Collaborative Research: LTREB: Experimental determination of trophic dynamics and energy flows in a semiarid habitat in Chile

长期环境研究提供了短期努力所缺乏的背景。在较长时间内收集的数据使研究人员能够量化短期努力无法实现的短暂或偶然因素的影响。该项目始于1989年，当时是对智利博格斯弗赖豪尔赫国家公园半干旱刺丛群落中生物相互作用重要性的实验调查。虽然在早期就记录了捕食的作用，但在第一个十年的工作中，偶发性降雨（特别是El Niño-associated降雨）的压倒性作用变得清晰起来。在第二和第三个十年中，研究的重点是生物与非生物影响的相对作用，入侵计划和兔子的作用，以及长期干旱条件的影响。该项目是同类实验中运行时间最长的实地研究项目，它记录了小型哺乳动物食草性的显著但有限的影响，以及入侵物种和降雨（及其缺失）对植物和小型哺乳动物种群的显著影响。目前的研究增加了对降雨和水文条件下能量流动（从植物到消费者到捕食者）的新颖和复杂的评估，以及对长期种群动态的先进建模，以确定在这个高度可变的系统中观察到的群落稳定性变化的潜在机制。在该站点收集的数据将用于改善国家公园及周边地区自然历史和生态方面的推广工作，也将被纳入IsoCamp (isocamp.org)，这是一个为研究生和博士后研究人员提供的为期两周的稳定同位素生物地球化学和生态学短期课程。本项目以20个实验网格（75x75 m）为中心，进行以下活动：(1)每月取样小型哺乳动物（4天/月）；(2)灌木覆盖度每3个月测量一次，短命植物覆盖度在生长季节每月测量一次；(3)每4个月采集土壤样品估算种子密度；(4)每月从现场和附近的栖息地收集狐狸的粪便和猫头鹰的颗粒，以确定它们的饮食特征。尽管排除一种小型食草哺乳动物（德古）的影响有限，但2002年对所有小型哺乳动物的排除表明，对几种植物物种有很强的影响。在8el Niño/高降雨事件期间，植物、小型哺乳动物和食肉动物对降水增加的剧烈反应叠加在这些影响之上。十多年来，智利中北部经历了严重的干旱，但预报员预测，厄尔尼诺Niño事件将更加频繁和强烈，这表明非生物条件的极端时间变化。该项目将继续追踪环境变化和入侵物种的相互作用，但增加了稳定同位素、粪便DNA元条形码和经验动态建模的新整合，以更好地表征营养结构如何受到时间变化的能量流的影响。未来5年的重点研究方向包括：(1)植物和小型哺乳动物如何受到外来物的影响？(2)快速生长的短生草本植物和缓慢生长的多年生灌木的可利用性变化如何影响小型兽类的饮食宽度和生态位分配？(3)在种群盛衰周期中，杂食性是否促进了个体和种群水平的生态位划分？(4)多通道能量流和营养结构的时间变化如何影响小哺乳动物群落的稳定性？这些目标正在通过与智利和美国多个机构的多名研究人员的广泛合作来实现。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Long-term environmental research provides context that shorter-term efforts lack. Data collected over extended periods allows researchers to quantify the influence of fleeting or episodic factors that simply elude short-term efforts. This project started in 1989 as an experimental investigation of the importance of biotic interactions in a semiarid thorn scrub community in Bosque Fray Jorge National Park, Chile. While a role of predation was documented in early years, the overwhelming role of episodic rainfall (especially El Niño-associated rains) became clear in the first decade of work. Through the second and third decades the study focused on the relative role of biotic vs. abiotic influences, the role of invasive plans and rabbits, and the impact of extended drought conditions. Now the longest-running experimental field research program of its kind, this project has documented significant but limited effects of small mammal herbivory, and significant effects of invasive species and rainfall (and its absence) on populations of both plants and small mammals. The current research adds novel and sophisticated assessment of energy flow (from plants through consumers to predators) as a function of rainfall and hydrologic conditions, and advanced modeling of long-term population dynamics to identify mechanisms underlying changes in community stability observed in this highly variable system. Data collected at this site will be used to improve outreach efforts on the natural history and ecology of the National Park and the surrounding region, and will also be included in IsoCamp (isocamp.org), a two-week short course on stable isotope biogeochemistry and ecology for graduate students and postdoctoral researchers.This project is centered on 20 experimental grids (75x75 m) in which the following activities occur: (1) small mammals are sampled monthly (4 days/month); (2) cover by shrubs is measured every three months, and that of ephemeral plants monthly during the growing season; (3) soil samples are taken every 4 months to estimate seed density; and (4) fox scat and owl pellets are collected monthly from the site and nearby roosts to characterize their diets. Whereas exclusions of one small mammal herbivore (the degu) had limited effects, installation of all‐small mammal exclusions in 2002 demonstrated strong effects on several plant species. Superimposed on these effects were dramatic responses of plants, small mammals, and predators to increased precipitation during 8 El Niño/high rainfall events. North-central Chile has experienced severe drought conditions for over a decade, but forecasters predict more frequent and intense El Niño events, suggesting extreme temporal variation in abiotic conditions. This project will continue to track the interactive roles of environmental change and invasive species, but adds novel integration of stable isotopes, fecal DNA metabarcoding, and empirical dynamic modeling to better characterize how trophic structure is influenced by temporally varying energy flows. Key foci over the next 5 years include: (1) How are plants and small mammals influenced by the presence and abundance of invasive lagomorphs?; (2) How does variation in the availability of fast-growing ephemeral herbs and slow-growing perennial shrubs influence dietary breadth and niche partitioning among small mammals?; (3) Does omnivory facilitate individual- and population-level niche partitioning during boom-bust population cycles?; (4) How does multichannel energy flow and temporal variation in trophic structure affect small mammal community stability? These goals are being pursued through extensive collaboration with multiple investigators at multiple institutions in Chile and the United States.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.