Chapter 2 Raw Data

Plant invasions likely impact entire arthropod communities but most research focuses either on insect controls or select target plant species. In Western Montana, USA, vegetation and arthropod communities were compared between intermountain grassland habitats uninvaded by spotted knapweed (Centaurea stoebe) and habitats corresponding with increasing levels of invasion. Arthropods were sampled using a diverse array of sampling methods. Arthropod data were analyzed both at the community and trophic level. Native plant species richness and percent cover values were significantly different between uninvaded and invaded habitats, but no differences were observed in plant diversity and evenness. Invasion by C. stoebe did not reduce arthropod morphospecies diversity estimates. Overall arthropod abundance however and proportional abundance by trophic level were significantly influenced by extent of invasion. Arthropod detritivores, predators, and biological control herbivores were positively related to higher levels of invasion by C. stoebe whilst native herbivores and omnivores responded negatively. Further, invasion by C. stoebe altered arthropod species assemblages suggesting that this weed impacts arthropod community organization. Centaurea stoebe likely impacts intermountain grassland plants and arthropods through both direct and indirect pathways dependent on the trophic level. This case study explores some of these potential interaction pathways and illustrates the profound and likely permanent impacts an exotic plant species will have on an ecosystem. Importantly, arthropods are excellent bioindicators of impacts related to plant invasions in grassland systems.

植物入侵或可影响整个节肢动物（arthropod）群落，但现有研究多聚焦于害虫防治或特定目标植物物种。本数据集采集自美国蒙大拿州西部，研究人员对比了未入侵斑点矢车菊（spotted knapweed，Centaurea stoebe）的山间草原生境与入侵程度递增的同类生境中的植被及节肢动物群落。研究人员采用多种采样方法获取节肢动物样本，并从群落与营养级两个维度对节肢动物数据开展分析。未入侵与入侵生境的本土植物物种丰富度及盖度百分比存在显著差异，但植物多样性与均匀度并无明显区别。斑点矢车菊的入侵并未降低节肢动物形态种多样性的估算值。不过，节肢动物总丰度及其营养级相对丰度均受入侵程度的显著影响。节肢动物中的腐食者、捕食者与生防植食者类群与斑点矢车菊的高入侵程度呈正相关，而本土植食者与杂食者类群则呈负相关。此外，斑点矢车菊的入侵改变了节肢动物物种组成，表明该外来杂草会影响节肢动物群落结构。斑点矢车菊或通过依赖于营养级的直接与间接途径，对山间草原的植物与节肢动物群落产生影响。本案例研究探讨了部分潜在的互作途径，并阐明了外来植物物种对生态系统可能造成的深远且持久的影响。尤为重要的是，节肢动物是草原生态系统中植物入侵相关影响的优质生物指示物。