1. Among the many diversity indices in the ecologist toolbox, measures that can be partitioned into
additive terms are particularly useful as the different components can be related to different ecological processes shaping community structure.
2. In this paper, an additive diversity decomposition is proposed to partition the diversity structure of a given community into three complementary fractions: functional diversity, functional redundancy, and species dominance. These three components sum up to one. Therefore, they can be used to portray the community structure in a ternary diagram.
3. Since the identification of community-level patterns is an essential step to investigate the main
drivers of species co-existence, the ternary diagram of functional diversity can be used to relate
different facets of diversity to community assembly processes more exhaustively than looking only
at one index at a time.
4. The value of the proposed diversity decomposition is demonstrated by the analysis of actual
abundance data on plant assemblages sampled in grazed and ungrazed grasslands in Tuscany (Central Italy).
