Functional diversity supports the biomass-diversity humped-back relationship in phytoplankton assemblages

Modelling the relationship between biomass and diversity in phytoplankton assemblages provides new insights into the mechanisms responsible for the coexistence of species, even in terrestrial ecosystems.
We tested the biomass–diversity relationship in lake phytoplankton along a wide biomass gradient using functional species groups. We hypothesized that changes in the taxonomic diversity of the phytoplankton along a biomass gradient are associated with altered functional diversity.
For the analyses, in total 768 samples were collected from 30 oxbows, reservoirs and lakes in the Hungarian Lowland Region and analysed between 1992 and 2002.
We found that the diversity and also the number of functional species groups showed a humped-back curve similar to the species richness. The changes in functional group composition act as a good proxy for phytoplankton species responses. We found that the peak of the number of strategy groups and their Shannon diversity was at a much lower biomass tha...