Species diversity promotes the delivery of multiple ecosystem functions (multifunctionality). However, the relative functional importance of rare and common species in driving the biodiversity-multifunctionality relationship remains unknown. We studied the relationship between the diversity of rare and common species (according to their local abundances, and across nine different trophic groups) and multifunctionality indices derived from 14 ecosystem functions on 150 grasslands across a land-use intensity gradient.
The diversity of above- and belowground rare species had opposite effects, with rare aboveground species being associated with high levels of multifunctionality, probably because their effects on different functions did not trade-off against each other. Conversely, common species were only related to average, not high, levels of multifunctionality, and their functional effects declined with land-use intensity. Apart from the community-level effects of diversity, we found significant positive associations between the abundance of individual species and multifunctionality in 6% of the species tested. Species-specific functional effects were best predicted by their response to land-use intensity: species that declined in abundance with land-use intensification were those associated to higher levels of multifunctionality. Our results highlight the importance of rare species for ecosystem multifunctionality and help guiding future conservation priorities.