ARCHITECTURAL AND LIFE-HISTORY CONSTRAINTS TO SUBMERSED MACROPHYTE COMMUNITY STRUCTURE - A SIMULATION STUDY

We examine here the importance of architectural constraints, together with related life history characteristics, for the variability in submersed macrophyte communities along the gradient of productivity found within a lake's littoral zone. A rule-based simulation model, based on the architectural and life history characteristics of the most important species of Lake Memphremagog (Quebec-Vermont), successfully predicted the species dominance and absence at each site, and the species rank at each site. Use of the model to simulate the community response to environmental changes indicated that increased productivity should involve a change from small rosette species (e.g. Vallisneria americana Michaux) in unproductive communities, to tall species with low biomass density (e.g. Potamogeton crispus L., Myriophyllum spicatum L.) in moderately productive communities, and tall species with high biomass densities (e.g. Elodea canadensis Michaux) in productive communities. The model also predicts that drastic changes in community structure can be brought about under a stable environment by the introduction of alien species with architectural characteristics different from those of the native species.