PARENT SESSION
Oral Session #41: Biodiversity and Ecosystem Function I.
Presiding: J. Callaway
Tuesday, August 6. 1:00 PM to 4:45 PM. Coconino Meeting Room, TCC.

Effects of species richness on ecosystem functioning: underlying mechanisms.

JONSSON, MICAEL^*,1, MALMQVIST, BJORN¹, ¹ Department of Ecology and Environmental Science, Umea, Sweden

ABSTRACT- Some recent studies published on effects of species richness on ecosystem functioning have found positive effects of increased species richness while others have found negative or idiosyncratic effects. Following up a study that yielded a strong, positive effect of increased shredder species richness on leaf breakdown rates in freshwater, we found that both intra-specific competition and inter-specific facilitation could give rise to the increased leaf breakdown rate. Experiments with other functional feeding groups indicated, however, that both inter-specific interference and exploitation competition may lead to negative species richness effects. Thus, we conclude that idiosyncratic effects of changed species richness may be expected if interactions both with positive and negative effects on process rates are present in a system.

KEY WORDS: Species richness, Ecosystem functioning, Mechanisms, Stream invertebrates