Living on the edge: Functional trait differences between common and rare species in North Carolina’s Sandhills

Background/Question/Methods           

Conservation of threatened and endangered species (TES) has necessarily focused on individual species. These efforts produce case studies that improve our understanding of focal species, but fail to take advantage of the wealth of information contained in the ecological similarities between species and so have limited generality. In community ecology, trait-based approaches that classify species in terms of their functional traits have become an effective tool for predicting the abundance and distribution of species across environmental gradients in a variety of systems. Trait-based approaches do not rely on species identity, allowing their results to be applied to communities with disparate species pools. Given their success, it is reasonable to extend trait-based concepts to conservation ecology as well. However, there is a conspicuous lack of explicitly trait-based studies in the conservation literature, and little is know about functional traits of TES and how they compare to those of more common species. We measured a suite of 10 important functional traits for 4 TES and 61 common understory plant species from North Carolina’s Sandhills region and examined their distribution to determine whether there are significant functional differences that may explain species rarity.

Results/Conclusions

We show that rare taxa from North Carolina’s Sandhills region have functional trait profiles that are distinct from those of ubiquitous, co-occurring species (Hotelling T² test, p=0.02). Analysis of multidimensional trait space shows that the rare species are restricted to about 1% of the trait space occupied by common species and are an average of 32% farther from the community centroid than common species. The fact that rare species traits are on the fringe of the trait space occupied by the community may indicate a functional basis for their rarity, e.g. that their particular suites of traits are no longer as compatible with the environment at these sites, or are less competitively advantageous than the traits of the more common species. These results have the potential to enhance the effectiveness of conservation efforts by providing managers with objective criteria for choosing species to target with conservation resources.