A major threat to European landscapes is the ongoing fragmentation of habitats. This not only causes direct loss of populations but also imposes an increased risk of extinction on species living in the remaining fragments. In such situation dispersal ability becomes a critical factor as it allows exchange of individuals and genes among fragments, which is thought to partially counteract the negative effects of fragmentation. Moreover, dispersal is a prerequisite for recolonization of empty habitats and thus of utmost importance for the stability of metapopulations. As such, dispersal is a key factor in biodiversity conservation.
For plant species living in a fragmented landscape, increased dispersal is thus likely to be advantageous and morphological characters that increase dispersal ability, such as larger fluff balls (pappus) in wind dispersed species, may be favored by natural selection. However, if the process of   habitat fragmentation continues, populations become increasingly isolated and can be regarded as islands in an otherwise uninhabitable area. In this situation, seeds with high dispersal ability are more likely to be wasted from the population and the next generations in the population will predominantly arise from seeds with low dispersal ability, resulting in selection for reduced dispersal potential. Consequently, this may cause the metapopulation to disintegrate into completely isolated populations, which increases the chance of inbreeding and genetic drift, and ultimately leads to extinction. Recent studies have indicated that this undesirable selection process may proceed relatively fast, and that changes in morphological characters of isolated populations already are observed within a few generations. However, we do not know to what extent this is taking place in Europe.

 

The project investigates the dispersal capacity of several Compositae (Asteraceae) species, including Mycelis muralis, in European landscapes with different degrees and types of habitat fragmentation along a North-South gradient. It determines populations characteristics, amount of genetic variation, and heritable variation for seed dispersal characteristics in these populations, and tries to identify (major) genes involved in seed dispersal traits. These data are used in models describing the dynamics of metapopulations. Findings are implemented into 'simple' protocols and software for analysing the current state of endangered populations and for devising effective counter-measures.

 

The results of this project will significantly contribute to understanding the dynamics of dispersal and metapopulations that are currently 'hot topics' in ecological research. In this project we determine the variation in seed dispersal traits in natural populations, in relation to the fragmentation of the habitat. Models will then predict under what circumstances dispersal-related traits are selected against. The implications of the results for nature managers and policy makers consist of improved technology to predict and manage natural areas.