Direct and indirect effects of invasive species: biodiversity loss is a major mechanism by which an invasive tree affects ecosystem functioning

1.Global change, such as exotic invasions, dramatically affects ecosystem functioning. However, the mechanisms behind the impacts are often unclear and despite extensive experimental work, we know little about the importance of biodiversity loss as a component of global change effects in real‐world ecosystems. 2.We disentangled several mechanisms by which an exotic invader affected ecosystem functioning in East African drylands in Kenya and Ethiopia. We used structural equation modelling to separate direct effects of a woody invader (Prosopis juliflora) on a range of ecosystem functions from indirect effects mediated through changes in biodiversity (plant species richness) and ecosystem functioning (herbaceous biomass). We analysed effects on ecosystem functions linked to soil biogeochemical cycling and transfer of energy between trophic levels. 3.We found that the mean size of individual indirect effects mediated by biodiversity and herbaceous biomass was about twice as large as ...1. 全球变化（Global change），如外来物种入侵，会显著影响生态系统功能（ecosystem functioning）。然而，其背后的影响机制往往尚不明确；尽管已开展大量实验研究，我们对生物多样性丧失作为全球变化效应的组成部分在真实世界生态系统中的重要性仍知之甚少。 2. 本研究解析了肯尼亚与埃塞俄比亚境内东非旱地中，外来入侵物种影响生态系统功能的多种作用机制。我们采用结构方程模型（Structural Equation Modelling），将木本入侵物种——牧豆树（Prosopis juliflora）对一系列生态系统功能的直接效应，与通过生物多样性（植物物种丰富度）及生态系统功能（草本生物量）变化介导的间接效应分离开来。此外，我们还分析了该入侵物种对与土壤生物地球化学循环（soil biogeochemical cycling）及营养级间能量传递相关的生态系统功能的影响。 3. 我们发现，由生物多样性与草本生物量介导的单个间接效应的平均强度约为……