Investigating the impact of pompom weed (Campuloclinium macrocephalum) on invertebrate diversity in the grasslands of Gauteng.

In South Africa, the grassland biome is being invaded by a South American herb, commonly known as pompom weed (Campuloclinium macrocephalum). Changes in the natural grassland vegetation are likely to affect the native invertebrate assemblages, but to date it remains unknown how pompom weed affects invertebrate diversity. To quantify this effect, we compared Coleoptera (beetle) and Cicadellidae (leafhopper) assemblages between uninvaded and invaded treatments, as well as the beetle assemblage seperately, divided into canopy-dwelling and ground-dwelling beetles, using unbaited pitfall traps and sweepnet sampling. Specimens were identified to species level and it was shown that the beetle assemblage had a higher species richness in uninvaded sites, but an elevated abundance of certain species in the invaded sites. In contrast, the leafhopper assemblage had a higher species richness in the invaded sites and a four times higher abundance in the uninvaded sites. Ground-dwelling beetles did not show any difference in species richness or abundance between treatments, but canopy-dwelling beetles once again had a higher richness in uninvaded sites and an inflated abundance in the invaded sites. Ordinations showed that invertebrate assemblage compositions asssociated with each treatment were different for all the assemblages studied except the ground-dwelling beetles. Although pompom weed appears to be an attractive resource habitat for certain native invertebrates, some species might be lost if grassland habitats continue to be invaded by pompom weed.在南非，草原生物群系（grassland biome）正遭受一种南美草本植物入侵，该植物俗称绒球草（pompom weed，Campuloclinium macrocephalum）。天然草原植被的变化大概率会影响本土无脊椎动物群落（invertebrate assemblages），但截至目前，绒球草对无脊椎动物多样性的具体影响仍未明确。为量化该入侵的生态影响，我们采用无诱饵陷阱法（unbaited pitfall traps）与扫网采样法（sweepnet sampling），对比了未入侵与入侵样地中的鞘翅目（Coleoptera，甲虫）和叶蝉科（Cicadellidae，叶蝉）群落；同时单独针对甲虫群落，按树冠栖居甲虫与地面栖居甲虫两类开展细分分析。所有标本均鉴定至物种水平，结果显示：未入侵样地的甲虫群落物种丰富度（species richness）更高，但入侵样地中部分物种的个体丰度（abundance）有所提升。与之相反，入侵样地的叶蝉群落物种丰富度更高，而未入侵样地的叶蝉个体丰度则为入侵样地的四倍。地面栖居甲虫的物种丰富度与个体丰度在两类样地间均无显著差异，但树冠栖居甲虫再次呈现出未入侵样地物种丰富度更高、入侵样地个体丰度偏高的特征。多元排序分析（ordinations）结果表明，除地面栖居甲虫外，其余所有研究的无脊椎动物群落组成在两类样地间均存在显著差异。尽管绒球草似乎可为部分本土无脊椎动物提供适宜的栖息资源，但如果草原生境持续遭受绒球草入侵，部分物种可能会因此丧失。