Jennersten Ola, Kwak Manja M
Department of Zoology, Uppsala University, Box 561, S-751-22, Uppsala, Sweden.
Department of Plant Biology, University of Groningen, P.O. Box 14, NL-9750 AA, Haren (Gn), The Netherlands.
Oecologia. 1991 Mar;86(1):88-98. doi: 10.1007/BF00317394.
We studied bumblebee foraging on two sympatrically and simultaneously flowering species, Melampyrum pratense (Scrophulariaceae) and Viscaria vulgaris (Caryophyllaceae) during the flowering season of Viscaria in south-west Sweden. We distinguished between healthy and Ustilago-infected Viscaria plants. Both species shared the main insect visitor, queens of Bombus hortorum, which collected nectar from both species but pollen from Melampyrum only. The pattern of visitation changed over the season: bumblebees preferred Viscaria early on, but changed to Melampyrum later in the season, probably because of the higher sugar content of Melampyrum nectar and the possibility of collecting both nectar and pollen from the same flower. Pollen collecting is probably of increasing importance since the need of pollen for the developing larvae will increase with time. Flowers of Viscaria received fewer visits in plots with other species than in pure Viscaria plots during one year and received more visits early than late in the season during both years. Melampyrum flowers received similar amounts of visits in mixed and pure environments. They also received more visits early than late, although this was probably a result of pollinator satiation since Melampyrum became very abundant with time. Ustilago-infected plants received far fewer visits but because of its long flowering time the proportion of open flowers receiving visits was still high. Viscaria flowers received significantly more visits than flowers of other species when bumblebees made heterospecific flower visits from Ustilago-infected plants; thus Ustilago spores were probably effectively dispersed from infected to healthy plants by the pollinators. The mechanism behind competition for pollination in this system was competition through pollinator preference, since the visitation rate to Viscaria actually decreased, but also competition through improper pollen transfer (grains of both species were found on the bodies of bumblebees) since the incidence of switching between the two species increased, probably resulting in an increased misplacement of conspecific pollen grains with time.
我们研究了在瑞典西南部粘毛卷耳开花季节，熊蜂在两种同域且同时开花的植物上的觅食行为，这两种植物分别是草原山萝花（玄参科）和粘毛卷耳（石竹科）。我们区分了健康的和被黑粉菌感染的粘毛卷耳植株。这两种植物都有主要的访花昆虫——园熊蜂的蜂后，它从这两种植物上采集花蜜，但只从草原山萝花上采集花粉。访花模式在整个季节中发生了变化：熊蜂在早期更喜欢粘毛卷耳，但在季节后期转向草原山萝花，这可能是因为草原山萝花花蜜的含糖量更高，而且有可能从同一朵花上采集花蜜和花粉。随着发育中的幼虫对花粉的需求随时间增加，采集花粉可能变得越来越重要。在一年中，与其他物种混生的地块中，粘毛卷耳花受到的访花次数比纯粘毛卷耳地块少，并且在两年中，该物种的花在季节早期比晚期受到更多访花。草原山萝花在混生和纯生环境中受到的访花次数相似。它们在早期也比晚期受到更多访花，不过这可能是传粉者饱足的结果，因为随着时间推移草原山萝花变得非常繁茂。被黑粉菌感染的植株受到的访花次数要少得多，但由于其开花时间长，开放花朵中受到访花的比例仍然很高。当熊蜂从被黑粉菌感染的植株上进行异花访花时，粘毛卷耳花受到的访花次数明显多于其他物种的花；因此，黑粉菌的孢子可能通过传粉者有效地从受感染植株传播到健康植株上。该系统中授粉竞争背后的机制是通过传粉者偏好进行的竞争，因为粘毛卷耳的访花率实际上下降了，而且还存在通过不当花粉转移进行的竞争（在熊蜂身体上发现了两种植物的花粉粒），因为两种植物之间的转换发生率增加，可能导致随着时间推移同种花粉粒的错置增加。
