Abstract
Pelagic studies found that consumer P content and growth rate can be affected by food quality and that fast growing species have higher body P content. The proposed project has two parts that are designed to test whether similar mechanisms are at work in benthic ecosystems. The first part will test two key hypotheses about growth rates and nutrient content of snail grazers, by using material from an earlier experiment, where nutrients, light and grazer density were manipulated: (1) Snail growth increases with increasing nutrient levels and shading, and decreases with increasing competition. (2) Snail growth is positively related to snail body P content and to food P content. In the second part, 30 streams, which differ in eutrophication due to differential land use, will be sampled in a nested hieratical design. This stream survey will test two more key hypotheses about the effects of N and P contamination on periphyton nutrient content and consumer species composition, growth rate and P content: (3) Invertebrate community composition changes from slow growing species with low P content to fast growing species with high P content along a gradient of increasing eutrophication. (4) Within species, individual growth rate and P content is lower in pristine than in eutrophic streams. Clarifying the mechanisms regulating invertebrate species composition, growth and stoichiometry will help to predict effects of eutrophication and loss of riparian vegetation on benthic ecosystems.
Sweden