In order to make sensible interpretations of British biogeographical data it is necessary to be conversant with relevant ecological and biological concepts. Polyploidy is significant for the biogeographer since species are often vigorous and competitive. In 1870 a new species of Spartina was observed in Southampton Water. This is a sterile hybrid cross between the American species Spartina alternifolia and a native species Spartina maritima. Stress-tolerant species reduce allocations toward vegetative growth and reproduction, and exhibit features that ensure the endurance of mature individuals in harsh environments. Fugitive species of algae, such as those belonging to the genera Ulva and Enteromorpha, which rapidly colonize disturbed sites, are equivalent to J. F. Grime’s ruderal type. Species which are widely distributed may develop locally adapted populations called ecotypes that have optima and limits of tolerance adjusted to local environments. Areas of bare substrate, both on land and in the sea, are rapidly colonized by plants and animals.