Jacques Meriguet

Functional Diversity of Plant–Pollinator Interaction Webs Enhances the Persistence of Plant Communities

Pollination is exclusively or mainly animal mediated for 70% to 90% of angiosperm species. Thus, pollinators provide an essential ecosystem service to humankind. However, the impact of human-induced biodiversity loss on the functioning of plant–pollinator interactions has not been tested experimentally. To understand how plant communities respond to diversity changes in their pollinating fauna, we manipulated the functional diversity of both plants and pollinators under natural conditions. Increasing the functional diversity of both plants and pollinators led to the recruitment of more diverse plant communities. After two years the plant communities pollinated by the most functionally diverse pollinator assemblage contained about 50% more plant species than did plant communities pollinated by less-diverse pollinator assemblages. Moreover, the positive effect of functional diversity was explained by a complementarity between functional groups of pollinators and plants. Thus, the functional diversity of pollination networks may be critical to ecosystem sustainability.

Direct and indirect effects of biomanipulations on periphyton stoichiometry in shallow lakes

Periphyton is a complex mixture of algae, heterotrophic organisms (bacteria, fungi, protozoa), and dead organic matter, attached on diverse substrates in aquatic ecosystems (WETZEL 1983). In littoral regions of shallow lakes, periphyton can represent high biomasses, and several studies have shown that both benthic and pelagic food webs may strongly rely on this resource (e.g., VANDER ZANDEN & VADEBONCOEUR 2002). In the context of eutrophication of freshwater ecosystems, many lakes have switched from a clear water state, with dominance of aquatic macrophytes and high piscivorous/benthivorous-planktivorous ratios, to a turbid water state, with high biomass o f phytoplankton and dominance of benthivorous/planktivorous fishes. Biomanipulations (e. g., manipulations offood web structures by modifying fish communities) can induce a shift from stable turbid state to clear water (PERRow et al. 1997). To maintain this clear water phase, a good understanding of the processes that stabilize systems in this state is essential. In particular, the ro le of periphyton, which competes with phytoplankton and macrophytes for inorganic nutrients, light and C027 must be taken in consideration (JONES et al. 2002). Few works have studied the effect o f food-web structure o n periphyton development. By modifying grazer communities and characteristics oflakes, such as light an d nutrient availability, biomanipulations may greatly affect periphyton in many ways. In particular, following ecological stoichiometry principles, induced modifications of periphyton elemental composition (C:N:P ratios) could greatly affect some important ecological processes, such as grazer-macrophyte-periphyton interactions (CRoss et al. 2005). We analyzed differences in biomass and stoichiometry of the periphytic compartrnent in mesocosms simulating food web structure of nonbiomanipulated and biomanipulated lakes.