The relationship between species density and community biomass in grazed and ungrazed coastal meadows

Previous studies hair: indicated that the relationship between community bi omass and species density can be represented by a multivariate model in whi ch abiotic variables influence species density both through effects oil bio mass and through effects on the species pool. In this paper, we use data fr om grazed and ungrazed coastal meadows in Finland to evaluate and extend th is general conceptual model of the Factors controlling species density. Str uctural equation analysis was used to evaluate a model for all meadows and then to perform a multigroup analysis to determine how grazed and ungrazed meadows differ. By itself, biomass could explain only 12% of the variation in species density while the multivariate model was able to explain 47% usi ng five types of predictor variables: site, soil, flooding, grazing, and bi omass. Analyses found that flooding explained the greatest amount of variab ility in species density, primarily through negative effects on the species pool. Grazing was also found to have ii strong effect on species density a nd results suggest that its negative influence may be largely through I red uctions in the species pool in grazed meadows. The most important differenc e found between grazed and ungrazed meadows was that species density had a strong negative relationship to biomass in the ungrazed meadows but no sign ificant relationship in the grazed ones. Thus, it appears that the influenc e of competition on species density was much greater in ungrazed meadows co mpared to grazed ones.