The simultaneous use of different diversity indices is strongly recommended, since more
approaches supposedly yield more information, moreover, it could provide opportunity to test the
hypothesis that functional diversity is a more efficient tool for ecological monitoring as compared
to taxonomical indices.
A widespread measure of species diversity is the Shannon index (KREBS, 1998), which is based on
the biomass contribution of each species present in a community.
Depending on the nature of the approach chosen, different methods can be used to determine
functional diversity. After selecting the relevant species traits, functional groups can be identified
using cluster analysis (GOWER, 1971, modified by PODANI, 1999). If the relative biomass of each
group is included in the Shannon formula, the resulting index would be suitable for elucidating
changes in phytoplankton community structure and/or function on a temporal scale. However, in
order to make a cross-site analysis, functional diversity should be defined as the sum of all branch
lengths of the dendrogram obtained by the cluster analysis mentioned above (Petchey and Gaston,
2006), which proved to be an appropriate method for comparing different types of lakes (LONGHI
and BEISNER, 2010).
The relationship between phytoplankton diversity (both functional and taxonomical) and the
selected environmental variables can be evaluated with the help of different statistical methods (e.g.
multiple linear regression analysis).