PS 7-89 - Plant rarity related to phylogenetic divergence in biomass: Implications for ecosystem function

Abstract: Species rarity is a common phenomena across global ecosystems and is becoming increasingly more common under climate change. While the rarity of species is often thought to be a consequence of environmental constraints, we examined the hypothesis that plant rarity is a consequence of natural selection acting on functional traits that affect a species range size, habitat specificity, and population aggregation; three primary descriptors of rarity. Using a common garden of 25 species of Tasmanian Eucalyptus, we find that the rarest species have 53% lower biomass than common species. There is also a negative phylogenetic autocorrelation underlying the biomass of rare and common species, indicating that traits associated with rarity have diverged within clades as a result of environmental factors to reach different associated optimums and evolutionary strategies. In support of our hypothesis, we found significant positive relationships between species biomass, range size and habitat specificity, but not population aggregation. These results demonstrate repeated convergent evolution of the determinants of rarity across the phylogeny. These results also suggest that if rarity is an evolved condition potentially related to plant productivity, rather than a random outcome of environmental constraints, we may need to revise conservation efforts to consider the impacts and distributions of rare plant species to maintain ecosystem function.