Data from: Herbivores safeguard plant diversity by reducing variability in dominance

1. Reductions in community evenness can lead to local extinctions as dominant species exclude subordinate species; however, herbivores can prevent competitive exclusion by consuming otherwise dominant plant species, thus increasing evenness. While these predictions logically result from chronic, gradual reductions in evenness, rapid, temporary pulses of dominance may also reduce species richness. Short pulses of dominance can occur as biotic or abiotic conditions temporarily favor one or a few species, manifested as increased temporal variability (the inverse of temporal stability) in community evenness. Here, we tested whether consumers help maintain plant diversity by reducing the temporal variability in community evenness. 2. We tested our hypothesis by reducing herbivore abundance in a detailed study of a developing, tallgrass prairie restoration. To assess the broader implications of the importance of herbivory on community evenness as well as potential mechanisms, we paired this study with a global herbivore-reduction experiment. 3. We found that herbivores maintained plant richness in a tallgrass prairie restoration by limiting temporary pulses in dominance by a single species. Dominance by an annual species in a single year was negatively associated with species richness, suggesting that short pulses of dominance may be sufficient to exclude subordinate species. 4. The generality of this site-level relationship was supported by the global experiment in which inter-annual variability in evenness declined in the presence of vertebrate herbivores over timeframes ranging in length from 2-5 years, preventing declines in species richness. Furthermore, inter-annual variability of community evenness was also negatively associated with pre-treatment species richness. 5. Synthesis: A loss or reduction of herbivores can destabilize plant communities by allowing brief periods of dominance by one or a few species, potentially triggering a feedback cycle of dominance and extinction. Such cycles may not occur immediately following the loss of herbivores, being delayed until conditions allow temporary periods of dominance by a subset of plant species.1. 群落均匀度（community evenness）下降可引发局部灭绝，此过程中优势种会排除从属种；而草食动物（herbivores）可取食原本占据优势的植物物种，从而阻断竞争排除（competitive exclusion），提升群落均匀度。尽管上述推论源于群落均匀度的长期、渐进式下降，但快速且短暂的优势脉冲同样可能降低物种丰富度（species richness）。当生物或非生物条件短期偏向某一个或少数几个物种时，便会出现短暂的优势脉冲，表现为群落均匀度的时间变异性（temporal variability，即时间稳定性的反面）升高。本研究旨在验证：消费者是否可通过降低群落均匀度的时间变异性，维持植物多样性。 2. 我们在一项针对正在恢复中的高草草原（tallgrass prairie）的详细研究中，通过降低草食动物种群数量来验证上述假说。为评估草食作用对群落均匀度的重要性及其潜在机制的广泛意义，我们将该本地研究与一项全球范围的草食动物去除实验相结合。 3. 我们在高草草原恢复样地中发现，草食动物通过限制单一物种出现短暂优势脉冲，维持了植物物种丰富度。某一年生植物在单一年份占据优势的现象，与物种丰富度呈负相关，这表明短暂的优势脉冲足以排除从属种。 4. 全球实验验证了该样地水平关系的普遍性：在2至5年的观测周期内，有脊椎动物草食动物存在时，群落均匀度的年际变异性会下降，从而阻止了物种丰富度的降低。此外，群落均匀度的年际变异性还与处理前的物种丰富度呈负相关。 5. 综合分析：草食动物的缺失或种群减少，会让某一个或少数几个物种获得短暂的优势地位，从而破坏植物群落的稳定性，甚至可能引发优势化-灭绝的反馈循环。这类循环不会在草食动物消失后立刻出现，而是会延迟至环境条件允许部分植物物种出现短暂优势状态时才会发生。