Biodiversity-ecosystem functioning relationships in freshwaters: a food web perspective

生态系统过程和群落结构有着千丝万缕的联系，正如近年来越来越多地描述的（通常是积极的）“生物多样性-生态系统功能”（B-EF）关系所揭示的那样。由于与人类活动相关的环境压力因素正在造成整个欧洲生物多样性的显著下降，这可能会破坏自然系统的正常功能。然而，目前，人们对淡水中生物多样性丧失对生态系统过程的潜在影响，以及最终对具有社会经济价值的“商品和服务”（例如，清洁水的供应；休闲渔业）的供应的潜在影响知之甚少。由于大多数B-EF实验仅限于陆地草原的单一营养级系统，因此它们缺乏普遍性，这进一步加剧了这种知识的缺乏。多营养系统（即大多数真实的生态系统）的行为可能非常不同：在淡水中尤其如此，在淡水中，捕食者-猎物的相互作用可能对生态系统过程产生深远的影响。此外，物种“特征”的多样性可能比分类多样性本身更重要，特别是在物种营养相似的系统中，许多淡水食物网似乎都是如此。事实上，溪流系统中的B-EF曲线通常在物种丰富度较低时达到饱和（通常为3个物种）。许多B-EF实验的另一个重要缺点是，它们的组合是通过从物种池中随机抽样构建的，而物种损失是高度非随机的：大的、罕见的和/或在食物网中处于高位的分类群往往是第一个失去的。拟议的研究旨在解决以前B-EF研究的这些缺点，特别侧重于应用更现实的食物网视角。具体来说，我们将研究非随机物种损失如何影响多个生态系统过程（分解、初级生产、草食），这些过程决定了向更高营养水平的能量通量，这些水平通常具有高社会经济价值（例如鲑科鱼类）。重点实验室试验将与实地调查和操作相结合，探索多营养系统中B-EF关系背后的机制，重点是性状（而不是简单的分类）多样性。我们将从两个方向解决这些问题：1)博士后研究助理将通过实验探索生物多样性变化对生态系统功能的影响；2)绑博士研究生将通过结合调查、实验和数学模型，专门关注气候变化的潜在影响，气候变化已被确定为未来一个世纪淡水的主要压力源。

Ecosystem processes and community structure are inextricably linked, as revealed by the (usually positive) 'biodiversity-ecosystem functioning' (B-EF) relationships that have been described increasingly in recent years. Because environmental stressors associated with human activity are causing significant declines in biodiversity across Europe, this threatens to disrupt the normal functioning of natural systems. At present, however, the potential impacts of biodiversity loss on ecosystem processes and, ultimately, on the supply of 'goods and services' of socioeconomic value (e.g. the supply of clean water; recreational fisheries) are poorly understood in freshwaters. This lack of knowledge is further compounded by the fact that most B-EF experiments have been restricted to single trophic level systems in terrestrial grasslands, and as such they lack generality. Multi-trophic systems (i.e. most real ecosystems) can behave very differently: this is particularly true in freshwaters, where predator-prey interactions can have profound effects on ecosystem processes. Further, the diversity of species 'traits' may be more important than taxonomic diversity per se, especially in systems where species are trophically similar, as appears to be true of many freshwater food webs. Indeed, B-EF curves in stream systems often reach saturation at low levels of species richness (typically about 3 species per guild). A further important shortcoming of many B-EF experiments is that they have assemblages that have been constructed by random sampling from a species pool, whereas species-loss is highly non-random: taxa that are big, rare and/or high in the food web are often the first to be lost. The proposed research has been designed to address these shortcomings of previous B-EF research, with a particular focus on applying a more realistic food web perspective. Specifically, we will investigate how non-random species loss affects multiple ecosystem processes (decomposition, primary production, herbivory) that determine the flux of energy to the higher trophic levels, which are often of high socioeconomic value (e.g. salmonid fishes). Focussed laboratory trials will be combined with field surveys and manipulations to explore mechanisms behind B-EF relationships in multitrophic systems, with an emphasis on trait (as opposed to simply taxonomic) diversity. We will approach these questions from two directions: 1) a Postdoctoral Research Assistant will explore, experimentally, the consequences of biodiversity change for ecosystem functioning and 2) a Tied PhD student will focus specifically on the potential impacts of climate change, which has been identified as a major stressor for freshwaters over the coming century, by using a combination of surveys, experiments and mathematical modelling.