Genecological studies of groundsel (Senecio vulgaris L.). IV. Rate of development in plants from different habitat types

SUMMARY In order to test the hypothesis that precocious variants might be at a selective advantage in well-weeded sites, ripen pollinated achenes of Senecio vulgaris L. were collected in eastern Britain from three populations representative of each of live habitat types (botanic gardens, field margins, inland and coastal sandy areas and shingle beaches) Some subject to weeding and cithers not. Progenies of a number of seed-parents (families) were grown in a garden trial, and life-history and reproductive characteristics were recorded, in particular the rate of development from sowing, with synchronous germination, to first fruiting. Populations from botanic gardens were characterized by families exhibiting precocious reproduction, a finding which supports oru initial hypothesis. However, a degree of variation was detected in samples from all three botanic gardens - Orford, Kew and Cambridge - confirming the results of an earlier study of groundsel in the University Botanic Garden, Cambridge. In contrast, samples from maritime shingle beaches had a slower rate of development. There was no evidence of population variation, suggesting that genetic drift or founder effects might be important or that there may be selection for a narrow range of phenotypes, in such areas. Furthermore, at Shingle Street, Suffolk, there was evidence of sharp local differentation between plants from the single beach and from an arable field margin, 50m away, located behind sea defence. The characteristics of plants from other habitat types are discussed in relation to the apparent selection pressures imposed by different land use. Our results provide evidence of trade-offs in life-history evolution, e.g. the precocious variants were comparatively dwarf at first fruiting and shorter-lived.