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Insect Flower Visitation Frequency and Seed Production in Relation to Patch Size of Viscaria vulgaris (Caryophyllaceae)

Ola Jennersten and Sven G. Nilsson
Oikos
Vol. 68, No. 2 (Nov., 1993), pp. 283-292
Published by: Wiley on behalf of Nordic Society Oikos
DOI: 10.2307/3544841
Stable URL: http://www.jstor.org/stable/3544841
Page Count: 10
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Insect Flower Visitation Frequency and Seed Production in Relation to Patch Size of Viscaria vulgaris (Caryophyllaceae)
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Abstract

We examined frequency of pollinator visits, seed set, and seed predation in relation to plant patch size of the perennial caryophyllaceous herb Viscaria vulgaris in two areas in southern Sweden. The Dalsland area had approximately ten times more Viscaria plants per unit area than the Småland area. Long-tongued bumblebees and to a lesser extent Lepidoptera were the most important pollinators in both areas. Honeybees and bumblebees with short proboscides were mainly nectar robbers and/or pollen collectors. Insect visitation per Viscaria plant and patch were either unrelated or negatively correlated. However, bumblebee visitation was twice as high in the Dalsland area compared to Småland, while no such difference was found in Lepidoptera. Despite similar visitation rates and similar potentials for seed set, natural seed set increased with patch size. Thus, a pollinator may, on average, deposit more Viscaria pollen per flower visit in large patches than in small patches. Fruit set, i.e. the proportion of flowers setting fruits, was higher during wet years than during dry years and differed with plant size in four out of five years, suggesting resource limitation. Fruit set therefore is not a reliable measurement of pollination effectiveness in this species. Seed-feeding insect larvae were more abundant in large patches and consumed more than 60% of seed capsules in the largest patches. We conclude that Viscaria plants in large patches produce more seeds but also suffer increased risk of being attacked by seed-eating insects or infected by disease.

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