Colonization dynamics and relative abundance of three plant species (Antennaria dioica, Hieracium pilosella and Hypochoeris maculata) in dry semi-natural grasslands

The objective of this study was to examine how population recruitment depends on seed size, and if relative abundance depends on colonization, in three plant species inhabiting dry semi-natural grasslands. All three species, Antennaria dioica, Hieracium pilosella and Hypochoeris maculata belong to the same family, Asteraceae, and possess similarly structured wind-dispersed fruits, achenes with pappus. They occupy the same range of habitats, but an not equally abundant. The seed size hierarchy is Hypochoeris > Hieracium > Antennaria. Results from experiments suggest that recruitment is promoted by small disturbances, but limited also by seed availability. Seed size differences explain interactions during recruitment; Hypochoeris "wins" over the other two species, and Hieracium wins over Antennaria. Seed arrival order did not alter this hierarchy. A model of relative abundance of the species was developed, based on observed differences in recruitment and seed output from local populations. The model was able to predict observed relative abundance patterns at a large spatial scale, especially at marginal sites along road verges (Hieracium > Hypochoeris > Antennaria), but not at smaller scales, where Antennaria was more frequent than Hypochoeris. The results support a metapopulation approach to abundance patterns in landscapes, and, more specifically, they support the hypothesis that species abundance reflects colonizing ability. An additional implication is that single source populations may be of great importance for species persistence in landscapes, a conclusion which has bearing on development of conservation and management plans for endangered habitats.