LAUSR

Species diversity, functional diversity, species richness, and dominance are fundamental topics in conservation ecology, but studies on their interrelationship remain underexplored and controversial issues in the literature. This investigation is a critical analysis focusing on the interrelations between species taxonomic diversity (based on the Shannon diversity index), cell size-based functional diversity (as a measure of Rao’sQ), species richness (number of species), and species dominance (as per McNaughton’s dominance index) in marine phytoplankton communities. The results revealed no statistical relationship between Shannon’s and Rao’sQ diversity indices, as well as no correlation between these indices and species richness. The importance of the applied functional diversity metric (Rao’sQ) for data interpretation and the misuse of species richness as a species diversity surrogate in the literature were discussed. The taxonomic composition and cell size of the dominant species and the dominant index over time were described. The species dominance index was related to Shannon’s species diversity and Rao’sQ functional diversity according to a negative linear regression, and the inverse correlation between these properties was statistically significant suggesting the species dominance control over the examined diversity system. Patterns across the data sets of species dominance and total community cell abundance showed resembling temporal fluctuations over a 2-year period, implying that species dominance may be a critical driver affecting temporal variations in total community cell abundance. This work provides a comprehensive critical evaluation of the link between taxonomic and functional diversity, and information on the importance of phytoplankton species dominance in maintaining ecosystem functioning.