POLLEN FLOW BETWEEN CONNECTED AND ISOLATED FLOWER PATCHES

Abstract

Pollen flow between artificial patches of Scabiosa columbaria (Dipsacaceae), mainly pollinated by syrphids, was studied in a seminatural environment. Three linearly arranged patches of 30 heads each were used. The central patch served both as pollen donor and receptor patch (complete flowers), the other two patches served only as receptor patches (emasculated flowers and female flowers). The central patch was connected over a distance of 25m with one receptor patch by a corridor of flowers. The plant species of the corridor varied: either S. columbaria female heads, S. columbaria male heads, Origanum vulgare inflorescences or Aster multiflorus heads were used. The corridor species shared visitors with S. columbaria. The second receptor patch was not connected with the donor patch and served as a control. Syrphid species did not differ in hop size (distance between two subsequently visited heads) if the corridor consisted of S. columbaria female heads. In the Aster corridor, syrphid species made larger hops than in the Scabiosa corridor. Despite the fact that a fair amount of pollen was deposited on the female heads in the corridor, pollen flow was increased significantly in 4 out of 10 experiments if the receptor patch was connected with a corridor containing S. columbaria male or female heads. In only one experiment a significant decrease in pollen deposition in the connected patch (connected with a female S. columbaria corridor) was observed. Pollen flow was significantly reduced in 2 out of 9 experiments with Aster or Origanum as corridor species and was increased significantly only once. A significant increase of heterospecific pollen deposition was observed if the corridor species was not conspecific.