Carbon and nitrogen stable isotope (δ13C and δ15N) values of individual P. antipodarum and G. deflectus snails, and their primary diet sources in Spirit Lake. Periphyton and macrophyte ellipses defined by means ± standard deviations. Snail δ13C and δ15N values have been adjusted to account for isotopic trophic differences (mean ∆13Csnail-diet = 1.5‰, mean ∆15Nsnail-diet = 1.3‰, Li et al. 2018). The two snail species have overlapping distributions of ∆13Csnail-diet and ∆15Nsnail-diet values [MANOVA; Pillai = 0.0068425, approx. F1,27 = 0.089565, p>0.05].