Adaptation in perennial coastal plants — with particular reference to heritable variation in Puccinellia maritima and Ammophila arenaria

Abstract

Perennial species invading the early stages of primary successions face constant, and often rapid, change in their biotic and abiotic environment. The relative abilities of different species to adapt to this change is reflected in the zonation patterns which characterize coastal vegetation. Variation in those species with wide ecological amplitudes, particularly in populations near the boundary of the realized niche, is likely to be particularly revealing.

The pattern of heritable variation in Puccinellia maritima on salt marshes indicates directional selection for traits increasing plant vigour and ‘competitive ability’; presumably the effect of increasing plant density. Adaptation is by both genetic differentiation and phenotypic flexibility, the former being evident in adjacent grazed and ungrazed marshes and the latter in a mosaic of tall and short vegetation types. By contrast variation in Ammophila arenaria on dunes exhibits high levels of phenotypic flexibility, growth in a range of environments indicating that plants from fore-dune populations are higher ‘responders’ than those from mature dunes.

Among the implications of these results, and by comparison with other species, is the fact that, ironically, niche expansion for some salt marsh perennials may require the evolution of an annual strategy, and that a Darwinian selection model may help to explain variation in Ammophila’s apparent vigour in dunes of different age.

Nomenclature follows Tutin et al.: Flora Europaea (1964–1980).

I am grateful to several colleagues and students, past and present, who have helped with the studies of Puccinellia and Ammophila and I am particularly indebted in this respect to Richard Scott.