Abstract
Processes like grazing and productivity influence autotroph species richness. Grazing may reduce plant species richness through the loss of rare species, but increases richness if preferred food plants are competitively dominant. Conceptual models predict a reversal of grazing effects on plant species richness between nutrient-poor and nutrient-rich ecosystems, since nutrients increase the ability of plants to compensate for grazing. High grazing pressure leads to increased species richness in nutrient-rich ecosystems, but to decreased species richness in nutrient poor ecosystems. Peak richness is thus expected to shift from low to high nutrient supply depending on grazing pressure. Additionally, higher irradiance may help plants counteract grazing pressure. Thus, the interacting effects of consumers and nutrients on species richness might be stronger at high light intensities. I will perform a field survey of 30 streams that differ in nutrient status, irradiance and grazing pressure to test the predictions about the roles of nutrient status, irradiance and grazing in determining periphyton species richness. This proposal unites the determination of biodiversity, the role of nutrient state in ecosystems, and the relative importance of bottom-up and top-down forces in food-web ecology.
Sweden