Rare species contribute disproportionately to the functional structure of species assemblages

There is broad consensus that the diversity of functional traits within species assemblages drives several ecological processes. It is also widely recognized that rare species are the first to go extinct following human-induced disturbances. Surprisingly, however, the functional importance of rare species is still poorly understood, particularly in tropical species-rich assemblages where the majority of species are rare and the rate of species extinction can be high. Here we investigated the consequences of local and regional extinctions on the functional structure of species assemblages. We used three extensive datasets (stream fish from the Brazilian Amazon, rainforest trees from French Guiana, and birds from the Australian Wet Tropics) and built an integrative measure of species rarity vs. commonness, combining local abundance, geographic range, and habitat breadth. Using different scenarios of species loss, we found a disproportionate impact of rare species extinction for the three ...