Displacement of a native by an alien bumblebee: lower pollinator efficiency overcome by overwhelmingly higher visitation frequency
Displacement of a native by an alien bumblebee: lower pollinator efficiency overcome by overwhelmingly higher visitation frequency
复制标题
本地大黄蜂被外来大黄蜂取代：传粉媒介效率降低，但造访频率极高
作者：
Josefin A. Madjidian;C. Morales;Henrik G. Smith
生物入侵可能对互利共生构成重大威胁。如果本地和外来访客的传粉媒介有效性不同，引入的传粉媒介可能会竞争性地取代本地同类，从而影响本地植物的授粉。自 1994 年入侵阿根廷西南部以来，引进的欧洲熊蜂 Bombus ruderatus 的数量不断增加，而本土 Bombus dahlbomi 的数量却同时减少。后者是南美洲南部温带森林唯一的本土熊蜂物种，也是特有草本植物六出花的主要传粉者。为了评估外来熊蜂持续取代本地熊蜂的影响，我们比较了两种熊蜂物种之间的传粉媒介有效性（即每次访问的传粉媒介效率和访问频率的组合），以及可能解释传粉媒介效率潜在差异的相关传粉媒介特征。本地熊熊体型较大，每朵花花费的时间也更长，与粗熊熊相比，无论是在每次访问所沉积的花粉的数量和质量方面，都是更有效的传粉者。然而，鲁德拉熊熊 (Bombus ruderatus) 比达博熊熊 (Bombus dahlbomii) 更频繁地来访花卉。因此，如今，鲁德拉熊熊 (Bombus ruderatus) 是比其本地同类更有效的 A. aurea 传粉媒介。尽管缺乏证据表明种群数量增加，但与 Bombus ruderatus 入侵之前的 Bombus dahlboii 丰度历史记录进行比较表明，A. aurea 的整体授粉强度实际上可能由于这次入侵而上升。像这样的现场实验结合了本地和外来物种丰富度的自然变化，是证明入侵的后果比以前的操纵和控制实验所表明的更为复杂的有力手段。
Biological invasions might constitute a major threat to mutualisms. Introduced pollinators might competitively displace their native counterparts, which in turn affects the pollination of native plants, if native and alien visitors differ in pollinator effectiveness. Since its invasion in 1994 into south-west Argentina, the introduced European bumblebee Bombus ruderatus has continuously increased in abundance, along with a simultaneous decrease in the abundance of the native Bombus dahlbomii. The latter is the only native bumblebee species of the temperate forests of southern South America, and the main pollinator of the endemic herb Alstroemeria aurea. In order to evaluate the impact of the ongoing displacement of the native by the alien bumblebee, we compared the pollinator effectiveness (i.e., the combination of pollinator efficiency per visit and visitation frequency) between both bumblebee species, as well as related pollinator traits that might account for potential differences in pollinator efficiency. Native Bombus dahlbomii, which has a larger body and spent more time per flower, was the more efficient pollinator compared to Bombus ruderatus, both in terms of quantity and quality of pollen deposited per visit. However, Bombus ruderatus was a much more frequent flower visitor than Bombus dahlbomii. As a consequence, Bombus ruderatus is nowadays a more effective pollinator of A. aurea than its native congener. Despite the lack of evidence of an increase in seed set at the population level, comparisons with historical records of Bombus dahlbomii abundances prior to Bombus ruderatus’ invasion suggest that the overall pollination intensity of A. aurea might in fact have risen as a consequence of this invasion. Field experiments like these, that incorporate the natural variation in abundance of native and alien species, are powerful means to demonstrate that the consequences of invasions are more complex than previous manipulated and controlled experiments have suggested.