Distribution and impact of the Argentine ant, Linepithema humile (Mayr), in South Africa

Invasion by the notorious tramp species, the Argentine ant (Linepithema humile Mayr) (Hymenoptera: Formicidae) has caused major concern around the globe, owing to its displacement of native ant species and other invertebrates where it invades. This species was first recorded in South Africa in 1901 in Stellenbosch, Western Cape Province (WCP), and has now become a significant pest in most urban and agricultural areas in the country. The Argentine ant has received relatively little attention in South Africa compared to other countries (e.g. California, North America). To date the extent of invasion by this species countrywide, as well as its impact on the local ant fauna inside protected areas, has not been quantified. In this study, the impact of the Argentine ant on native ant fauna inside three protected areas in the WCP (Helderberg Nature Reserve (HNR), Jonkershoek Nature Reserve (JNR) and Kogelberg Biosphere Reserve KBR)) was assessed. Species richness and diversity were compared between invaded and uninvaded bait stations at each protected area. Several native ant species were found to be displaced by the Argentine ant from all three protected areas, although three species: Meranoplus peringueyi, Monomorium sp. 8 and Tetramorium quadrispinosum, were found coexisting with it. Invaded bait stations had significantly lower ant species richness and species turnover than uninvaded bait stations. Uninvaded bait stations contained eight times more native ant species than invaded bait stations. Thus, the invasion of protected areas by the Argentine ant has severe negative consequences for the species richness and assemblage structure of native ants, leading to the biotic homogenization of these local ant communities. The distribution range of the Argentine ant inside the three protected areas (HNR, JNR, KBR), as well as microhabitat preferences that may facilitate the spread of this species inside these reserves, was also assessed. Helderberg Nature Reserve was the most invaded protected area, with the highest level of the Argentine ant occupancy, while JNR and KBR had lower occupancy levels. At all the three protected areas, this species was dominant at lower altitudinal areas, and also showed a clear preference for areas with high anthropogenic disturbances, i.e. around buildings and on lawns (picnic areas). In this study, there was no evidence that moisture availability facilitates the distribution and spread of the Argentine ant inside these reserves. Finally, a combination of published literature records, museum records and records collected in the current study was used to quantify the current distributional extent of the Argentine ant throughout urban South Africa. This is the first study quantifying the distribution and extent of invasion by the Argentine ant throughout the country. The Argentine ant was found in six of the nine South African Provinces, and its extent of occurrence includes approximately half of the country's land surface area. Discontinuities in the distribution of the Argentine ant across the country revealed that range expansion of the Argentine ant in South Africa is occurring predominantly via human-mediated jump dispersal, rather than naturally via nest diffusion. This study clearly demonstrated that the Argentine ant is well established across South Africa as well as inside protected areas. The Argentine ant invasion was influenced by the presence of human modified landscapes (i.e. buildings) both at low and high altitude, and this was associated with higher rates of native ant species displacement at these areas. Therefore, limiting the development of recreational areas, such as buildings and picnic sites inside protected areas will result in the lower rate of spread of the Argentine ant. This will in turn lower the extent of displacement of native ant species.To determine the distribution and impact of the Argentine ant in South Africa.

臭名昭著的流浪物种——阿根廷蚂蚁（Linepithema humile Mayr）（膜翅目：蚁科）在全球范围内引发了广泛关注，因其入侵并取代了原生的蚂蚁物种和其他无脊椎动物。该物种首次于1901年在南非开普省（Western Cape Province，WCP）的斯泰伦博斯被记录，如今已成为该国城市和农业区域的主要害虫。相较于其他国家（如北美的加利福尼亚州），阿根廷蚂蚁在南非所受到的关注相对较少。截至目前，该物种在南非全境的入侵范围及其对保护区内本地蚂蚁群落的影响尚未得到量化。在本研究中，评估了阿根廷蚂蚁对WCP内三个保护区（Helderberg自然保护区（HNR）、Jonkershoek自然保护区（JNR）和Kogelberg生物圈保护区（KBR））内本地蚂蚁群落的影响。在每个保护区内，被入侵和未被入侵的诱捕站之间的物种丰富度和多样性进行了比较。发现几个本地蚂蚁物种被阿根廷蚂蚁从三个保护区中驱逐出去，尽管三种物种：Meranoplus peringueyi、Monomorium sp. 8和Tetramorium quadrispinosum，与它共存。被入侵的诱捕站的蚂蚁物种丰富度和物种周转率显著低于未被入侵的诱捕站。未被入侵的诱捕站包含的本地蚂蚁物种数量是被入侵诱捕站的八倍。因此，阿根廷蚂蚁对保护区的入侵严重影响了本地蚂蚁物种的丰富度和群落结构，导致这些本地蚂蚁群落生物多样性的同质化。此外，还评估了阿根廷蚂蚁在三个保护区（HNR、JNR、KBR）内的分布范围以及可能促进该物种在这些保护区内部传播的微生境偏好。Helderberg自然保护区是最被入侵的保护区，阿根廷蚂蚁的占据水平最高，而JNR和KBR的占据水平较低。在所有三个保护区内，该物种在低海拔地区占主导地位，并且对人类活动强烈干扰的区域，如建筑物和草坪（野餐区）表现出明显的偏好。在本研究中，没有证据表明水分的可用性促进了阿根廷蚂蚁在这些保护区内的分布和传播。最后，结合已发表的文献记录、博物馆记录和本研究收集的记录，量化了阿根廷蚂蚁在南非城市中的当前分布范围。这是首次量化阿根廷蚂蚁在整个国家分布和入侵范围的研究。研究发现，阿根廷蚂蚁在南非九个省中的六个省被发现，其分布范围约占国家陆地面积的半数。阿根廷蚂蚁在南非国内的分布不连续性揭示了该物种在南非的扩张主要是通过人为介导的跳跃扩散，而不是通过自然巢穴扩散。本研究明确证明了阿根廷蚂蚁在南非以及保护区内的广泛定殖。阿根廷蚂蚁的入侵受到人类改造景观（即建筑物）在低海拔和高海拔地区的存在的影响，这与这些地区本地蚂蚁物种被驱逐的速度加快相关。因此，限制保护区内部娱乐区（如建筑物和野餐区）的发展将降低阿根廷蚂蚁的传播速度。这将进而降低本地蚂蚁物种被驱逐的范围。为了确定阿根廷蚂蚁在南非的分布和影响。