The population dynamics of Spergularia marina on a Baltic seashore meadow

Sammanfattning: This thesis presents the demography and population dynamics of the annual halophyte Spergularia marina on a Baltic seashore meadow. The object of the investigation was to study the variation in demographical attributes by using a site-by-site comparison during four consecutive years. The demographic consequences of growth form in the plant was also studied. The results show that the survivorship varies both between years and between sites. Deevey type I to HI survivorship curves were observed.The variation in reproduction between years was determined by density, but differences in the length of the flowering season highly influenced seed production in one of the sites. The population size showed great variation both in time and space. To a large extent this was determined by differential survivorship, but limitation in reproductive capacity also influenced the size and variation in population density. No density-dependent mortality was observed. Instead it is suggested that the modular growth allows for plastic responses in size, growth rate, phenology and reproductive output with density.