|Wilsey, Brian - IOWA STATE UNIVERSITY|
Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: May 11, 2004
Publication Date: October 29, 2004
Citation: Wilsey, B.J., Polley, H.W. 2004. Realistically low species evenness does not alter grassland species richness-productivity relationships. Ecological Society of America Abstracts. p. 547. Technical Abstract: Biodiversity is declining world-wide from reductions in both species richness and evenness. Field experiments have shown that primary productivity is often reduced when richness of plant species is lowered. However, experiments testing richness effects have used evenness levels that are much higher than normally encountered in plant communities and have been based on the assumption that species extinctions are random. We experimentally varied, for the first time, both species richness (1-8 perennial species per m2) and species evenness (near maximal vs. realistically low) in grassland plots. Net primary productivity and ecosystem CO2 uptake declined when richness was reduced, and reductions were similar between evenness treatments. Richness effects were associated more with a selection effect than with complementarity (found only with high evenness). Importantly, extinctions in plots during the second year were not random but were greater at low than at high evenness (i.e. with increased rarity) and in species with low aboveground growth rates. Our results indicate that richness studies may not be biased by using mixtures with artificially high evenness levels, but also demonstrate that results from these studies are directly applicable only to communities in which plant extinctions are random.