Cascading Effects of Mutualistic Interactions: From Insect Flower Visitation to Plant Community Dynamics

Ecologists have for a long time been interested in how negative plant-animal interactions, such as herbivory and seed predation affect the population dynamics of plant species, their distribution on small and large spatial scales, and the plant community species composition and diversity. Positive plant animal interactions, such as pollination, has received considerable attention with regards to its effects on plant reproduction, but very little attention with regard to plant population dynamics and absol utely no empirical attention with regard to plant community composition and diversity. This lack of attention to consequences of plant-pollinator interactions for levels beyond the reproduction of individual plants is surprising. On purely pragmatic grou nds pollinators conceivably play a fundamental role for plant community composition and diversity through their contribution to seed production of animal-pollinated plant species. The central core of this project is to assess how the species diversity an d abundance of bumblebees within the pollinator assemblage may affect the frequency of pollination-specialised plant species, particularly adapted to bumble bee pollination, within communities. It is conceivable, but hereto completely unknown, that the po pulation densities of bumble bee-specialized plant species, and their frequency within plant communities, varies spatially with the functional composition of the pollinator assemblage. A central methodology of this project is an experiment that manipulat es the relative frequency of bumblebees visiting flowers of plant species. The project measures the reproductive and demographic responses of several plant species adapted to bumblebee pollination and species with a more generalist pollination to this exp erimentally induced change of the pollinator assemblage.