Livestock activity increases exotic plant richness, but wildlife increases native richness, with stronger effects under low productivity

1.Grazing by domestic livestock is one of the most widespread land uses worldwide, particularly in rangelands, where it co-occurs with grazing by wild herbivores. Grazing effects on plant diversity are likely to depend on intensity of grazing, herbivore type, coevolution with plants and prevailing environmental conditions. 2.We collected data on climate, plant productivity, soil properties, grazing intensity and herbivore type; and measured their effects on plant species richness from 451 sites across 0.4 M km2 of semi-arid rangelands in eastern Australia. We used structural equation modelling to examine the direct and indirect effects of increasing grazing intensity by different herbivores (cattle, sheep, kangaroos, rabbits) on native and exotic plant species richness across all sites, and in subsets focusing on three woodland communities spanning a gradient in productivity. 3.Direct effects of grazing by all herbivores were strongest under low productivity but waned with increas...1. 家畜放牧是全球分布最为广泛的土地利用方式之一，尤其在牧场（rangelands）中，该区域常与野生草食动物的放牧活动共存。放牧对植物多样性的影响，大概率取决于放牧强度、草食动物种类、与植物的协同进化关系以及当前的环境条件。 2. 本研究收集了气候、植物生产力、土壤属性、放牧强度以及草食动物种类相关数据，并基于澳大利亚东部0.4百万平方公里半干旱牧场（semi-arid rangelands）内的451个样地，分析了各因素对植物物种丰富度的影响。本研究采用结构方程模型（structural equation modelling），探究了不同草食动物（牛、绵羊、袋鼠、野兔）的放牧强度提升，对全部样地以及以三个沿生产力梯度分布的林地群落（woodland communities）为研究对象的子集内的本土与外来植物物种丰富度的直接与间接影响。 3. 所有草食动物的放牧直接效应在低生产力条件下最为显著，但随...逐渐减弱