Aquatic Station, Department of Biology, Texas State University, San Marcos, TX, 78666, USA.
Texas Fish and Wildlife Conservation Office, US Fish and Wildlife Service, San Marcos, TX, 78666, USA.
Oecologia. 2021 May;196(1):235-248. doi: 10.1007/s00442-021-04912-z. Epub 2021 Apr 7.
Spring orifices are ecotones between surface and subterranean aquatic ecosystems. Invertebrates of different origins (e.g., surface, spring obligate, and subterranean) coexist in these spatially restricted environments, potentially competing for resources. However, processes that allow for population coexistence in these presumably low resource environments are not well understood. We examined invertebrate communities at two spring complexes in Texas, USA and assessed resource use and food web structure at spring orifices using stable isotopes of carbon (δC) and nitrogen (δN). Using bulk δC and δN of organisms and potential food sources, we elucidated dietary sources and found that invertebrate communities exhibited resource partitioning and contained two main food chains (periphyton versus terrestrial organic matter [OM]). In both spring complexes, several endemic spring orifice associated and subterranean taxa derived most of their diet from terrestrial OM. Analysis of compound-specific stable isotopes (i.e., δC of essential amino acids, EAAs) from two co-occurring elmid species indicated that the endemic spring orifice-associated species (Heterelmis comalensis) derived > 80% of its EAAs from bacteria, whereas the widespread surface species (Microcylloepus pusillus) derived its EAAs from a more equitable mix of bacteria, fungi, and algae. We additionally calculated niche overlap among of several taxonomically related groups (aquatic beetles and amphipods) that co-occur in spring ecotones and posterior probability estimates indicated little to no niche overlap among related species. Results indicate that invertebrates at subterranean-surface aquatic ecotones are partitioning food resources and highlight the importance of connections to riparian zones for persistence of several endemic invertebrates.
春孔是地表水和地下水生生态系统之间的生态过渡带。不同来源的无脊椎动物（如地表水、春孔专性和地下）共存于这些空间受限的环境中，可能会争夺资源。然而，在这些资源匮乏的环境中，允许种群共存的过程尚不清楚。我们在美国德克萨斯州的两个泉眼复合体中检查了无脊椎动物群落，并使用碳（δC）和氮（δN）的稳定同位素评估了泉眼的资源利用和食物网结构。使用生物体和潜在食物源的总 δC 和 δN，我们阐明了饮食来源，并发现无脊椎动物群落表现出资源分区，包含两条主要的食物链（周丛生物与陆地有机物质 [OM]）。在两个泉眼复合体中，有几个特有泉眼相关和地下分类群的大部分食物来源都来自陆地 OM。两种共生的摇蚊科物种的特定化合物稳定同位素（即必需氨基酸的 δC，EAAs）分析表明，特有泉眼相关物种（Heterelmis comalensis）的 EAAs 有>80%来自细菌，而广泛分布的地表水物种（Microcylloepus pusillus）的 EAAs 则来自于细菌、真菌和藻类的更均衡的混合。我们还计算了在泉眼生态过渡带共存的几个分类相关群体（水生甲虫和等足类动物）之间的生态位重叠，并且后验概率估计表明相关物种之间几乎没有生态位重叠。结果表明，地下-地表水生生态过渡带的无脊椎动物正在对食物资源进行分区，并强调了与河岸带连接对于几种特有无脊椎动物的生存的重要性。
