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AUTHORS: Austin Happel, Illinois Natural History Survey; Jeremy Pike, The College at Brockport; Sergiusz Czesny, Illinois Natural History Survey; Jacques Rinchard, The College at Brockport
ABSTRACT: Biochemical methods of describing diets have become common place in ecological studies.Recently, models have been developed to explore the potential of quantifying diet compositions using fatty acid profiles. Current theory is that wild individuals can be compared to the fatty acid profiles of consumers fed known diets using quantitative models to estimate their diet compositions. We set out to empirically test this idea through a novel feeding experiment using natural prey species. Our hypothesis was: If fatty acid profiles reflect dietary origins, then computer models could be used to predict components of a known diet fed to fishes. Using three different freeze-dried prey species, we generated diets consisting of various prey compositions that were fed to Lake Trout for periods of 8 and 12 weeks. Neither quantitative model performed as well as expected based on previous applications, despite using data from a controlled feeding experiment that qualitatively met expectations when viewed through nMDS. For reasons that are complex, mixed diets assimilated into Lake Trout in patterns that are less predictable than expected. We could not find any consistencies with growth indices or lipid accrual, but suspect that sampling specific lipid fractions or tissues would be more accurate than our results using whole body lipids indicate. We conclude that quantitative models using fatty acid profiles likely perform well at describing large differences in foraging habits, but may not provide accurate data on minute variations in diet compositions of fishes.
