Dynamics Of Pollination Network In An Alpine Meadow

A traditional view of diverse floral traits which reflected specialization onto different pollinator groups. This adaptive explanation of floral diversity assumes different pollinators promote directional selection for different floral traits, which led to the formation of pollination syndrome concept, referring to suites of floral traits evolved in relation to the attraction and utilization of a specific group of animals as pollinators, which has similar floral preference. However, the assumptions of specialization and the role of pollinators in the evolution of floral traits have been questioned recently by broad community surveys concerning community context variation in plant-pollinator interactions, which suggest generalization may be as important as specialization in pollination systems. In this study, we mainly focused on the basic structure and dynamic pattern of plant-pollinator network, by a community study on plant-pollinator interactions at an alpine meadow in Hengduan Mountains, China over four consecutive years.First, to illustrate whether specialization or generalization is dominated in pollination system, we investigated mutualism network between plants and pollinators. Comparing four annual binary polliantion networks, we found all networks were quite nestedness. Plants and polliantors were asymmestric assemblaged in networks. Most plants were pollinated by generalist pollinators. Although the composition of network was highly dynamic, networks were in relative stable structure. The core group that consisted by generalized species, were relatively more stable than peripheral species. The identical species linked to most partners in annual networks. This result indicated the pollination enviroment was temporally stable despite high species turnover.Beside the duration of species, the duration of links is important to the dynamic of ecological mutualism networks. If pollinator-mediated selection is one major force driving the evolution of flowers, the selective role of the pollinators could be diminished if plant-pollinator interactions are highly variable across years. We investigated quantitative network for three consecutive years, to explore the turnover of the identical links. The identical links tended to have similar link strength between pair years. And they were less replaced according to higher strength. However, the stable links between generalized pollinators and relative specialized plants also suggested the network asymmetry. The variations of visit composition were decreased with pollinator number, suggesting that generalized plants were also experienced relative stable visit partition compared to specialized plants. We thus conclude that pollination network also remain stable at link level. The tight links between generalized pollinators and relative specialized plants emphasized the importance of specialized species to disturb resistance. We suggested that while plant species might be pollinated by various pollinators, the stable tight links between bumblebees and plants might result in a coexistence pattern, in which temporally stabilized preferences of generalized pollinator sustained a wide range of plants.Finally, plants which share same pollinator migh experience disturbance of heterospecific pollen from sympatric flowering plants. However, whether floral morphology or pollination enviroment has an impact on heterospecific pollen transfer has received little attention. We investigated the heterospecific pollen ratio and species number on stigmas in47plant species, and the relationship between flower morphology and pollinator composition. The exposure degree of stigma was positivly related to heterospecific pollen ratio, while the pollen species number was related to pollination enviroment. Our results suggested the more exposure stigma in unrestrictive flowers could account for their higher heterospecific pollen receipt while it might increase outcrossing rate, and generalized plants which employed various pollinators were not influrenced by heterospecific pollen seriously.