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Ontogenetic niche shifts and resource partitioning of lake trout morphotypes

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Resource polymorphisms are widely observed in fishes; however, ontogenetic contributions to morphological and ecological differences are poorly understood. This study examined whether ontogenetic changes in niche partitioning could explain morphological and buoyancy differences between lake trout (Salvelinus namaycush) morphotypes in Great Slave Lake (Northwest Territories, Canada). Morphometric analysis, buoyancy, capture depth, diet, and stable isotope data were used in concert to determine whether (i) differences occur in small, as well as large, lake trout, (ii) ontogenetic changes in morphology and buoyancy correlate with shifts in depth or diet, and (iii) a subset of small trout, putatively identified as “humpers”, are distinct from other morphotypes. Ontogenetic changes in lake trout morphology were associated with an ecological shift between benthic and pelagic feeding. Resource partitioning between lean and siscowet-like trout occurred within benthic (small trout) and pelagic (large trout) habitats. The humper subset did not differ from small siscowet-like trout. By combining multiple methods and an ontogenetic perspective, our study provides novel perspectives on resource polymorphisms in large, deep lakes and on existing interpretations of stable isotope data from large lakes in general.

Le polymorphisme des ressources est un phénomène fréquemment observé chez les poissons; cependant, les contributions ontogéniques aux différences morphologiques et écologiques restent mal comprises. Notre étude examine si les changements ontogéniques de partition de niche peuvent expliquer les différences de morphologie et de flottabilité entre les morphotypes de touladis dans le Grand Lac des Esclaves (Territoires du Nord-Ouest, Canada). Une analyse morphométrique, ainsi que des données sur la flottabilité, la profondeur de capture, le régime alimentaire et les isotopes stables, nous ont servi tout ensemble à déterminer (i) si les différences se retrouvent à la fois chez les touladis de petite et de grande taille, (ii) s’il y a une corrélation entre les changements de morphologie et de flottabilité et les modifications de profondeur ou de régime alimentaire et (iii) si un sous-ensemble de touladis de petite taille, présumés être des «bossus», se distingue des autres morphotypes. Les changements ontologiques chez les touladis sont associés à une modification de l’alimentation, de benthique à pélagique. La partition des ressources entre les touladis maigres et les touladis d’allure siscowet se produit dans les habitats benthiques (petits touladis) et pélagiques (grands touladis). Le sous-ensemble des bossus ne diffère pas des petits touladis de type siscowet. En combinant plusieurs méthodes et utilisant une approche ontogénique, notre étude offre des perspectives inédites sur le polymorphisme des ressources dans des lacs profonds de grande taille et sur les interprétations actuelles des données d’isotopes stables dans les grands lacs en général.

Document Type: Research Article

Publication date: 2009-06-01

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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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