Das Projekt "Biologie der Erhaltung von abnehmenden Gruenlandspezies: experimentelle Analyse von Populationsprozessen" wird vom Umweltbundesamt gefördert und von Universität Zürich, Institut für Umweltwissenschaften durchgeführt. In the last decades many plant species have experienced a dramatic decline in the number of populations and the remaining populations are frequently small and isolated from each other. Environmental stochasticity and genetic erosion pose considerable threats to small and isolated plant populations. Successful management of declining species to conserve plant biodiversity requires an understanding of both demographic and genetic processes at the population level and of their importance for local extinctions. The first aim of our project is to analyze the mechanisms driving the population dynamics of plant species in decline. We will investigate the relationship between environmental factors, variability of demographic parameters, population size, and risk of extinction in several short-lived grassland species. All demographic data will be integrated into stochastic matrix population models to identify critical transitions in the life cycle and estimate critical population sizes. Part of the project is a continuation of demographic studies with Gentianella germanica. This offers the chance to obtain long-term estimates of the temporal and spatial variability of demographic transition rates. They will be integrated into models to study minimum data requirements for reliable predictions of population trends and extinction risks in rare species. Results of the first phase of the project indicate that reproduction is the first component of a plant's life cycle that becomes negatively affected by reduced population size. We will investigate the relationship between population size and reproduction in a large number of declining plant species to determine critical population sizes for reproductive success. The results will be compared with results from the general demographic studies. The second aim of the project is to assess the importance of genetic variability for the population dynamics of declining species. Two different approaches will be used. First, we will study the effect of increased gene flow on the growth and survival of plants in small populations. This study has important implications for habitat management. Second, we will experimentally investigate the importance of initial genetic diversity for the success of founder populations.