Temporal variation in the niche partitioning of Lake Michigan salmonines as it relates to alewife abundance and size structure

Stable isotope analyses offer a useful means for quantifying ecological niche dimensions, though few studies have examined isotopic response of an ecological community with respect to resource gradients such as fluctuations in prey availability. Stable carbon and nitrogen isotopes were measured for Lake Michigan salmonines and their prey collected from 2014 to 2016. Bayesian ellipse and mixing model analyses were used to quantify isotopic niche characteristics and diets, respectively, among species and years. During the 3-year study period, abundance and size structure of preferred alewife (Alosa pseudoharengus) prey changed substantially and offered an opportunity to explore predator isotopic niche response and diet shifts along a prey resource gradient. Results suggested increased reliance on alewives, especially small alewives, over the study period and were consistent with greater availability of this prey. However, differential use of alewife size classes and alternative prey sources by salmonine predators was apparent, which suggested possible resource partitioning. Characterization of ecological niche overlap using stable isotopes likely requires consideration of shared resource availability as well as specific prey and habitat preferences. Si les analyses d'isotopes stables constituent une approche utile pour quantifier les dimensions de niches ecologiques, peu d'etudes se sont penchees sur la reaction isotopique d'une communaute ecologique en fonction de gradients de ressources tels que les fluctuations de la disponibilite de proies. Des isotopes stables du carbone et de l'azote ont ete mesures pour des salmonines du lac Michigan et leurs proies, preleves de 2014 a 2016. Des analyses d'ellipses bayesiennes et de modeles de melange ont ete utilisees pour quantifier les caracteristiques des niches isotopiques et les regimes alimentaires, respectivement, des differentes especes et d'une annee a l'autre. Durant la periode de trois ans qu'a dure l'etude, l'abondance et la structure de tailles de la proie de predilection, le gaspareau (Alosa pseudoharengus), ont considerablement change, ce qui offre l'occasion d'examiner la reaction des niches isotopiques et les changements des regimes alimentaires des predateurs le long d'un gradient de ressources de proies. Les resultats indiqueraient l'augmentation du recours aux gaspareaux, particulierement les petits gaspareaux, durant la periode d'etude et concordent avec une disponibilite accrue de ces proies. Des variations de l'utilisation de gaspareaux de differentes classes de tailles et d'autres sources de proies par les predateurs salmonines ressortent toutefois, qui indiqueraient un possible partage differentiel des ressources. La caracterisation du chevauchement des niches ecologiques a l'aide d'isotopes stables necessite probablement la prise en consideration de la disponibilite des ressources partagees, ainsi que des preferences en matiere de proies et d'habitats des differentes especes. [Traduit par la Redaction]
Introduction A growing number of studies have attempted to use stable isotope analyses to quantify multiple dimensions of an organism's ecological niche (e.g., Kornis et al. 2020; Layman et al. [...]