SPECIES LOSS AND ECOSYSTEM FUNCTIONING - EFFECTS OF SPECIES IDENTITY AND COMMUNITY COMPOSITION

Losing a single species from an ecosystem may have large effects on co mmunity and ecosystem properties, but this may depend on characteristi cs of the species and the ecosystem. We examined the effect of losing a single species on productivity and nitrogen retention in experimenta l grassland communities, concentrating on how these effects varied wit h the functional identity of the species lost and the diversity and co mposition of the community from which it was lost. In one experiment, we constructed random plant assemblages that varied in species richnes s to measure the effect of diversity alone on productivity and nitroge n retention. In another experiment, we constructed plant assemblages t o assess the effects of deleting an individual plant species from asse mblages differing in their functional and species richness and composi tion. On average, as species richness declined, productivity decreased but nitrogen retention was unaffected. However, the magnitude and dir ection of change in ecosystem functioning with declining diversity dep ended on the identity of the species deleted and the composition of th e community from which it was deleted. The functional identity of a sp ecies predicted the type of impact its loss had on productivity, but n ot on nitrogen retention.