How does global land-use change reshape ecological assemblages over time?

由于人类活动的影响，全球陆地生物多样性正在减少，其中土地利用的变化迄今是最重要的。当人们改变土地的使用方式时，许多原本存在的物种从该地区衰落或消失，而其他以前没有的物种则得到了确立。尽管一些物种立即受到影响，但其他物种可能只会在土地利用变化的后果波及整个生态系统时才会做出反应。到目前为止，这种延迟或延长的反应，我们称之为“生物滞后”，在大规模模型中基本上被忽视了。以前的许多工作的另一个缺点是，它关注的是物种的数量，而不是它们做了什么。因为这种变化的“赢家”很可能与“输家”在生态上不同，土地利用的变化会影响群落的功能，以及它包含了多少物种。了解土地利用变化如何以及以多快的速度影响当地群落，对于在未来几十年支持更好的土地利用决策至关重要，因为人们试图在对生态系统产品的短期需求和对可持续发展的长期需求之间取得平衡。评估土地利用变化对当地生态社区的全球影响的最明显方法是监测几十年来一大批具有代表性的地点的土地利用和社区如何变化。这些网站必须具有代表性，以避免有偏见的结果，而且需要较长的时间范围，因为回应可能会在多年后展开。因为没有这样一套网站，所以需要不那么直接的方法。我们正计划搜索生态文献，比较土地利用变化前后的群落。我们可以纠正偏见，因为我们对土地利用的不同变化有多普遍进行了估计；我们将对土地利用变化后的反应随时间变化进行建模，以便我们可以使用长期和短期研究。有数百项合适的研究，我们将要求制作这些研究的研究人员与我们分享他们的数据；然后我们将在项目结束时将这些数据提供给所有人。我们将把土地利用变化前后物种丰富度的数据与它们的生态作用的信息结合起来，揭示土地利用变化如何以及如何迅速地影响各种物种的相对丰富度以及群落的生态结构和功能。例如，自然栖息地向农业的转变是否倾向于偏爱较小的物种而不是较大的物种，如果是的话，速度会有多快？在更多人类主导的土地利用中，新陈代谢会更快吗？这些分析将需要对几个具有重要生态意义和高度多样化的节肢动物群体的特征数据进行新的汇编；为了产生这些数据，我们将利用自然历史博物馆的专业知识、藏品和图书馆。在NERC早期资助的一个项目(预测：www.forects.org.uk)中，我们已经汇编了500多个数据集--由300多名不同的研究人员提供--比较了不同土地利用的匹配地点。Predicts数据库已经从88个国家的18,000多个站点积累了200多万条记录。该数据库包含的物种数量是正式描述的1%以上。我们对这一史无前例的庞大和具有代表性的数据集的分析表明，土地利用的变化对全球平均地方多样性产生了显著影响。然而，由于预测的数据集是空间而不是时间的比较，它们不太适合分析组合如何对土地利用变化做出反应的动态。更根本的是，预测的假设，即空间比较是时间数据的适当替代品，现在需要检验。这项提案将提供必要的测试，并提供土地利用变化如何随着时间的推移重塑生态组合的最全面的图景。

Terrestrial biodiversity is declining globally because of human impacts, of which land-use change has so far been the most important. When people change how land is used, many of the species originally present decline or disappear from the area, while others previously absent become established. Although some species are affected immediately, others might only respond later as the consequences of the land-use change ripple through the ecosystem. Such delayed or protracted responses, which we term 'biotic lag', have largely been ignored in large-scale models so far. Another shortcoming of much previous work is that it has focused on numbers of species, rather than what they do. Because 'winners' from the change are likely to be ecologically different from 'losers', the land-use change impacts how the assemblage functions, as well as how many species it contains. Understanding how - and how quickly - land-use change affects local assemblages is crucial for supporting better land-use decisions in the decades to come, as people try to strike the balance between short-term needs for products from ecosystems and the longer-term need for sustainability.The most obvious way to assess the global effects of land-use change on local ecological communities would be to have monitored how land use and the community have changed over a large, representative set of sites over many decades. The sites have to be representative to avoid a biased result, and the long time scale is needed because the responses can unfold over many years. Because there is no such set of sites, less direct approaches are needed. We are planning to scour the ecological literature for comparisons of communities before and after land-use change. We can correct for bias because we have estimates of how common different changes in land use have been; and we will model how responses change over time after a land-use change so that we can use longer-term and shorter-term studies alike. There are many hundreds of suitable studies, and we will ask the researchers who produced them to share their data with us; we will then make them available to everyone at the end of the project.We will combine data on species' abundances before and after the land-use change with information about their ecological roles, to reveal how - and how quickly - changing land use affects the relative abundances of the various species and the ecological structure and function of the community. Does conversion of natural habitats to agriculture tend to favour smaller species over large ones, for instance, and if so how quickly? Is metabolism faster in more human-dominated land uses? These analyses will require new compilations of trait data for several ecologically important and highly diverse arthropod groups; to produce these, we will make use of the expertise, collections and library of the Natural History Museum.In an earlier NERC-funded project (PREDICTS: www.predicts.org.uk), we have already compiled over 500 data sets - provided by over 300 different researchers - that compared otherwise-matched sites where land use differed. The PREDICTS database has amassed over 2,000,000 records, from over 18,000 sites in 88 countries. The database contains more than 1% as many species as have been formally described. Our analyses of this unprecedentedly large and representative data set indicates that land-use change has had a marked global impact on average local diversity. However, because PREDICTS' data sets are spatial rather than temporal comparisons, they are not well-suited to analysing the dynamics of how assemblages respond to land-use change. More fundamentally, PREDICTS' assumption that spatial comparisons are an adequate substitute for temporal data now needs testing. This proposal will deliver the necessary tests, as well as producing the most comprehensive picture of how land-use change reshapes ecological assemblages through time.