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Life History Variation of Common Mullein (Verbascum Thapsus): III. Differences Among Sequential Cohorts

James A. Reinartz
Journal of Ecology
Vol. 72, No. 3 (Nov., 1984), pp. 927-936
DOI: 10.2307/2259541
Stable URL: http://www.jstor.org/stable/2259541
Page Count: 10
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Life History Variation of Common Mullein (Verbascum Thapsus): III. Differences Among Sequential Cohorts
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Abstract

(1) Two sequential cohorts of mullein (Verbascum thapsus) were studied in each of six North Carolina sites in order to assess the phenotypic and genetic responses of the populations to successional changes. The plants were grown in a common garden to determine whether there was any genetic basis to successional variation in the phenotype. The first and second cohort seed progenies sampled from each of two populations were cultivated. (2) The dynamics of the populations were closely related to the successional age of their habitats. Few seeds germinated and seedling survival was low in years after the first cohort following a disturbance. (3) Succession caused reproduction to be delayed; triennial plants were much more common in second cohorts than in first cohorts. (4) Habitat successional age determined the relative fitness of biennial and triennial mulleins. Biennials in first cohorts produced five times as much seed as triennials. Second cohort biennials and triennials had approximately the same seed production, and by the time the third cohort came to fruit, triennials produced more seed than biennials. (5) Differences between cohorts in plant size and the year of flowering were primarily environmentally induced; however, variation between cohorts in a number of other characters appeared to have a genetic basis.

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