School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588, USA.
Ecology. 2012 Aug;93(8):1787-94. doi: 10.1890/11-1583.1.
A current challenge in ecology is to better understand the magnitude, variation, and interaction in the factors that limit the invasiveness of exotic species. We conducted a factorial experiment involving herbivore manipulation (insecticide-in-water vs. water-only control) and seven densities of introduced nonnative Cirsium vulgare (bull thistle) seed. The experiment was repeated with two seed cohorts at eight grassland sites uninvaded by C. vulgare in the central Great Plains, USA. Herbivory by native insects significantly reduced thistle seedling density, causing the largest reductions in density at the highest propagule inputs. The magnitude of this herbivore effect varied widely among sites and between cohort years. The combination of herbivory and lower propagule pressure increased the rate at which new C. vulgare populations failed to establish during the initial stages of invasion. This experiment demonstrates that the interaction between biotic resistance by native insects, propagule pressure, and spatiotemporal variation in their effects were crucial to the initial invasion by this Eurasian plant in the western tallgrass prairie.
当前生态学的一个挑战是更好地理解限制外来物种入侵性的因素的规模、变化和相互作用。我们进行了一项析因实验，涉及食草动物的操纵（杀虫剂水与仅水对照）和引入的非本地苍耳（刺蓟）种子的七个密度。该实验在未被苍耳入侵的美国大平原中部的八个草原地点用两个种子批次重复进行。本地昆虫的取食显著降低了蓟的幼苗密度，在最高繁殖体输入时造成密度的最大降低。这种食草动物效应的幅度在不同地点和不同种群年之间有很大差异。食草作用和较低繁殖体压力的结合增加了新的苍耳种群在入侵的初始阶段无法建立的速度。这项实验表明，本地昆虫的生物抗性、繁殖体压力及其影响的时空变化之间的相互作用，对这种欧亚植物在西部高草草原的初始入侵至关重要。
