VARIATION WITHIN COMMON GROUNDSEL, SENECIO-VULGARIS L .2. LOCAL DIFFERENCES WITHIN CLIFF POPULATIONS ON PUFFIN ISLAND

Differences of height between plants from subjectively determined exposed and sheltered sites were examined in 2 cliff populations of S. vulgaris L. from Puffin Island, Anglesey, N. Wales. Under glass, the relative dwarf habit of exposed plants from a northern cliff site was retained in their progeny throughout development, but for southern cliff material there was no difference in height between progenies of exposed and sheltered plants at maturity. It was inferred that within the northern cliff site, genetic variability seems to parallel variation in exposure. But in the southern cliff site response to different levels of exposure is mainly facilitated by a wide measure of developmental flexibility for height. It is suggested that the apparent difference of adaptive strategy between the 2 cliff populations some 500 m apart may be explained in terms of disparate wind speeds in the respective sites. The northern cliffs are particularly exposed to strong winds and under these conditions it is possible that genetic adaptations to the separate micro-environments enhances survival. The reported predominant self-pollination within S. vulgaris is considered in discussion to be of value to an ephemeral as a means of adapting it to the local micro-habitats in a heterogeneous environment, so perpetuating the between plant variability. There are indications that the observed pattern of localized genetic variation on Puffin Island, both between and within populations, evolved over the last 20 yr.