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Pollination ecology of Scabiosa columbaria : a comparison between small and large populations

Ozinga, W. and Bakker, L. (1995) Pollination ecology of Scabiosa columbaria : a comparison between small and large populations. Master's Thesis / Essay, Biology.

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Abstract

We studied the pollination ecology of Scabiosa columbaria (Dipsaceae) in relation to population size. We observed visitors in 9 populations in the central and southern part of the Netherlands. We found a positive relationship between population size of S. columbaria and insect species richness. S. columbaria was frequently visited in the field, about 25 visits per head per day was found. Only a small number of the insect species visiting S. columbaria were common found. The syrphid Eristalis tenax and the nightmoth Autographa gamma, which flies at daytime, were clearly the most common visitors. Bombus pascuorum had the highest foraging speed of the flower visitors, as well in number of flowerheads as number of flowers visited per minute. In the field however B. pascuorum rarely visited S. columbaria, but it was a common visitor on Centaurea jacea. Pieris rapae had a higher foraging speed than E. tenax. E. tenax, A. gamma and P. rapae switched the same times from plant species, every fifth visited flower(head) was of an other species. The amount of visits on S. columbaria was significant larger for E. tenax than for A. gamma and P. rapae. In a population where S. columbaria occupied a smaller part of the vegetation for E. tenax a relatively lower number of visits on S. columbaria was found. B. pascuorum carried the largest number of pollen on its body. Butterflies carried a very low number of pollen, A. gamma and P. rapae carried on average 19 ± 7 and 72 ± 33 grains. The amount of S. columbaria pollen in the pollen load of insects foraging on S. columbaria was for all species low, about 25 %. This was reflected in the amount of pollen of S. columbaria on the stigma's, about 20%. Species with many pollen on stigma's of S. columbaria were Centaurea ssp., Origanum vulgare, Daucus carota and Compositae. The pollen of Knautia arvensis, a related species, were not distinguishable from pollen of S. columbaria, their part was probably underestimated. The mean deposition rate was for E. tenax 8.5 ± 3.0 and B. pascuorum 3.8 ± 0.6 grains per stigma per minute. The number of deposited pollen in the field increased steadily from about 09.00 am during the rest of the day, till in the mid of the afternoon about 9 pollen per stigma (only stigma's which receive pollen were included) were deposited. Then the number of pollen remains the same. E. tenax and P. rapae only flew short distances, more than 90 % less than 2 meter. P. rapae made 15 % of its flights over distances larger than 10 meter. With fluorescent dye powder the possible transport distance of pollen was traced. Most of this powder was distributed within 10 meter of the donor plant. A small amount however was distributed over a distance more than 100 meter. he number of visits and the number of pollen deposited on the stigma's of S. columbaria seems to be sufficient for seedset, but the quality is a question. Qualitative aspects of pollination seem to be more important than quantitative aspects for S. columbaria. This is caused by the generalistic behaviour of the flower visitors. Differences in quality of pollination were not related to population size of S. columbaria, but could be more related to density of flower heads of S. .columbaria in relation to other flowering plants.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:48
Last Modified: 15 Feb 2018 07:48
URI: http://fse.studenttheses.ub.rug.nl/id/eprint/10105

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