Although the process of ecological succession is considered important in many communities, there has been a notable lack of experimental studies designed to test predictions of mechanistic models. The purpose of this study is to test for the importance of noninteractive, facilitative and inhibitory models in benthic algal succession in low order streams. Algal species colonizing initially barren clay tiles will be classified as early successional, late successional or successionally indifferent on the basis of their relative abundance on the substrate through time. The relative importance of facilitative, inhibitory and neutral interactions between early and late successional species will be determined by comparing growth rates of species of each successional type under conditions where the density of early or late successional species has been enhanced in the immigration pool. These manipulations will be performed simultaneously in the presence and absence of indigenous invertebrate grazers to assess their importance. Experiments will be performed in continuous- flow streamside channels which will allow for greater control of confounding influences and replication of treatments. The research will be the first to elucidate successional mechanisms by directly measuring effects of changes in the species composition of algal assemblages on species' growth rates and will help clarify future hypotheses regarding the importance of specific habitat parameters and grazing in influencing the rate and outcome of succession.
