The theory of “top-down” ecological regulation predicts that herbivory suppresses plant abundance, biomass, and survival but increases diversity through the disproportionate consumption of dominant species, which inhibits competitive exclusion. To date, these outcomes have been clear in aquatic ecosystems but not on land. We explicate this discrepancy using a meta-analysis of experimental results from 123 native animal exclusions in natural terrestrial ecosystems (623 pairwise comparisons). Consistent with top-down predictions, we found that herbivores significantly reduced plant abundance, biomass, survival, and reproduction (all P < 0.01) and increased species evenness but not richness (P = 0.06 and P = 0.59, respectively). However, when examining patterns in the strength of top-down effects, with few exceptions, we were unable to detect significantly different effect sizes among biomes, based on local site characteristics (climate or productivity) or study characteristics (study duration or exclosure size). The positive effects on diversity were only significant in studies excluding large animals or located in temperate grasslands. The results demonstrate that top-down regulation by herbivores is a pervasive process shaping terrestrial plant communities at the global scale, but its strength is highly site specific and not predicted by basic site conditions. We suggest that including herbivore densities as a covariate in future exclosure studies will facilitate the discovery of unresolved macroecology trends in the strength of herbivore–plant interactions.

“自上而下”的生态调节理论预测，食草会抑制植物的丰度，生物量和生存，但会通过不均衡地消耗优势物种来增加多样性，从而抑制竞争排斥。迄今为止，这些结果在水生生态系统中很明显，但在陆地上尚不明确。我们通过对来自天然陆生生态系统中123种自然动物的实验结果进行荟萃分析，阐明了这种差异（623个成对比较）。与自上而下的预测一致，我们发现食草动物显着降低了植物的丰度，生物量，存活率和繁殖力（所有P <0.01），并增加了物种的均匀度，但没有增加丰富度（P = 0.06和P分别为0.59）。但是，在检查自上而下效果的强度模式时，除少数例外，我们无法根据当地的地点特征（气候或生产力）或研究特征（研究持续时间或排除规模）来检测生物群落之间显着不同的效应大小。 。对多样性的积极影响仅在排除大型动物或在温带草原的研究中才有意义。结果表明，草食动物自上而下的调控是一个遍及全球的陆地植物群落的普遍形成过程，但其强度具有高度的地点特异性，而不受基本地点条件的预测。