Mechanisms behind positive diversity effects on ecosystem functioning: testing the facilitation and interference...

Area of Science:

• Ecology
• Ecosystem Functioning
• Biodiversity Research

Background:

• The mechanisms driving the positive relationship between species richness and ecosystem functioning remain incompletely understood.
• Previous work indicated a positive effect of aquatic detritivore species richness on leaf litter breakdown rates.

Purpose of the Study:

• To experimentally test the roles of intra-specific interference and inter-specific facilitation in mediating the effects of species richness on ecosystem functioning.
• To elucidate the specific mechanisms by which species interactions influence ecosystem processes.

Main Methods:

• An experiment manipulating the densities of three detritivore species to assess intra-specific interference effects on leaf breakdown rates.
• A sequential introduction and removal experiment of two species to test for inter-specific facilitation in leaf litter breakdown.

Main Results:

• Decreasing detritivore density positively influenced leaf breakdown rates for one species, supporting the interference hypothesis.
• Process rates per unit biomass increased when one species was introduced after another, confirming inter-specific facilitation.
• The observed effects varied across species, indicating that both interference and facilitation contribute to species richness effects.

Conclusions:

• Both intra-specific interference and inter-specific facilitation are significant mechanisms explaining the positive impact of species richness on ecosystem functioning.
• Intra-specific interference, by inhibiting foraging efficiency, may be a general mechanism driving species richness effects.
• Facilitation, if unidirectional or limited to few species, may be species-specific, emphasizing species identity over richness per se.
• Species loss is predicted to negatively affect ecosystem functioning, with greater impacts from the loss of facilitator species.