Demographic studies of Anthyllis vulneraria L. in The Netherlands. II. Population density fluctuations and adaptations to arid conditions, seed populations, seedling mortality, and influence of the biocenosis on demographic features

During a period of eight years demographic studies were made of a coastal population of Anthyllis vulneraria L. var. langei Jalas and of an inland population of its var. vulneraria. The coastal population was found in open dune vegetation on a sandy soil, whereas the inland population occurs in a relatively dense, calciphilous grassland vegetation on a loamy soil. Intermittent periods of drought occur both along the coast and inland, but the dune biotope is considerably more arid than the inland one. In the interior, the more fertile soil supports a much denser and richer biocenosis than does the dunal habitat, and this has important consequences for the population biology. In the coastal region much more extreme population density fluctuations take place, whilst the correlation between these fluctuations and the fluctuations of the abiotic environment (drought) are more evident than they are inland. The dunal form is obviously better adapted to periodic droughts, i.e., to an abiotic factor which is not dependent on population density. In the interior, such biotic factors as competition and predation have a much greater influence owing to the more complex mutual relations between individuals and to the richer composition of the total biocenosis. There are differences in germination ecology, in mortality of seedlings and juvenile plants, in reproduction strategy, and in seed predation between the two populations studied. The coastal populations and the inland ones are each to a large extent build up by pure lines on account of the almost obligatory autogamy; these lines exhibit genetically controlled differences in pubescence.