Fig 1.
Schematic illustrating the concept for determining trophic position of the carcass.
1) Blow fly larvae develop on a carcass (e.g., a deer) by consuming the animal’s tissue. 2) Larvae leave the carcass in order to pupate in the soil. 3) Adult blow flies emerge from puparia approximately 2 weeks after initial pupation and begin the free-roaming stage of their life cycle. 4) Analysis of a random adult blow fly can reveal the trophic position of the animal on which it developed as a larva. Different colors represent different carcass trophic positions and thus the variable isotopic signatures present within wild populations of adult blow flies. In the example illustrated here, the adult blow fly retains the δ15N value of the carcass (“herbivore”) from its larval stage.
Table 1.
Summary of isotopic data from the preservation experiment.
Fig 2.
Boxplots summarizing the fractionation values for all experiments.
Mean nitrogen fractionation (Δδ15N; panel A) and mean carbon fractionation (Δδ13C; panel B) are illustrated for each treatment across experiments. Open circles represent females and closed circles represent males. The red line indicates the mean value for both Δδ15N and Δδ13C across all experiments.
Fig 3.
Scatterplot of δ15N and δ13C values for the persistence of larval diet experiment.
Isotope relationships observed in this experiment demonstrate the possible range of fractionations during larval uptake. Circled clusters of data represent adult flies that were reared on their respective larval diets: chicken liver (blue), beef liver (grey), or salmon filet (green).
Table 2.
Summary of isotopic data from feeding experiments.
Table 3.
Ranges of δ15N values for each vertebrate trophic position obtained from the literature review.
Fig 4.
Putative carcass trophic values transformed from wild fly data by mean experimental fractionation factors for females.
Panel A: Proportion (out of 100%) of wild flies from urban, Smokies, and Yellowstone regions with isotopic signatures indicative of four carcass trophic positions: herbivore (green), herbivore/carnivore (grey), carnivore (orange), fish (blue). Panel B: Summary of results from wild flies are illustrated via scatterplot with δ15N given on the y-axis and δ13C values on the x-axis. Black circles = flies from the Great Smoky Mountains National Park; grey triangles = flies from the urban environment (Indianapolis, IN, USA); black X’s = flies from Yellowstone National Park.
Table 4.
Summary of blow fly sampling sites per region.