Abstract：
Food webs are complex ecological networks that reveal species interactions and energy flow in ecosystems. Prevailing ecological knowledge on forested streams suggests that their food webs are based on allochthonous carbon, driven by a constant supply of organic matter from adjacent vegetation and limited primary production due to low light conditions. Extreme climatic disturbances can disrupt these natural ecosystem dynamics by altering resource availability, which leads to changes in food web structure and functioning. Here, we quantify the response of stream food webs to two major hurricanes (Irma and María, Category 5 and 4, respectively) that struck Puerto Rico in September 2017. Within two tropical forested streams (first and second order), we collected ecosystem and food web data 6 months prior to the hurricanes and 2, 9, and 18 months afterward. We assessed the structural (e.g., canopy) and hydrological (e.g., discharge) characteristics of the ecosystem and monitored changes in basal resources (i.e., algae, biofilm, and leaf litter), consumers (e.g., aquatic invertebrates, riparian consumers), and applied Layman\'s community-wide metrics using the isotopic composition of 13 C and 15 N. Continuous stream discharge measurements indicated that the hurricanes did not cause an extreme hydrological event. However, the sixfold increase in canopy openness and associated changes in litter input appeared to trigger an increase in primary production. These food webs were primarily based on terrestrially derived carbon before the hurricanes, but most taxa (including Atya and Xiphocaris shrimp, the consumers with highest biomass) shifted their food source to autochthonous carbon within 2 months of the hurricanes. We also found evidence that the hurricanes dramatically altered the structure of the food web, resulting in shorter (i.e., smaller food-chain length), narrower (i.e., lower diversity of carbon sources) food webs, as well as increased trophic species packing. This study demonstrates how hurricane disturbance can alter stream food webs, changing the trophic base from allochthonous to autochthonous resources via changes in the physical environment (i.e., canopy defoliation). As hurricanes become more frequent and severe due to climate change, our findings greatly contribute to our understanding of the mechanisms that maintain forested stream trophic interactions amidst global change.
摘要：
食物网是复杂的生态网络，揭示了生态系统中物种的相互作用和能量流动。关于森林溪流的普遍生态知识表明，它们的食物网基于异源碳，由来自邻近植被的有机物质的恒定供应和由于弱光条件而导致的初级生产有限的驱动。极端的气候干扰可以通过改变资源的可用性来破坏这些自然生态系统的动态，这导致食物网结构和功能的变化。这里,我们量化了流食物网对两个主要飓风(Irma和María，分别为5类和4类），于2017年9月袭击波多黎各。在两条热带森林溪流中（一阶和二阶），我们在飓风发生前6个月和之后2、9和18个月收集了生态系统和食物网数据。我们评估了结构(例如，树冠)和水文(例如，排放)生态系统的特征和监测的基础资源变化(即，藻类,生物膜，和落叶)，消费者(例如，水生无脊椎动物,河岸消费者)，并使用13C和15N的同位素组成应用了Layman的全社区指标。连续流排放测量表明，飓风没有引起极端水文事件。然而,冠层开放的六倍增加和相关的垃圾输入变化似乎引发了初级生产的增加。这些食物网主要基于飓风之前的陆地碳，但是大多数类群(包括阿提亚和西菲卡利斯虾，生物量最高的消费者）在飓风发生后的2个月内将食物来源转移到了自生碳。我们还发现了飓风极大地改变了食物网结构的证据，导致更短(即，较小的食物链长度)，较窄(即，碳源多样性较低)食物网，以及增加营养物种包装。这项研究证明了飓风干扰如何改变溪流食物网，通过物理环境的变化将营养基础从异源资源改变为本地资源(即，冠层落叶)。由于气候变化，飓风变得更加频繁和严重，我们的发现极大地有助于我们理解在全球变化中维持森林河流营养相互作用的机制。
