Spatial distribution and the performance of individual plants in a natural population of Silene dioica.

1) A natural population of the perennial herb Silene dioica was mapped at intervals over the course of a year. The 'space available' to each plant was estimated by a Thiessen polygon, defined by the position of the plant's neighbours. 2) Germination and recruitment of seedlings appeared to be unrelated to the position of individuals with respect to their neighbours. 3) Various measures of plant growth were strongly correlated with polygon area in some seasons, suggesting that competition was occurring between individuals for spatially distributed resources. Plasticity allowed plants to exploit the available area, regardless of polygon shape or the number of neighbours defining a polygon. 4) In the early spring phase of seedling establishment, growth appeared to be enhanced and seedlings lived longer when they were close to neighbours. In late spring this effect was replaced by the more rapid growth of individuals in the larger polygons, i.e. with more distant neighbours. This sequence of events is consistent with the onset of competition for resources in late spring. 5) These effects were observed despite heterogeneity in the environment and variation in individual response.