Functional diversity of the Australian flora: strong links to species richness and climate

Questions: The taxonomic and functional composition of plant communities captures different dimensions of diversity. Functional diversity (FD) — as calculated from species traits — typically increases with species richness in communities and is expected to be higher in less extreme environments, where a broader range of functional strategies can persist. Further, woody and herbaceous plant families may contribute disproportionately to FD in different bioregions. To build an understanding of these questions using Australia as a case study, we aimed to quantify how FD varies: (a) with species richness, (b) with climate, and (c) between major plant families representing different growth forms. 

Location: Australia. 

Methods: Data on species distribution and functional traits for 14,003 species were combined and FD approximated using hypervolumes (i.e. multidimensional species assemblage trait niche) based on three traits key to understanding plant ecological strategies: leaf size, seed mass and adult height. Plant assemblage hypervolumes were calculated including all species with suitable habitat in each 10 × 10 km grid cell across Australia, and in each of 85 bioregions. Within bioregions FD was also calculated separately for a suite of largely woody and herbaceous plant families. Relationships between FD, species richness and climate were explored. 

Results: As predicted, FD was positively related to species richness and annual precipitation, and negatively related to summer maximum temperature, both in analyses of 10 km × 10 km grid cells and of bioregions (all p < 0.005). However, FD was lowest at intermediate winter minimum temperatures. Patterns identified in families representing different growth forms varied to those observed for all species analysed together. 

Conclusions: Strong links between FD and climate could mean significant shifts in the FD of ecosystems with climate change. Monitoring changes in FD and associated ecosystem functions requires a detailed understanding of FD, which we begin to develop in this study.