Plant DispersalDynamics of plant dispersal-related traits in fragmented European habitats: consequences for species survival and landscape management. |
For plant species living in a fragmented landscape, dispersal ability is important for the persistence of populations as it directly affects colonization probabilities and amount of gene flow. With increasing habitat fragmentation, populations become more isolated and can be regarded as islands in an otherwise uninhabitable area. In this situation, seeds with high dispersal ability are likely to be wasted from the population, and natural selection for reduced dispersal potential may lead to completely isolated populations with a high risk of extinction. Thus, while an increase in migration is necessary, selection might lead to the opposite. In this project we will analyse the natural variation and genetic basis of plant dispersal capacity and develop and improve models that predict population dynamics. This is very relevant for the sustainable conservation of biodiversity in fragmented European landscapes, and indispensable for setting up management plans.
The project "Plant Dispersal" analysed the natural variation and genetic basis of plant dispersal capacity, and developed and improved models that predict population dynamics in fragmented European landscapes.
The relationship between the extent of fragmentation and variation in seed dispersal traits in European landscapes varies across species, and across different regions in the same species. In addition, the patterns are environment-dependent and differ according to the spatial scale. At the same spatial scale, the evolutionary consequences of fragmentation vary with the previous extent of fragmentation.
The possibility of selection depends on the heritability of dispersal-related traits. Dispersal ability was found to be a result of environmental conditions as well as genetics. Currently, however, models of evolution of dispersal do not take into account an environmental effect on dispersal capacity.
Long-distance dispersal is a rare event, which is difficult to measure real-time, and also difficult to predict or model. At the same time it may have a disproportional contribution to dispersal and gene flow. The work that we carried indicates that tracing the expansion of genotypes in a selfing species with molecular markers may be a very good way to quantify both.
In summary, the effects of increased habitat fragmentation on dispersal ability of plant species are not straightforward, and, as a result, simple "rules of thumb" do not exist. First of all, habitat fragmentation is only one aspect of the dramatic changes in land use in the European landscapes during the last century. For any particular species, the effects of changes in habitat quality or disturbance may be more pronounced than the effect of a reduction in area. We generally do not know what aspects of former land use (including human activities) were beneficial for plant species.
The history of populations is a confounding factor. The fact that many existing plant and animal populations still persist makes it difficult to identify the problems with regard to dispersal and colonisation of new or empty habitat. Historical data are often existing but not readily available.
Many plant species already have life history adaptations that make them less dependent on continuously successful dispersal (but do not make them insensitive to the effects of decrease in habitat area or quality). The effectiveness of these adaptations, and their consequences for metapopulation models, has not been studied.
The selective forces for dispersal depend partly on genetic load, the effect of which will increase in small populations. Theory indicates that populations with a strongly reduced population size may suffer from genetic load, while equally small populations of species that usually occur in small populations, may have no problem (since they have purged their load). We do not know how generally this will hold in the situation of rapid landscape change.