DYNAMICS OF LONG-DISTANCE DISPERSAL: THE SPREAD OF ASPLENIUM ADIANTUM-NIGRUM AND ASPLENIUM TRICHOMANES (ASPLENIACEAE: PTERIDOPHYTA) ON LONDON WALLS

摘要

Asplenium adiantum-nigrum L. and A. trichomanes L. have spread widely across inner London since about 1995 but have not yet colonised the district uniformly. The spacing between sites, and evidence that at most a few founding populations are involved,suggests that a sequence of long-distance dispersal events is responsible. A simple model of dispersal is proposed which predicts an exponential distribution of nearest-neighbour distances. The combined data for both species yield a good fit to such a distribution and a value of approximately 0.75 km for the mean distance between a newly-established sporophyte and the nearest potential parent plant. This leptokurtic distribution accounts for some offspring growing 5 km or more from their parent while the populated zone expands at up to 1 km per year. Assumptions underlying these conclusions are examined.