On 28 May at 10:15 Kersti Riibak will defend her doctoral thesis „Importance of dispersal limitation in determining dark diversity of plants across spatial scales“.

Supervisor:
Professor Meelis Pärtel, Institute of Ecology and Earth Sciences, University of Tartu

Oponent:
Senior Research Fellow Borja Jiménez-Alfaro, PhD -University of Oviedo, Spain

Summary:
The ultimate goal of nature conservation is to avoid biodiversity loss. However, biodiversity is often only partially realized in local sites, i.e. communities are not complete. As only diverse communities can offer various nature’s benefits to people, such as pollination and natural pest control of (cultural) plants, it is essential to know why some species are absent from suitable sites and constitute dark diversity. In this thesis, we aimed to estimate the extent to which poor dispersal ability of plants (low seed abundance and short dispersal distance) may cause species absences from suitable sites in Central and Northern Europe and within grasslands ecosystems in the Baltic Sea Region. Additionally, we explored how the importance of dispersal limitation depends on local environmental conditions and human activities. We estimated dark diversity by analysing species co-occurrence patterns; to estimate dispersal abilities, we used various plant characteristics influencing seed dispersal. Our results showed that dark diversity species typically produced fewer seeds and dispersed shorter distances than observed species, indicating that poor dispersal abilities caused absences of many suitable species. The importance of dispersal limitation decreased with more stressful environments and with human activities. Species with good dispersal abilities belonged more likely to dark diversity in agricultural landscapes characterized by small areas of suitable grasslands. Overall, this thesis shows that species᾽ dispersal abilities largely determine completeness of plant communities. To increase biodiversity in agricultural landscapes, it is important to promote successful seed dispersal of native species between isolated grassland patches. This can be archived by increasing the area of grasslands (which also prevents the “loss” of seeds to unsuitable sites) and through moderate grassland management (e.g. grazing and mowing).