Sources of variability and comparability between salmonid stomach contents and isotopic analyses: study design lessons and recommendations

نویسندگان

  • Mark R. Vinson
  • Phaedra Budy
چکیده

We compared sources of variability and cost in paired stomach content and stable isotope samples from three salmonid species collected in September 2001–2005 and describe the relative information provided by each method in terms of measuring diet overlap and food web study design. Based on diet analyses, diet overlap among brown trout, rainbow trout, and mountain whitefish was high, and we observed little variation in diets among years. In contrast, for sample sizes n ‡ 25, 95% confidence interval (CI) around mean d15N and d13C for the three target species did not overlap, and species, year, and fish size effects were significantly different, implying that these species likely consumed similar prey but in different proportions. Stable isotope processing costs were US$12 per sample, while stomach content analysis costs averaged US$25.49 ± $2.91 (95% CI) and ranged from US$1.50 for an empty stomach to US$291.50 for a sample with 2330 items. Precision in both d15N and d13C and mean diet overlap values based on stomach contents increased considerably up to a sample size of n = 10 and plateaued around n = 25, with little further increase in precision. Résumé : Nous avons comparé les sources de variabilité et les coûts dans des échantillons appariés de contenus stomacaux et d’isotopes stables récoltés en septembre 2001–2005 chez trois espèces de salmonidés; nous décrivons l’information relative apportée par chaque méthode en ce qui a trait au chevauchement des régimes alimentaires et au plan d’étude des réseaux trophiques. D’après les analyses des régimes alimentaires, le chevauchement est élevé entre la truite brune, la truite arc-en-ciel et le ménomini de montagnes et il y a peu de variation de régime entre les années. En revanche, pour des tailles d’échantillon de n ‡ 25, les intervalles de confiance (IC) à 95 % autour des valeurs moyennes de d15N et de d13C pour les trois espèces ciblées ne se chevauchent pas et les effets de l’espèce, de l’année et de la taille du poisson sont significativement différents, ce qui implique que ces espèces consument vraisemblablement des proies semblables, mais dans des proportions différentes. Le coût de traitement des analyses d’isotopes stables est de 12 $US par échantillon, alors qu’une analyse de contenu stomacal coûte en moyenne 25,49 ± 2,91 $US (IC à 95 %) et varie de 1,50 $US pour un tube digestif vide à 291,50 $US pour un échantillon contenant 2330 proies. La précision du chevauchement moyen des régimes alimentaires basé sur les valeurs de d15N et de d13C et sur les contenus stomacaux augmente considérablement jusqu’à une taille d’échantillon de n = 10 et atteint un plateau vers n = 25 avec peu d’augmentation de précision par la suite. [Traduit par la Rédaction]

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تاریخ انتشار 2010