Increases in the cover or density of woody plants (encroachment) and overgrazing by European livestock are 2 major drivers of ecosystem structure and function in drylands and are often associated with land degradation. Although the effects of encroachment and overgrazing on vascular plants are relatively well known, little is known about their effects on arthropods such as ants. We examined ant community composition at sites ranging in shrub cover in a wooded dryland in eastern Australia, testing the notion that increasing shrub cover and grazing intensity would alter ant assemblages and functional group composition. We used ants because they are abundant, diverse, and respond to small-scale environmental changes. Increasing shrub cover had no effect on ant richness, diversity, or evenness but increased the abundance of Subordinate Camponotini. Larger shrubs tended to have greater ant richness, and abundance of Cold Climate Specialists, but fewer Generalized Myrmicinae and Hot Climate Specialists. More intense grazing was associated with greater ant richness, diversity, and evenness; a greater abundance of Hot Climate Specialists and Dominant Dolichoridae; and lower abundance of Subordinate Camponotini. Our study indicates that changes in grazing intensity had stronger effects on ant richness than any increase in shrub cover. The effects of grazing likely resulted from changes in soil surface complexity such as barer ground associated with grazing-induced degradation.

中文翻译：

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蚂蚁对放牧的反应比灌木覆盖的变化更强烈

木本植物覆盖率或密度的增加（侵占）和欧洲牲畜的过度放牧是旱地生态系统结构和功能的两个主要驱动因素，并且通常与土地退化有关。尽管侵占和过度放牧对维管植物的影响相对众所周知，但对它们对节肢动物（如蚂蚁）的影响知之甚少。我们检查了澳大利亚东部树木繁茂的旱地灌木覆盖范围内的蚂蚁群落组成，测试了增加灌木覆盖和放牧强度会改变蚂蚁组合和功能群组成的概念。我们使用蚂蚁是因为它们数量众多、种类繁多，并且能够对小规模的环境变化做出反应。增加灌木覆盖对蚂蚁的丰富度、多样性或均匀度没有影响，但增加了下属 Camponotini 的丰度。较大的灌木往往有更丰富的蚂蚁和丰富的寒冷气候专家，但较少的广义 Myrmicinae 和炎热气候专家。更强烈的放牧与更大的蚂蚁丰富度、多样性和均匀度有关；更丰富的热气候专家和优势 Dolichoridae；和较低丰度的下属 Camponotini。我们的研究表明，放牧强度的变化对蚂蚁丰富度的影响比灌木覆盖率的任何增加都要大。放牧的影响可能源于土壤表面复杂性的变化，例如与放牧引起的退化相关的裸露地面。多样性和均匀性；更丰富的热气候专家和优势 Dolichoridae；和较低丰度的下属 Camponotini。我们的研究表明，放牧强度的变化对蚂蚁丰富度的影响比灌木覆盖率的任何增加都要大。放牧的影响可能源于土壤表面复杂性的变化，例如与放牧引起的退化相关的裸露地面。多样性和均匀性；更丰富的热气候专家和优势 Dolichoridae；和较低丰度的下属 Camponotini。我们的研究表明，放牧强度的变化对蚂蚁丰富度的影响比灌木覆盖率的任何增加都要大。放牧的影响可能源于土壤表面复杂性的变化，例如与放牧引起的退化相关的裸露地面。