Department of Biological Sciences, Macquarie University, North Ryde, NSW, Australia,
Oecologia. 2013 Oct;173(2):493-506. doi: 10.1007/s00442-013-2633-8. Epub 2013 Mar 20.
Release from natural enemies is considered to potentially play an important role in the initial establishment and success of introduced plants. With time, the species richness of herbivores using non-native plants may increase [species-time relationship (STR)]. We investigated whether enemy release may be limited to the early stages of invasion. Substituting space for time, we sampled invertebrates and measured leaf damage on the invasive species Senecio madagascariensis Poir. at multiple sites, north and south of the introduction site. Invertebrate communities were collected from plants in the field, and reared from collected plant tissue. We also sampled invertebrates and damage on the native congener Senecio pinnatifolius var. pinnatifolius A. Rich. This species served as a control to account for environmental factors that may vary along the latitudinal gradient and as a comparison for evaluating the enemy release hypothesis (ERH). In contrast to predictions of the ERH, greater damage and herbivore abundances and richness were found on the introduced species S. madagascariensis than on the native S. pinnatifolius. Supporting the STR, total invertebrates (including herbivores) decreased in abundance, richness and Shannon diversity from the point of introduction to the invasion fronts of S. madagascariensis. Leaf damage showed the opposite trend, with highest damage levels at the invasion fronts. Reared herbivore loads (as opposed to external collections) were greater on the invader at the point of introduction than on sites further from this region. These results suggest there is a complex relationship between the invader and invertebrate community response over time. S. madagascariensis may be undergoing rapid changes at its invasion fronts in response to environmental and herbivore pressure.
天敌的释放被认为可能在引入植物的初始建立和成功中发挥重要作用。随着时间的推移，利用非本地植物的食草动物的物种丰富度可能会增加[物种-时间关系（STR）]。我们调查了天敌的释放是否可能仅限于入侵的早期阶段。我们用空间代替时间，在引入地以北和以南的多个地点对入侵物种马达加斯加千里光（Senecio madagascariensis Poir.）的无脊椎动物和叶片损伤进行了采样。无脊椎动物群落是从野外的植物中收集的，并从收集的植物组织中培养。我们还对本地同属植物皱叶千里光（Senecio pinnatifolius var. pinnatifolius A. Rich.）进行了无脊椎动物和损伤采样。该物种作为控制变量，以解释可能沿纬度梯度变化的环境因素，并作为评估天敌释放假说（ERH）的比较。与 ERH 的预测相反，在引入的马达加斯加千里光（S. madagascariensis）上发现的损伤和食草动物丰度和丰富度大于本地的皱叶千里光（S. pinnatifolius）。支持 STR，总无脊椎动物（包括食草动物）从引入点到马达加斯加千里光（S. madagascariensis）的入侵前沿的丰度、丰富度和 Shannon 多样性减少。叶片损伤则呈现相反的趋势，在入侵前沿的损伤水平最高。在引入点，相对于外部收集，培养的食草动物负载（而不是外部收集）在入侵者上更大。这些结果表明，随着时间的推移，入侵种与无脊椎动物群落的反应之间存在复杂的关系。马达加斯加千里光（S. madagascariensis）可能在其入侵前沿发生快速变化，以应对环境和食草动物的压力。
