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Pollination ecology of Succisa pratensis: a comparison between populations differing in size and flower diversity

Hunneman, H. (2003) Pollination ecology of Succisa pratensis: a comparison between populations differing in size and flower diversity. Master's Thesis / Essay, Biology.

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In this study, the effects of population structure on the pollination success of Succisa pratensis Moench (Dipsacaceae) were investigated. Pollination services and their effects on plants' reproductive success are compared for four (natural) populations of S. pratensis that differ in size and flower diversity. Pollination services include quantity (total visitation frequency) as well as quality (per visit efficiency) components of pollination. In all populations, Succisa was visited by a large variety of insect species (22 species in total), belonging to the Syrphidae, other Diptera, Hymenoptera and Lepidoptera. Syrphid flies were the main visitors of Succisa during the whole flowering period, especially members of the Eristalinae (a subfamily of the Syrphidae). Helophilus trivittatus, Eristalis horticola, Helophilus pendulus, Eristalis tenax/pertinax and Eristalis arbustorunilnemorum (all members of the Eristalinae, arranged according to their abundance) showed by far the highest numbers of individuals at the sites. These syrphid fly species are (very) common in The Netherlands. On average, a flower head of Succisa received between 24 and 83 insect visits a day. Such a visitation rate is quite high in comparison with other flowering plant species and this means that Succisa is an attractive plant species for insects. The visitation rates (quantity component of pollination) did not differ between populations varying in size and flower diversity. The most frequent Succisa visitors carried a high proportion of heterospecific pollen on their bodies (ranging from 22 to 80%) due to their generalistic feeding behaviour. Heterospecific pollen consisted mainly of Asteraceae pollen grains. The composition of the pollen loads of the visiting insects is reflected very well in the pollen deposited on Succisa stigmas. A small fraction of conspecific pollen was deposited on the stigmas of Succisa in all populations. In contrast to the quantity component of pollination, this quality component differed between the studied populations. Large populations received a higher proportion of conspecific pollen (45% and 64%) than small ones (17% and 18%). Presumably, this difference is the result of passive flower constancy of the most frequent Succisa visitors. Therefore, in The Netherlands, qualitative aspects of pollination seem to be more important in determining differences between populations of Succisa than quantitative aspects. No difference in the proportion of conspecific pollen deposited was found between populations differing in flower diversity. This is probably caused by large flight distances of the visiting insects. Long foraging distances of the pollinators of Succisa may lead to substantial gene flow by pollen between Succisa populations. This reduces the threat of genetic erosion to Succisa populations. The difference in proportion of conspecific pollen deposited does not lead to differences in seed germination rates between populations. The germination rate was low in all populations (<50%). Probably, this is (partly) caused by the deposition of large amounts of heterospecific pollen, even in large Succisa populations. Thus, Succisa plants suffer from competition through interspecific pollen transfer. Artificial hand pollinations are needed to determine the susceptability of Succisa to the deposition of heterospecific pollen, unambiguously.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:45
Last Modified: 15 Feb 2018 07:45

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