Supporting data for tiger beetle stable isotope analysis

Stable isotope ratios give insight into food web interactions, but
interpretation can be clouded by dietary shifts and the associated timing
of isotopic change, as well as the difference in isotope ratios between
consumers and their diets at equilibrium. Typically, the 15N/14N ratio
(δ15N) increases with each trophic transfer as 15N becomes enriched,
whereas the 13C/12C ratio (δ13C) remains relatively constant with each
trophic transfer but can be influenced by the lipid content of the study
organism. This study reports the trophic discrimination factors and
isotopic half-lives in tiger beetles (Coleoptera: Cicindelidae) collected
near a large river in central Canada. Wild-caught tiger beetle larvae were
reared in a laboratory setting, subjected to a diet switch experiment, and
sampled over a period of 36 days. Quadratic plateau models were used to
characterize the change in δ15N, δ13C, and the lipid-corrected carbon
ratio (δ13Ccorr) over time, and trophic discrimination factors were
calculated by subtracting the mean prey δ15N, δ13C, and δ13Ccorr from that
of the tiger beetle asymptotic δ15N, δ13C, and δ13Ccorr values,
respectively. The tiger beetle trophic discrimination factor for δ15N was
1.7 ±0.2‰ with a half-life of 11.4 days. For δ13C, the trophic
discrimination factor and half-life were –0.6 ±0.2‰ and 3.9 days,
respectively. After correcting for lipids (δ13Ccorr), the trophic
discrimination factor was –0.2 ±0.2‰ with a half-life of 4.7 days. Our
findings show that isotopic turnover of carbon and nitrogen in tiger
beetles occurs relatively quickly and is comparable to rates reported for
other insects. The trophic discrimination factors and turnover rates
calculated in our study could be applied to future studies on wild tiger
beetles.