77.6 Friday, Jan. 6 Use of Stable Isotope Approaches to Study Spatial Variation in Diet: Rattlesnakes as a case study. PILGRIM, Melissa A.*; FARRELL, Terence M.; University of South Carolina Upstate; Stetson University email@example.com
We tested the validity of the stable isotope approach for determining differences in pigmy rattlesnake (Sistrurus miliarius) diet composition among three Florida populations. We collected scale clips from 186 rattlesnakes captured in the study populations (65 Hog Island individuals, 62 Jones Island individuals, and 59 Uplands individuals). We determined the stable carbon and nitrogen isotope ratios for each scale clip (δ13C values ranged from -18.1 to -23.9 and δ15N values ranged from 4.3 to 8.4). Hog Island average δ13C values (-20.8 ± 0.13) were significantly enriched relative to Jones Island and Uplands average δ13C values (-22.3 ± 0.13 and -22.1 ± 0.12, respectively). Average δ15N values of each population were significantly different from one another (Hog Island = 6.2 ± 0.08; Jones Island = 6.9 ± 0.07; Uplands = 5.8 ± 0.10). To evaluate what portion of the observed variation in scale tissue isotope values was related to differences in food sources, we built an isotopic profile of potential prey items for each population. We collected 992 prey items, representing 10 amphibian, 8 reptile and 7 mammal species. Prey δ13C values ranged from -31.1 to -14.5‰ and prey δ15N values ranged from 0.3 to 7.0‰. When trying to link observed variation in snake isotope values to differences in diet composition, our interpretations were complicated by spatial variation in prey abundance and within-species spatial variation in prey isotopic composition. Our work emphasizes that use of stable isotopes as trophic indicators in natural systems is most accurate when sources of variation in the isotopic baseline (i.e., food sources) of the system are quantified.