Giesbrecht Lesa S, Bell Aaron J, Jardine Timothy D, Prager Sean M, Phillips Iain D
Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
Troutreach Saskatchewan, Saskatchewan Wildlife Federation, Moose Jaw, Saskatchewan, Canada.
PeerJ. 2025 Apr 30;13:e19279. doi: 10.7717/peerj.19279. eCollection 2025.
Stable isotope ratios give insight into food web interactions, but interpretation can be clouded by the timing of isotopic change associated with changes in diet and the difference in isotope ratios between consumers and their diets at equilibrium. The N/N, deemed δN, increases with each trophic transfer as N becomes enriched, whereas the C/C ratio, denoted as δC, remains relatively constant with each trophic transfer but can be influenced by lipid content. This study reports the trophic discrimination factors and isotopic half-lives in tiger beetles (Coleoptera: Cicindelidae). Wild-caught tiger beetle larvae were reared in a laboratory setting, subjected to a diet switch experiment, and sampled over time. Quadratic plateau models were used to characterize the change in δN, δC, and δC over time. Trophic discrimination factors were calculated by subtracting the mean prey δN, δC, and δC from that of the tiger beetle asymptotic δN, δC and δC values, respectively. The tiger beetle trophic discrimination factor for δN was 1.7 ± 0.2‰ with a half-life of 11.4 days. For δC, the trophic discrimination factor and half-life were -0.6 ± 0.2‰ and 3.9 days, respectively. After correcting for lipids (δC), the trophic discrimination factor was -0.2 ± 0.2‰ with a half-life of 4.7 days. Isotopic turnover was fast with short half-lives, but factors that influence metabolic rates, such as ambient temperatures and life stage, should be considered when applying these estimates to wild tiger beetles. Despite this, the trophic discrimination factors and turnover rates calculated in this article are suitable estimates which can be applied to future studies.
稳定同位素比率有助于洞察食物网的相互作用，但由于与饮食变化相关的同位素变化时间以及消费者与其处于平衡状态时的饮食之间的同位素比率差异，其解释可能会受到影响。氮/氮比率，即δN，随着每次营养级传递而增加，因为氮会富集，而碳/碳比率，即δC，在每次营养级传递时保持相对恒定，但会受到脂质含量的影响。本研究报告了虎甲（鞘翅目：虎甲科）的营养级分馏因子和同位素半衰期。将野外捕获的虎甲幼虫在实验室环境中饲养，进行饮食转换实验，并随时间进行采样。使用二次平台模型来表征δN、δC和δC随时间的变化。通过分别从虎甲的渐近δN、δC和δC值中减去平均猎物的δN、δC和δC来计算营养级分馏因子。虎甲δN的营养级分馏因子为1.7±0.2‰，半衰期为11.4天。对于δC，营养级分馏因子和半衰期分别为-0.6±0.2‰和3.9天。在对脂质（δC）进行校正后，营养级分馏因子为-0.2±0.2‰，半衰期为4.7天。同位素周转很快，半衰期很短，但在将这些估计值应用于野生虎甲时，应考虑影响代谢率的因素，如环境温度和生命阶段。尽管如此，本文计算的营养级分馏因子和周转率是适用于未来研究的合适估计值。
