AGE AND SIZE OF EUROPEAN SALT-MARSHES AND THE POPULATION GENETIC CONSEQUENCES FOR GROUND BEETLES

Enzyme and dispersal polymorphisms of the saltmarsh carabid beetles Po gonus chalceus and Dicheirotrichus gustavii were studied in European p opulations varying in size and in isolation in space and time. D. gust avii, a constantly fullwinged species, has a larger genetic diversity and a smaller genetic differentiation between populations than the win g-polymorphic P. chalceus. Clear relationships between population or s ite characteristics and genetic structure were not observed, except fo r the special position taken by some small populations in both species . The dispersal power of P. chalceus in small populations is larger th an in large populations, suggesting that these populations are unstabl e and/or young. Small populations, however, do not always show a lower genetic diversity than large populations, as would be expected from g enetic drift. Dispersal power in P. chalceus declines with increasing age of the saltmarsh, probably due to continuous emigration of winged individuals. Age and size of saltmarshes, although difficult to study independently, both appear to be important in determining the genetic structure of saltmarsh beetles. Maximum diversity in both parameters i s therefore recommended as an optimal nature conservation strategy.