1. Human‐caused loss of vertebrate and invertebrate animals, defaunation, is increasing, and potentially affects plant community structure of diverse grassland ecosystems world‐wide.
2. We experimentally simulated defaunation using size‐selective fences to progressively exclude large‐, medium‐ and small‐sized mammals, and invertebrates from two subalpine vegetation types in the Swiss National Park (SNP): intensively grazed short‐grass and moderately grazed tall‐grass vegetation. We assessed plant community properties yearly from 2009 to 2013, and examined treatment effects on plant community structure in the two grassland types.
3. In the short‐grass vegetation, the exclusion of large mammals increased total plant biomass, while the exclusion of large and medium‐sized mammals increased total, grass and forb biomass compared to when all animals had access. These increases became stronger when invertebrates were also excluded. The exclusion of all mammals and invertebrates increased biomass of grasses by 205%, forbs by 100% and total plant biomass by 118% compared to when all animals had access, hence enhancing relative biomass of grasses from 43.6% to 60%, changing plant species composition and lowering richness of forbs by 16%, the number of plant families by 13% and family‐level Shannon diversity by 23%. In contrast to these significant community‐level responses found in the short‐grass vegetation, there was no evidence that the size‐selective exclusion of animals altered the plant community structure of the tall‐grass vegetation. The contrasting results were due to the difference in plant community composition prior to our experiment, which were related to differences in quantity and quality of forage and in grazing intensities of herbivores between the two grassland types.
4. Synthesis. Our results showed that different‐sized animals, in particular large mammals and invertebrates, contributed to maintain the plant community structure in the short‐grass vegetation, highlighting the importance of multiple, functionally different animal groups for ecosystem functioning and stability. In contrast to the short‐grass vegetation, we could not detect such a top‐down control by animals in the tall‐grass vegetation. Our results suggest that potential defaunation effects on grassland plant community structure depend on the degree of grazing pressure release and grassland vegetation type.

中文翻译：

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根据植被类型的不同，对哺乳动物和无脊椎动物的大小选择性排斥对草原植物群落的影响不同

1. 人为造成的脊椎动物和无脊椎动物的丧失，毁灭性现象正在增加，并有可能影响世界范围内各种草地生态系统的植物群落结构。
2. 我们使用尺寸选择性栅栏对去皮进行了实验模拟，以逐步排除大，中，小型哺乳动物以及瑞士国家公园（SNP）中两种亚高山植被类型的无脊椎动物：密集放牧的短草和中等放牧的高草植被。我们从2009年至2013年每年评估植物群落特性，并研究了两种草地类型对植物群落结构的处理效果。
3. 与所有动物均可进入的情况相比，在短草植被中，大型哺乳动物的排除增加了植物总生物量，而大型和中型哺乳动物的排除增加了总生物量，草和Forb生物量。当无脊椎动物也被排除在外时，这些增加变得更强。与所有动物均可进入的情况相比，排除所有哺乳动物和无脊椎动物，草的生物量增加了205％，草类减少了100％，植物总生物量增加了118％，因此草的相对生物量从43.6％增加到60％，改变了植物种类的组成和降低的福布斯丰富度16％，植物科数量减少13％，家庭一级的香农多样性降低23％。与在短草植被中发现的这些重要的社区级反应相反，没有证据表明对动物的大小选择性排斥改变了高草植被的植物群落结构。对比结果是由于我们的实验之前植物群落组成的差异，这与两种草原类型之间草料的数量和质量以及草食动物的放牧强度的差异有关。
4. 综合。我们的结果表明，不同大小的动物，特别是大型哺乳动物和无脊椎动物，有助于维持短草植被中的植物群落结构，突出了多种功能上不同的动物对生态系统功能和稳定性的重要性。与短草植被相反，我们无法检测到高草植被中动物对这种自上而下的控制。我们的结果表明，对草地植物群落结构的潜在破坏作用取决于放牧压力释放的程度和草地植被类型。