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

长期的环境研究提供了短期努力所缺乏的背景。在较长时期内收集的数据使研究人员能够量化短暂或偶发因素的影响，这些因素只是逃避短期努力。该项目始于1989年，最初是对智利博斯克·弗雷·豪尔赫国家公园半干旱灌木丛群落中生物相互作用的重要性进行的实验研究。虽然早些年记录了捕食的作用，但在工作的第一个十年，间歇性降雨(特别是与厄尔尼诺现象有关的降雨)的压倒性作用变得明显。在第二和第三个十年中，这项研究的重点是生物和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。该项目现在是同类项目中运行时间最长的试验田研究项目，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能量流动(从植物通过消费者到捕食者)作为降雨和水文条件的函数的新颖和复杂的评估，以及对长期种群动态的高级建模，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。在这个网站收集的数据将被用来改善对国家公园和周围地区自然历史和生态的推广工作，也将被纳入IsoCamp(isocamp.org)，这是一个为期两周的关于稳定同位素生物地球化学和生态学的短期课程，面向研究生和博士后研究人员。该项目以20个实验网格(75x75米)为中心，其中包括以下活动：(1)每月(4天/月)采样小型哺乳动物；(2)每三个月测量灌木覆盖率，在生长季节每月测量短暂植物的覆盖率；(3)每4个月采集一次土壤样本，以估计种子密度；(4)每月从工地和附近的栖息地收集狐狸粪便和猫头鹰颗粒，以确定它们的饮食特征。虽然排除一种小型哺乳动物食草动物(DECU)的影响有限，但2002年实施的全部小型哺乳动物排除措施对几个植物物种显示出强烈的影响。叠加在这些影响之上的是植物、小型哺乳动物和捕食者对8次厄尔尼诺/高降雨事件期间降水增加的戏剧性反应。智利中北部经历了十多年的严重干旱，但天气预报员预测厄尔尼诺现象将更加频繁和强烈，这表明非生物条件下的极端时间变化。该项目将继续跟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元编码和经验动态建模的新集成，以更好地描述营养结构如何受到时间变化的能量流的影响。未来5年的主要焦点包括：(1)入侵沼泽的存在和丰富如何影响植物和小型哺乳动物？(2)快速生长的短命草本植物和生长缓慢的多年生灌木的可用性的变化如何影响小型哺乳动物的食物广度和生态位分配？(3)在种群繁荣-萧条周期中，杂食性动物是否促进了个体和种群水平的生态位分配？(4)多通道能量流动和营养结构的时间变化如何影响小型哺乳动物群落的稳定性？这些目标是通过与智利和美国多个机构的多名调查人员广泛合作来实现的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.