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本期阅读 @生态系统生态学 *仅供个人参考
2023-06-28 https:///10.1038/s43017-023-00454-5 背景 @生态系统生态学 土壤是生物圈的重要生物栖息地，不同的陆地生态系统过程相互作用。过去的气候和生物活动影响今天的土壤结构和组成，因此，土壤对现代自然扰动的反应取决于过去的环境和生态条件。这种现象是由土壤记忆的概念形式化的，其中土壤记录了过去影响的持久印记。过去的影响可能包括干旱、洪水、森林火灾和土地利用变化等外部因素，也可能包括土壤有机碳分解速率、土壤植物区系和动物种群规模及增长速率等内生驱动因素。由此产生的变化可能包括土壤状况(如水分和有机碳含量)和性状(如保水性和导水率)。最后，这些印记影响土壤和生态系统未来的通量和功能 由于土壤记忆将生态系统的功能和气候联系到一个跨越时间和空间的复杂适应性系统，它为研究过去事件对当前和未来地表反应的影响提供了一个途径。然而，土壤记忆的应用是难以捉摸的，并且仅限于模拟中的特定应用(例如，气候中的土壤湿度记忆)或特定学科(古生物学)。在这里，我们认为土壤记忆是代表地球系统动力学和陆地表面和气候共同进化的核心。准确预测陆地生态系统过程和解析陆面模式的气候特征是非常必要的。 土壤记忆的载体 @生态系统生态学 陆地表面模型（LSMs）忽略了土壤记忆 @生态系统生态学 在地球模型中纳入土壤记忆 @生态系统生态学 主要图表 @生态系统生态学
Reference(s) Rahmati, M., Or, D., Amelung, W. et al. Soil is a living archive of the Earth system. Nat Rev Earth Environ (2023). https:///10.1038/s43017-023-00454-5 生态系统生态学是生态学的一个分支学科，专注于研究生物体和它们在特定生态系统中的物理环境之间的相互作用。生态系统生态学研究能量和营养物质在生态系统中的流动、生态系统内不同物种之间的关系，以及生态系统如何应对长期以来的环境变化。生态系统生态学旨在了解生态系统中存在的复杂关系和反馈循环，以及它们如何促进生态系统的功能和稳定。通过研究生态系统的结构和功能，生态系统生态学家可以深入了解生态系统如何受到自然和人为干扰的影响，如气候变化，污染和栖息地破坏。生态系统生态学是一个高度跨学科的领域，吸收了来自生物学、地质学、化学、物理学和数学的概念和技术。生态系统生态学的最终目标是提供对生态系统如何工作的全面理解，并为旨在保护这些重要自然系统的管理和保护工作提供信息。全球气候变化是我们这个时代最紧迫的环境问题之一，因此在生态系统生态学中有几个热门话题与之相关。其中一些主题包括: 变暖温度对生态系统过程的影响: 随着温度继续上升，生态系统过程，如光合作用，呼吸和养分循环正在受到影响。研究人员正在研究生态系统过程中的这些变化将如何影响生态系统的功能和服务。物种分布范围和群落动态的变化: 随着气温的升高，许多物种的分布范围会随着气候条件的变化而变化。生态系统生态学家正在研究这些变化是如何影响物种相互作用和群落动态的。碳循环反馈: 生态系统在全球碳循环中发挥着至关重要的作用，气候变化引起的生态系统进程变化正在影响生态系统可以储存的碳量。研究人员正在研究这些变化将如何反馈到气候系统，潜在地加剧气候变化。极端天气事件的影响: 气候变化导致更频繁和更强烈的极端天气事件，如干旱、洪水和野火。生态系统生态学家正在研究这些事件是如何影响生态系统过程、生物多样性和生态系统服务的。管理和恢复战略: 鉴于气候变化对生态系统的影响，有必要制定管理和恢复战略，以维持生态系统的功能和服务。生态系统生态学家正在研究基于生态系统的适应等不同策略在减轻气候变化对生态系统影响方面的有效性。生态系统生态学的研究可以在几个方面与全球气候变化、碳氮循环和生物多样性丧失联系起来。这里有一些例子: 气候变化和生态系统过程: 气候变化通过改变温度和降水模式影响生态系统过程，如碳(C)和氮(N)循环。生态系统生态学家研究气候变化对这些过程的影响，以及它们如何反馈到气候系统中。碳氮循环与全球气候变化: 碳氮循环是全球碳氮循环的重要组成部分，对全球气候变化有重要影响。生态系统生态学家研究生态系统中碳和氮循环的速率和机制，以及它们如何受到气候变化的影响。生物多样性丧失和生态系统过程: 生物多样性丧失可以对生态系统过程产生重大影响，如养分循环、初级生产力和分解。生态系统生态学家研究生物多样性丧失对这些过程的影响，以及它们可能如何影响生态系统的功能和服务。基于生态系统的减缓气候变化方法: 基于生态系统的方法，如造林、再造林和生态系统恢复，可以通过固碳、加强生物多样性和改善生态系统功能，帮助减轻气候变化的影响。生态系统生态学家研究这些方法的有效性以及如何利用它们来应对气候变化。总的来说，生态系统生态学为理解生态系统、全球气候变化、碳氮循环以及生物多样性丧失之间复杂的相互作用提供了一个框架。通过研究这些相互作用，我们可以制定减轻气候变化影响和保护生态系统功能和服务的战略。 Ecosystem ecology is a sub-discipline of ecology that focuses on studying the interactions between living organisms and their physical environment in a particular ecosystem. Ecosystem ecology examines the flow of energy and nutrients through ecosystems, the relationships between different species within ecosystems, and how ecosystems respond to environmental changes over time. Ecosystem ecology aims to understand the complex relationships and feedback loops that exist within ecosystems and how they contribute to the functioning and stability of ecosystems. By studying the structure and function of ecosystems, ecosystem ecologists can gain insights into how ecosystems are affected by natural and human-induced disturbances, such as climate change, pollution, and habitat destruction. Ecosystem ecology is a highly interdisciplinary field that draws on concepts and techniques from biology, geology, chemistry, physics, and mathematics. The ultimate goal of ecosystem ecology is to provide a comprehensive understanding of how ecosystems work and to inform management and conservation efforts aimed at preserving these important natural systems. There are several hot topics in ecosystem ecology related to global climate change, as it is one of the most pressing environmental issues of our time. Some of these topics include: Impacts of warming temperatures on ecosystem processes: As temperatures continue to rise, ecosystem processes such as photosynthesis, respiration, and nutrient cycling are being affected. Researchers are studying how these changes in ecosystem processes will affect ecosystem functioning and services. Shifts in species ranges and community dynamics: As temperatures warm, many species are shifting their ranges in response to changing climatic conditions. Ecosystem ecologists are studying how these shifts are affecting species interactions and community dynamics. Carbon cycle feedbacks: Ecosystems play a crucial role in the global carbon cycle, and changes in ecosystem processes due to climate change are affecting the amount of carbon that ecosystems can store. Researchers are studying how these changes will feedback into the climate system, potentially exacerbating climate change. Impacts of extreme weather events: Climate change is leading to more frequent and intense extreme weather events such as droughts, floods, and wildfires. Ecosystem ecologists are studying how these events are affecting ecosystem processes, biodiversity, and ecosystem services. Management and restoration strategies: Given the impacts of climate change on ecosystems, there is a need to develop management and restoration strategies to maintain ecosystem functioning and services. Ecosystem ecologists are studying the effectiveness of different strategies, such as ecosystem-based adaptation, in mitigating the impacts of climate change on ecosystems. The research of ecosystem ecology can be connected to global climate change, C and N cycling, and biodiversity loss in several ways. Here are a few examples: Climate change and ecosystem processes: Climate change is affecting ecosystem processes such as carbon (C) and nitrogen (N) cycling by altering temperature and precipitation patterns. Ecosystem ecologists study the impacts of climate change on these processes and how they might feedback into the climate system. Carbon and nitrogen cycling and global climate change: Carbon and nitrogen cycling are important components of the global carbon and nitrogen cycles, which have significant impacts on global climate change. Ecosystem ecologists study the rates and mechanisms of C and N cycling in ecosystems and how they are affected by climate change. Biodiversity loss and ecosystem processes: Biodiversity loss can have significant impacts on ecosystem processes such as nutrient cycling, primary productivity, and decomposition. Ecosystem ecologists study the impacts of biodiversity loss on these processes and how they might affect ecosystem functioning and services. Ecosystem-based approaches to climate change mitigation: Ecosystem-based approaches such as afforestation, reforestation, and ecosystem restoration can help mitigate the impacts of climate change by sequestering carbon, enhancing biodiversity, and improving ecosystem functioning. Ecosystem ecologists study the effectiveness of these approaches and how they can be used to address climate change. Overall, ecosystem ecology provides a framework for understanding the complex interactions between ecosystems, global climate change, C and N cycling, and biodiversity loss. By studying these interactions, we can develop strategies for mitigating the impacts of climate change and preserving ecosystem functioning and services. 是什么赋予生命力量？阳光和营养物质是如何影响我们赖以生存的植物的？温室气体和其他污染物如何降解构成生态系统的植物、动物和微生物种群之间的相互作用？生态系统生态学是关于环境中有生命和无生命的组成部分的研究，这些因素如何相互作用，以及自然和人类引起的变化如何影响它们的功能。了解生态系统如何工作，首先要了解阳光如何转化为可用能源，营养循环的重要性，以及人类对环境的影响。植物将阳光转化为可利用的碳基能源形式。种群的初级生产力和次级生产力可以用来确定生态系统中的能量流动。研究大气的影响——二氧化碳将对未来的农业生产和食品质量产生影响。生态系统生态学的一个新焦点是气候变化。世界正在以惊人的速度发生变化，从某些地区的降水量增加到减少，从草原到沙漠(荒漠化)或从森林到草原(干旱增加)的生态系统正在发生变化。生态系统生态学家目前正在研究气候变化的原因和影响，希望有一天能尽量减少我们对地球的影响，并保护我们今天所知道的自然生态系统。为了丰富对生态系统生态学的理解，从这个介绍性的概述开始，然后探索你将在下面找到的其他概述。 What powers life? How do sunlight and nutrients affect the plants we depend on? How do greenhouse gases and other contaminants degrade the interactions among the plant, animal, and microbial populations that comprise ecosystems? Ecosystem ecology is the study of these and other questions about the living and nonliving components within the environment, how these factors interact with each other, and how both natural and human-induced changes affect how they function. Understanding how ecosystems work begins with an understanding of how sunlight is converted into usable energy, the importance of nutrient cycling, and the impact mankind has on the environment. Plants convert sunlight into usable forms of energy that are carbon based. Primary and secondary production in populations can be used to determine energy flow in ecosystems. Studying the effects of atmospheric? CO2 will have future implications for agricultural production and food quality. A new focus in ecosystem ecology has been climate change. The world is being altered at an alarming pace from greater to lesser precipitation in some areas to change in ecosystems from grasslands to desert (desertification) or forests to grasslands (increased aridity). Ecosystem ecologists are now studying the causes and effects of climate change, hoping to one day minimize our impact on the planet and preserve natural ecosystems as we know them today. To develop a rich understanding of ecosystems ecology, begin with this introductory overview, and then explore the other summaries you’ll find below. 生物多样性、稳定性和生态系统功能 气候变化和其他人类驱动的（人为的）环境变化将在未来几十年继续造成生物多样性的丧失（Sala等人，2000年），此外全球已经发生的物种灭绝率很高（Stork，2010年）。生物多样性是一个可以用来描述各种不同尺度的生物多样性的术语，但在这种情况下，我们将重点描述物种多样性。物种在生态系统中发挥着重要作用，因此当地和全球物种的损失可能威胁到人类赖以生存的生态系统服务的稳定性（McCann 2000）。例如，植物物种利用太阳的能量通过光合作用固定碳，而这一重要的生物过程为无数动物消费者提供了食物链的基础。在生态系统层面，所有植物物种的总生长都被称为初级生产，正如我们将在本文中看到的那样，由不同数量和组合的植物组成的群落可能具有非常不同的初级生产率。生态系统功能的这一基本指标与全球粮食供应和气候变化率有关，因为初级生产反映了二氧化碳（一种温室气体）从大气中去除的速度。目前，人们对自然和人类管理的生态系统的稳定性非常担忧，特别是考虑到已经发生的无数全球变化。稳定性可以用几种方式来定义，但稳定系统最直观的定义是，尽管环境条件不断变化，但其可变性很低（即与平均状态的偏差很小）。这通常被称为系统的阻力。弹性是稳定性的一个不同方面，表明生态系统在受到扰动或其他扰动后恢复原状的能力。 Introduction: Biodiversity, Stability, and Ecosystem Functioning Climate change and other human-driven (anthropogenic) environmental changes will continue to cause biodiversity loss in the coming decades (Sala et al. 2000), in addition to the high rates of species extinctions already occurring worldwide (Stork 2010). Biodiversity is a term that can be used to describe biological diversity at a variety of different scales, but in this context we will focus on the description of species diversity. Species play essential roles in ecosystems, so local and global species losses could threaten the stability of the ecosystem services on which humans depend (McCann 2000). For example, plant species harness the energy of the sun to fix carbon through photosynthesis, and this essential biological process provides the base of the food chain for myriad animal consumers. At the ecosystem level, the total growth of all plant species is termed primary production, and — as we'll see in this article — communities composed of different numbers and combinations of plant species can have very different rates of primary production. This fundamental metric of ecosystem function has relevance for global food supply and for rates of climate change because primary production reflects the rate at which carbon dioxide (a greenhouse gas) is removed from the atmosphere. There is currently great concern about the stability of both natural and human-managed ecosystems, particularly given the myriad global changes already occurring. Stability can be defined in several ways, but the most intuitive definition of a stable system is one having low variability (i.e., little deviation from its average state) despite shifting environmental conditions. This is often termed the resistance of a system. Resilience is a somewhat different aspect of stability indicating the ability of an ecosystem to return to its original state following a disturbance or other perturbation. 物种特性、功能性状和资源利用 物种多样性有两个主要组成部分：物种丰富度（当地群落中的物种数量）和物种组成（群落中物种的身份）。虽然大多数关于生态系统多样性和稳定性之间关系的研究都集中在物种丰富度上，但正是物种组成的变化为解释物种丰富度和生态系统功能之间的关系提供了机制基础。物种在资源利用、环境耐受性以及与其他物种的相互作用方面各不相同，因此物种组成对生态系统的功能和稳定性有重大影响。表征一个物种生态功能的特征被称为功能特征，具有相似特征的物种通常被归类为功能组。当来自不同功能组的物种出现在一起时，它们可以表现出互补的资源利用，这意味着它们在不同的时间使用不同的资源或使用相同的资源。例如，两种动物捕食者可能会消耗不同的猎物，因此它们不太可能相互竞争，从而使系统中捕食者的总生物量更高。就植物而言，所有物种都可能利用相同的资源（空间、光照、水、土壤养分等），但在生长季节的不同时间，例如大草原的早季和晚季草。增加物种多样性可以通过增加物种使用互补资源的可能性来影响生态系统功能，如生产力，也可以增加群落中存在特别多产或高效物种的可能性。例如，高植物多样性可以通过更全面和/或更有效地开发土壤资源（如养分、水）来提高生态系统生产力。虽然初级生产是本文中提及最多的生态系统功能，但分解和养分周转等其他生态系统功能也受到物种多样性和特定物种特征的影响。 Species Identity, Functional traits, and Resource-Use Species diversity has two primary components: species richness (the number of species in a local community) and species composition (the identity of the species present in a community). While most research on the relationship between ecosystem diversity and stability has focused on species richness, it is variation in species composition that provides the mechanistic basis to explain the relationship between species richness and ecosystem functioning. Species differ from one another in their resource use, environmental tolerances, and interactions with other species, such that species composition has a major influence on ecosystem functioning and stability. The traits that characterize the ecological function of a species are termed functional traits, and species that share similar suites of traits are often categorized together into functional groups. When species from different functional groups occur together, they can exhibit complementary resource-use, meaning that they use different resources or use the same resources at different times. For example, two animal predators may consume different prey items, so they are less likely to compete with one another, allowing higher total biomass of predators in the system. In the case of plants, all species may utilize the same suite of resources (space, light, water, soil nutrients, etc.) but at different times during the growing season — for example, early- and late-season grasses in prairies. Increasing species diversity can influence ecosystem functions — such as productivity — by increasing the likelihood that species will use complementary resources and can also increase the likelihood that a particularly productive or efficient species is present in the community. For example, high plant diversity can lead to increased ecosystem productivity by more completely, and/or efficiently, exploiting soil resources (e.g., nutrients, water). While primary production is the ecosystem function most referred to in this article, other ecosystem functions, such as decomposition and nutrient turnover, are also influenced by species diversity and particular species traits. 多样性-稳定性理论 理论模型表明，多样性和稳定性之间可能存在多种关系，这取决于我们如何定义稳定性（Ives&Carpenter评论，2007年）。稳定性可以在生态系统层面上定义——例如，牧场主可能对草原生态系统在几年内维持牛饲料初级生产的能力感兴趣，这些年的平均温度和降水量可能会有所不同。图1显示了如果物种对环境波动的反应各不相同，一个植物群落中存在多个物种可以稳定生态系统过程，从而使一个物种的丰度增加可以补偿另一个物种丰度减少。生物多样性群落也更有可能包含赋予生态系统恢复力的物种，因为随着群落积累物种，其中任何一个物种都有更高的机会拥有能够适应不断变化的环境的特征。这样的物种可以缓冲系统免受其他物种的损失。科学家们提出了保险假说来解释这一现象（Yachi&Loreau，1999年）。在这种情况下，物种身份和特定的物种特征是稳定系统的驱动力，而不是物种丰富度本身。相反，如果稳定性是在物种水平上定义的，那么更多样化的组合实际上可以具有更低的物种水平稳定性。这是因为可以聚集在一个特定群落中的个体数量是有限的，因此随着群落中物种数量的增加，群落中物种的平均种群规模也会下降。例如，在图2中，每个简单的群落只能包含三个个体，因此随着群落中物种数量的增加，任何给定物种拥有大量个体的概率都会下降。一个特定物种的种群规模越小，由于随机波动，它就越有可能在当地灭绝，因此在物种丰富度较高的情况下，当地灭绝的风险应该更大。因此，如果稳定性是从维持群落中特定种群或物种的角度来定义的，那么在随机聚集的群落中增加多样性应该会给系统带来更大的破坏稳定的机会。 Diversity-Stability Theory Theoretical models suggest that there could be multiple relationships between diversity and stability, depending on how we define stability (reviewed by Ives & Carpenter 2007). Stability can be defined at the ecosystem level — for example, a rancher might be interested in the ability of a grassland ecosystem to maintain primary production for cattle forage across several years that may vary in their average temperature and precipitation. Figure 1 shows how having multiple species present in a plant community can stabilize ecosystem processes if species vary in their responses to environmental fluctuations such that an increased abundance of one species can compensate for the decreased abundance of another. Biologically diverse communities are also more likely to contain species that confer resilience to that ecosystem because as a community accumulates species, there is a higher chance of any one of them having traits that enable them to adapt to a changing environment. Such species could buffer the system against the loss of other species. Scientists have proposed the insurance hypothesis to explain this phenomenon (Yachi & Loreau 1999). In this situation, species identity — and particular species traits — are the driving force stabilizing the system rather than species richness per se。In contrast, if stability is defined at the species level, then more diverse assemblages can actually have lower species-level stability. This is because there is a limit to the number of individuals that can be packed into a particular community, such that as the number of species in the community goes up, the average population sizes of the species in the community goes down. For example, in Figure 2, each of the simple communities can only contain three individuals, so as the number of species in the community goes up, the probability of having a large number of individuals of any given species goes down. The smaller the population size of a particular species, the more likely it is to go extinct locally, due to random — stochastic — fluctuations, so at higher species richness levels there should be a greater risk of local extinctions. Thus, if stability is defined in terms of maintaining specific populations or species in a community, then increasing diversity in randomly assembled communities should confer a greater chance of destabilizing the system. 多样性-稳定性关系的实验和观测评估 近年来，人们对多样性、稳定性和生态系统功能之间的关系进行了大量研究（Balvanera等人，2006年，Hooper等人，2005年）。第一个测量多样性和稳定性之间关系的实验操纵了水生微宇宙中的多样性，即包含四个或更多营养级的微型实验生态系统，包括初级生产者、初级和次级消费者以及分解者（McGrady-Steed等人，1997，Naeem和Li，1997）。这些实验发现，物种多样性赋予了几种生态系统功能空间和时间稳定性。功能群内部和功能群之间的物种丰富度赋予了稳定性（Wardle等人，2000年）。当一个系统中有多个物种具有类似的生态作用时，它们有时被认为是“功能冗余的”。但这些实验表明，当单个物种因环境变化（如气候变化）而丧失时，具有功能冗余的物种可能在确保生态系统稳定方面发挥重要作用。最近，科学家们研究了植物多样性对陆地生态系统生态系统稳定性的重要性，尤其是草原，那里的主要植被离地面较低，易于实验操作。1995年，David Tilman及其同事在Cedar Creek生态系统科学保护区建立了168个实验地块，每个地块的大小为9 x 9米（图3A），并从18种可能的多年生植物中随机抽取1、2、4、8或16种进行播种（Tilman等人，2006）。地块被除草以防止新物种入侵，生态系统的稳定性被衡量为初级生产随时间的稳定性。在收集数据的十年里，气候存在显著的年际变化，研究人员发现，随着时间的推移，更多样地的产量更稳定（图3B）。相比之下，在更多样地，种群稳定性下降（图3C）。这些实验结果与上一节中描述的理论一致，预测由于单个物种的种群规模下降，物种多样性的增加将与生态系统水平的稳定性增加呈正相关，而与物种水平的稳定性负相关。操纵多样性的实验因其空间尺度小、时间尺度短而受到批评，那么在较大的空间尺度和较长的时间尺度上，自然聚集的群落会发生什么呢？在一项对内蒙古自然聚集草原植被的24年研究中，Bai等人（2004）观察到物种、功能群和整个群落的生物量随着生长季节降水的强烈年际变化而变化。他们发现，虽然单个物种的丰度波动，但特定功能组内的物种往往会有不同的反应，因此一个物种丰度的下降会被另一个物种的丰度的增加所补偿。这种补偿在波动的环境中稳定了整个社区的生物量生产力（见图1）。这些发现表明，当地物种的丰富性——无论是在功能群内部还是在功能群之间——都赋予了自然聚集群落生态系统过程的稳定性。水生生态系统的实验也表明，大规模过程在稳定生态系统方面发挥着重要作用。加拿大的一项全湖酸化实验发现，尽管物种多样性因酸化而下降，但物种组成发生了显著变化，生态系统功能得以维持（Schindler 1990）。这表明，如果有足够的时间和适当的扩散机制，新物种可以在区域物种库中定居，并补偿那些在当地失去的物种（Fischer等人，2001）。这一观察结果强调了在自然栖息地经历环境变化时保持连通性的重要性。Experiments and Observations Can Evaluate the Diversity-Stability Relationship A wealth of research into the relationships among diversity, stability, and ecosystem functioning has been conducted in recent years (reviewed by Balvanera et al. 2006, Hooper et al. 2005). The first experiments to measure the relationship between diversity and stability manipulated diversity in aquatic microcosms — miniature experimental ecosystems — containing four or more trophic levels, including primary producers, primary and secondary consumers, and decomposers (McGrady-Steed et al. 1997, Naeem & Li 1997). These experiments found that species diversity conferred spatial and temporal stability on several ecosystem functions. Stability was conferred by species richness, both within and among functional groups (Wardle et al. 2000). When there is more than one species with a similar ecological role in a system, they are sometimes considered 'functionally redundant.' But these experiments show that having functionally redundant species may play an important role in ensuring ecosystem stability when individual species are lost due to environmental changes, such as climate change. More recently, scientists have examined the importance of plant diversity for ecosystem stability in terrestrial ecosystems, especially grasslands where the dominant vegetation lies low to the ground and is easy to manipulate experimentally. In 1995, David Tilman and colleagues established 168 experimental plots in the Cedar Creek Ecosystem Science Reserve, each 9 x 9 m in size (Figure 3A), and seeded them with 1, 2, 4, 8 or 16 species drawn randomly from a pool of 18 possible perennial plant species (Tilman et al. 2006). Plots were weeded to prevent new species invasion and ecosystem stability was measured as the stability of primary production over time. Over the ten years that data were collected, there was significant interannual variation in climate, and the researchers found that more diverse plots had more stable production over time (Figure 3B). In contrast, population stability declined in more diverse plots (Figure 3C). These experimental findings are consistent with the theory described in the prior section, predicting that increasing species diversity would be positively correlated with increasing stability at the ecosystem-level and negatively correlated with species-level stability due to declining population sizes of individual species. Experiments manipulating diversity have been criticized because of their small spatial and short time scales, so what happens in naturally assembled communities at larger spatial scales over longer time scales? In a 24-year study of naturally assembled Inner Mongolia grassland vegetation, Bai et al. (2004) observed variation in the biomass of species, functional groups, and the whole community in response to strong interannual variation in growing-season precipitation. They found that while the abundance of individual species fluctuated, species within particular functional groups tended to respond differently such that a decrease in the abundance of one species was compensated for by an increase in the abundance of another. This compensation stabilized the biomass productivity of the whole community in a fluctuating environment (see Figure 1). These findings demonstrate that local species richness — both within and among functional groups — confers stability on ecosystem processes in naturally assembled communities. Experiments in aquatic ecosystems have also shown that large-scale processes play a significant role in stabilizing ecosystems. A whole-lake acidification experiment in Canada found that although species diversity declined as a result of acidification, species composition changed significantly and ecosystem function was maintained (Schindler 1990). This suggests that given sufficient time and appropriate dispersal mechanisms, new species can colonize communities from the regional species pool and compensate for those species that are locally lost (Fischer et al. 2001). This observation emphasizes the importance of maintaining connectivity among natural habitats as they experience environmental changes. |
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