QUANTITATIVE FATTY ACID SIGNATURE ANALYSIS: A NEW METHOD OF ESTIMATING PREDATOR DIETS

• Published in: Ecological Monographs
• Main Authors: Iverson, Sara J., Field, Chris, Don Bowen, W., Blanchard, Wade
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2004
• Subjects: Phoca groenlandica; Phoca vitulina
• Online Access: http://dx.doi.org/10.1890/02-4105; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1890%2F02-4105; https://esajournals.onlinelibrary.wiley.com/doi/pdf/10.1890/02-4105

Accurate estimates of the diets of predators are required in many areas of ecology, but for many species current methods are imprecise, limited to the last meal, and often biased. The diversity of fatty acids and their patterns in organisms, coupled with the narrow limitations on their biosynthesis, properties of digestion in monogastric animals, and the prevalence of large storage reservoirs of lipid in many predators, led us to propose the use of quantitative fatty acid signature analysis (QFASA) to study predator diets. We present a statistical model that provides quantitative estimates of the proportions of prey species in the diets of individual predators using fatty acid signatures. We conducted simulation studies using a database of 28 prey species ( n = 954 individuals) from the Scotian Shelf off eastern Canada to investigate properties of the model and to evaluate the reliability with which prey could be distinguished in the model. We then conducted experiments on grey seals ( Halichoerus grypus , n = 25) and harp seals ( Phoca groenlandica , n = 5) to assess quantitative characteristics of fatty acid deposition and to develop calibration coefficients for individual fatty acids to account for predator lipid metabolism. We then tested the model and calibration coefficients by estimating the diets of experimentally fed captive grey seals ( n = 6, switched from herring to a mackerel/capelin diet) and mink kits ( Mustela vison , n = 46, switched from milk to one of three oil‐supplemented diets). The diets of all experimentally fed animals were generally well estimated using QFASA and were consistent with qualitative and quantitative expectations, provided that appropriate calibration coefficients were used. In a final case, we compared video data of foraging by individual free‐ ranging harbor seals ( Phoca vitulina , n = 23) fitted with Crittercams and QFASA estimates of the diet of those same seals using a complex ecosystem‐wide prey database. Among the 28 prey species in the database, QFASA estimated ...