Rare species loss alters ecosystem function - invasion resistance

The imminent decline in species diversity coupled with increasing exotic sp ecies introductions has provoked investigation into the role of resident di versity in community resistance to exotic species colonization. Here we pre sent the results of a field study using an experimental method in which div ersity was altered by removal of less abundant species and the resulting di sturbance was controlled for by removal of an equivalent amount of biomass of the most common species from paired plots. Following these manipulations , the exotic grass, Lolium temulentum, was introduced. We found that exotic species establishment was higher in plots in which diversity was successfu lly reduced by removal treatments and was inversely related to imposed spec ies richness. These results demonstrate that less common species can signif icantly influence invasion events and highlight the potential role of less common species in the maintenance of ecosystem function.