among C. aleuticus individuals in experimental manipulations that compared intra- and inter-specific effects. Observed spatial overlap between these two cottids combined with the results of the competition experiment suggests that C. aleuticus is more strongly limited in its ability to use estuarine habitats opportunistically by interspecific competition than by intraspecific competition.

Des observations de terrain, des tests et des expériences avec le cottidé euryhalin Cottus aleuticus ont permis d'évaluer en quelle mesure la disponibilité moyenne des ressources explique la répartition à grande échelle de ce poisson dans les habitats fluviaux d'amont et dans l'estuaire et comment la compétition interspécifique par un congénère affecte sa performance dans l'estuaire. Les densités de population de C. aleuticus ne correspondent aux densités des ressources que durant deux des cinq années de l'étude, ce qui indique une absence d'appariement des ressources aux grandes échelles temporelles. Aux échelles temporelles plus courtes, les taux de croissance des poissons, qui sont deux–trois fois plus élevés dans l'estuaire que dans les cours d'eau, ne s'accordent pas avec les prédictions de la théorie de l'appariement des ressources. Une manipulation de la densité de C. aleuticus montre que l'estuaire pourrait contenir au moins deux fois plus d'individus qu'il n'y en a actuellement; ainsi l'estuaire, un habitat plus avantageux, est sous-utilisé. La compétition interspécifique avec C. asper est en partie responsable de cette sous-utilisation; en effet, des manipulations expérimentales qui comparent les effets intraspécifiques et interspécifiques montrent une réduction substantielle de la croissance et de la condition chez C. aleuticus. Le chevauchement spatial observé entre ces deux cottidés en plus des résultats des expériences sur la compétition laissent croire que C. aleuticus est plus limité dans sa capacité à utiliser de façon opportuniste les habitats de l'estuaire par la compétition interspécifique que par la compétition intraspécifique.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: April 1, 2005

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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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