Tiedeken Erin Jo, Stout Jane C
Botany Department, School of Natural Sciences, Trinity College Dublin, Dublin 2, Ireland; Trinity Centre for Biodiversity Research, Trinity College Dublin, Dublin 2, Ireland.
PLoS One. 2015 Mar 12;10(3):e0119733. doi: 10.1371/journal.pone.0119733. eCollection 2015.
Invasive alien plants can compete with native plants for resources, and may ultimately decrease native plant diversity and/or abundance in invaded sites. This could have consequences for native mutualistic interactions, such as pollination. Although invasive plants often become highly connected in plant-pollinator interaction networks, in temperate climates they usually only flower for part of the season. Unless sufficient alternative plants flower outside this period, whole-season floral resources may be reduced by invasion. We hypothesized that the cessation of flowering of a dominant invasive plant would lead to dramatic, seasonal compositional changes in plant-pollinator communities, and subsequent changes in network structure. We investigated variation in floral resources, flower-visiting insect communities, and interaction networks during and after the flowering of invasive Rhododendron ponticum in four invaded Irish woodland sites. Floral resources decreased significantly after R. ponticum flowering, but the magnitude of the decrease varied among sites. Neither insect abundance nor richness varied between the two periods (during and after R. ponticum flowering), yet insect community composition was distinct, mostly due to a significant reduction in Bombus abundance after flowering. During flowering R. ponticum was frequently visited by Bombus; after flowering, these highly mobile pollinators presumably left to find alternative floral resources. Despite compositional changes, however, network structural properties remained stable after R. ponticum flowering ceased: generality increased, but quantitative connectance, interaction evenness, vulnerability, H'2 and network size did not change. This is likely because after R. ponticum flowering, two to three alternative plant species became prominent in networks and insects increased their diet breadth, as indicated by the increase in network-level generality. We conclude that network structure is robust to seasonal changes in floral abundance at sites invaded by alien, mass-flowering plant species, as long as alternative floral resources remain throughout the season to support the flower-visiting community.
外来入侵植物会与本土植物争夺资源，并最终可能降低入侵地本土植物的多样性和/或数量。这可能会对本土互利共生关系产生影响，比如授粉。尽管入侵植物在植物-传粉者相互作用网络中往往具有高度的关联性，但在温带气候下，它们通常只在季节的一部分时间开花。除非在此期间之外有足够的替代植物开花，否则入侵可能会减少整个季节的花卉资源。我们假设一种占主导地位的入侵植物停止开花会导致植物-传粉者群落发生剧烈的季节性组成变化，进而导致网络结构发生变化。我们调查了爱尔兰四个被入侵林地中入侵性的紫花杜鹃开花期间及之后的花卉资源、访花昆虫群落和相互作用网络的变化。紫花杜鹃开花后，花卉资源显著减少，但减少的幅度因地点而异。两个时期（紫花杜鹃开花期间和之后）的昆虫数量和丰富度均无变化，但昆虫群落组成不同，这主要是由于开花后熊蜂数量显著减少。紫花杜鹃开花期间，熊蜂频繁访花；开花后，这些高度活跃的传粉者可能会离开去寻找其他花卉资源。然而，尽管组成发生了变化，但紫花杜鹃停止开花后，网络结构属性仍保持稳定：连通性增加，但定量连接度、相互作用均匀度、脆弱性、H'2和网络规模没有变化。这可能是因为紫花杜鹃开花后，两到三种替代植物物种在网络中变得突出，昆虫增加了它们的食物广度，网络层面的连通性增加就表明了这一点。我们得出结论，对于被外来大量开花植物物种入侵的地点，只要整个季节都有替代花卉资源来支持访花群落，网络结构对花卉丰度的季节性变化具有很强的抵抗力。
