Department of Biology, California State University Dominguez Hills,1000 E Victoria St Carson, CA 90747, USA.
BMC Ecol. 2009 Nov 24;9:23. doi: 10.1186/1472-6785-9-23.
The isotopic composition of generalist consumers may be expected to vary in space as a consequence of spatial heterogeneity in isotope ratios, the abundance of resources, and competition. We aim to account for the spatial variation in the carbon and nitrogen isotopic composition of a generalized predatory species across a 500 ha. tropical rain forest landscape. We test competing models to account for relative influence of resources and competitors to the carbon and nitrogen isotopic enrichment of gypsy ants (Aphaenogaster araneoides), taking into account site-specific differences in baseline isotope ratios.
We found that 75% of the variance in the fraction of 15N in the tissue of A. araneoides was accounted by one environmental parameter, the concentration of soil phosphorus. After taking into account landscape-scale variation in baseline resources, the most parsimonious model indicated that colony growth and leaf litter biomass accounted for nearly all of the variance in the delta15N discrimination factor, whereas the delta13C discrimination factor was most parsimoniously associated with colony size and the rate of leaf litter decomposition. There was no indication that competitor density or diversity accounted for spatial differences in the isotopic composition of gypsy ants.
Across a 500 ha. landscape, soil phosphorus accounted for spatial variation in baseline nitrogen isotope ratios. The delta15N discrimination factor of a higher order consumer in this food web was structured by bottom-up influences - the quantity and decomposition rate of leaf litter. Stable isotope studies on the trophic biology of consumers may benefit from explicit spatial design to account for edaphic properties that alter the baseline at fine spatial grains.
由于同位素比值、资源丰度和竞争在空间上存在异质性，一般消费者的同位素组成可能会在空间上发生变化。我们旨在解释一种广泛的掠食性物种的碳和氮稳定同位素组成在 500 公顷热带雨林景观中的空间变化。我们测试了竞争模型，以解释资源和竞争者对吉普赛蚂蚁（Aphaenogaster araneoides）碳和氮稳定同位素富集的相对影响，同时考虑了基线同位素比值的特定地点差异。
我们发现，吉普赛蚂蚁组织中 15N 分数的方差有 75%可以用一个环境参数来解释，即土壤磷浓度。在考虑了景观尺度上基线资源的变化后，最简约模型表明，蚁群的生长和落叶生物量几乎可以解释 15N 同位素分馏因子的所有方差，而 13C 同位素分馏因子则与蚁群大小和落叶分解率最相关。没有迹象表明竞争者密度或多样性解释了吉普赛蚂蚁稳定同位素组成的空间差异。
在 500 公顷的景观中，土壤磷解释了基线氮同位素比值的空间变化。这个食物网中更高层次消费者的 15N 同位素分馏因子是由底层的影响结构决定的——落叶的数量和分解率。对消费者的营养生物学进行稳定同位素研究可能会受益于明确的空间设计，以解释改变细空间颗粒基线的土壤特性。
