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Table 1

Mean differences in δ13C and δ15N between fin and muscle values, and linear models (equations, 95% confidence intervals (95% CI) of the estimate and the intercept) fitting muscle δ13C and δ15N as a function of the isotope ratios in fin tissue for each species or group of species (anuran tadpoles and urodele adults). δ13C values were corrected for the lipid content according to Caut et al. (2013). The significance of the mean differences and linear equations is indicated: NS: non-significant, *p ≤ 0.05, **p < 0.01, ***p < 0.001.

Species N Mean difference (fin –muscleraw) Linear model

      Equations ±95% CI estimate ±95% CI intercept Adj. r²
δ13C            
Agile frog 29 0.44 ± 0.28*** δ13Cmuscle = 0.85 × δ13Cfin –5.50*** 0.13 4.39 0.86
European tree frog 14 0.19 ± 0.20** δ13Cmuscle = 0.87 × δ13Cfin –4.80*** 0.19 6.64 0.89
Marbled newt 30 –0.13 ± 0.36 NS δ13Cmuscle = 0.70 × δ13Cfin –7.43*** 0.18 4.64 0.68
Palmate newt 25 –1.44 ± 0.86*** δ13Cmuscle = 0.71 × δ13Cfin –7.03*** 0.17 4.65 0.77
Anuran tadpoles 43 0.36 ± 0.28*** δ13Cmuscle = 0.86 × δ13Cfin –5.01*** 0.07 2.15 0.95
Urodele adults 55 –0.73 ± 0.91*** δ13Cmuscle = 0.65 × δ13Cfin –8.57*** 0.07 1.74 0.89
             
δ15N            
Agile frog 29 –0.04 ± 0.36 NS δ15Nmuscle = 0.86 × δ15Nfin + 0.97*** 0.07 0.46 0.96
European tree frog 14 –0.84 ± 0.30*** δ15Nmuscle = 1.04 × δ15Nfin + 0.67** 0.43 1.77 0.67
Marbled newt 30 0.37 ± 0.45*** δ15Nmuscle = 1.01 × δ15Nfin –0.48*** 0.13 0.04 0.91
Palmate newt 25 0.43 ± 0.95* δ15Nmuscle = 0.89 × δ15Nfin + 0.40*** 0.15 1.19 0.86
Anuran tadpoles 43 –0.30 ± 0.51*** δ15Nmuscle = 0.79 × δ15Nfin + 1.54*** 0.06 0.36 0.95
Urodele adults 55 0.40 ± 0.72*** δ15Nmuscle = 0.92 × δ15Nfin + 0.18*** 0.10 0.73 0.87