Do intrinsically dominant and subordinate species exist? A test statistic for field data

We propose a new method to obtain information about processes that structure plant communities. We analysed the relationship between the presence and dominance of species across a range of habitats. A simple regression model was used to describe this relationship for each species. Based on the regression parameters, we distinguished globally dominant species, which dominate in the same proportion of plots within a habitat as in which they occur, locally dominant species, which reach dominance only when present in almost every plot of a habitat, and intrinsically subordinate species, which never attain dominance. We tested this method using a large data set of species occurrences across a range of salt marsh habitats. The relationships between presence and dominance could be described well by the regressions, and showed large differences between the species. Global dominants occurred later in the succession and higher on the elevational gradient than intrinsically subordinate species. Local dominants were characteristic of early successional stages. These patterns are discussed in the light of colonisation-competition and tolerance-competition trade-offs.