Division of Biological Sciences, University of California at San Diego, La Jolla, CA 92093, USA.
Oecologia. 2010 Nov;164(3):763-71. doi: 10.1007/s00442-010-1694-1. Epub 2010 Jun 25.
Studies of food webs often employ stable isotopic approaches to infer trophic position and interaction strength without consideration of spatio-temporal variation in resource assimilation by constituent species. Using results from laboratory diet manipulations and monthly sampling of field populations, we illustrate how nitrogen isotopes may be used to quantify spatio-temporal variation in resource assimilation in ants. First, we determined nitrogen enrichment using a controlled laboratory experiment with the invasive Argentine ant (Linepithema humile). After 12 weeks, worker δ(15)N values from colonies fed an animal-based diet had δ(15)N values that were 5.51% greater compared to colonies fed a plant-based diet. The shift in δ(15)N values in response to the experimental diet occurred within 10 weeks. We next reared Argentine ant colonies with or without access to honeydew-producing aphids and found that after 8 weeks workers from colonies without access to aphids had δ(15)N values that were 6.31% larger compared to colonies with access to honeydew. Second, we sampled field populations over a 1-year period to quantify spatio-temporal variability in isotopic ratios of L. humile and those of a common native ant (Solenopsis xyloni). Samples from free-living colonies revealed that fluctuations in δ(15)N were 1.6-2.4‰ for L. humile and 1.8-2.9‰ for S. xyloni. Variation was also detected among L. humile castes: time averaged means of δ(15)N varied from 1.2 to 2.5‰ depending on the site, with δ(15)N values for queens ≥ workers > brood. The estimated trophic positions of L. humile and S. xyloni were similar within a site; however, trophic position for each species differed significantly at larger spatial scales. While stable isotopes are clearly useful for examining the trophic ecology of arthropod communities, our results suggest that caution is warranted when making ecological interpretations when stable isotope collections come from single time periods or life stages.
研究食物网时，通常采用稳定同位素方法来推断营养位置和相互作用强度，而不考虑组成物种对资源同化的时空变化。我们使用实验室饮食处理和野外种群逐月采样的结果，说明了如何使用氮稳定同位素来量化蚂蚁资源同化的时空变化。首先，我们通过用入侵的阿根廷蚂蚁（Linepithema humile）进行的受控实验室实验确定了氮的富集。12 周后，喂食动物源饮食的蚁群工蚁的δ(15)N 值比喂食植物源饮食的蚁群高 5.51%。对实验饮食的响应导致 δ(15)N 值在 10 周内发生变化。我们接下来饲养有或没有蚜虫蜜露的阿根廷蚁群，发现没有蚜虫蜜露的蚁群中的工蚁的δ(15)N 值比有蚜虫蜜露的蚁群大 6.31%。其次，我们在一年的时间里对野外种群进行了采样，以量化 L. humile 和常见的本地蚂蚁（Solenopsis xyloni）的同位素比值的时空变异性。从自由生活的蚁群中采集的样本表明，L. humile 的δ(15)N 波动幅度为 1.6-2.4‰，S. xyloni 的δ(15)N 波动幅度为 1.8-2.9‰。L. humile 的不同等级也存在差异：δ(15)N 的时间平均均值因地点而异，范围为 1.2 至 2.5‰，其中蚁后的δ(15)N 值大于工蚁>幼蚁。在一个地点内，L. humile 和 S. xyloni 的估计营养位置相似；然而，在更大的空间尺度上，每种物种的营养位置差异显著。虽然稳定同位素显然对研究节肢动物群落的营养生态很有用，但我们的结果表明，在从单一时间段或生命阶段收集稳定同位素时，在进行生态解释时应谨慎行事。
