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Title: SPECIES ABUNDANCES INFLUENCE THE NET BIODIVERSITY EFFECT IN MIXTURES OF TWO PLANT SPECIES

Author
item Polley, Herbert
item WILSEY, BRIAN - IOWA STATE UNIVERSITY
item Tischler, Charles

Submitted to: Basic and Applied Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2006
Publication Date: 5/7/2007
Citation: Polley, H.W., Wilsey, B.J., Tischler, C.R. 2007. Species abundances influence the net biodiversity effect in mixtures of two plant species. Basic and Applied Ecology 8:209-218.

Interpretive Summary: On much of the landscape, humans are changing the relative abundances of plant species so that some species are becoming very abundant and others are becoming rare. Whether the increasing disparity in species abundances is affecting the capacity of grasslands and other ecosystems to meet human needs is not known. To determine effects of changing species abundances on grasslands, we experimentally varied the proportional contributions of species in each of six species pairs to the total number of plants in small plots. Aboveground biomass produced by species pairs varied with changes in species ratios only in one of the six species combinations studied. For three of the six species pairs, however, species abundances influenced whether the biomass of pairs exceeded the biomass expected in pairs based on the yield of each species when grown alone. Our results indicate that the productivity of grasslands may be sensitive in the short-term to changes in species ratios caused by grazing, fire, or herbicide application.

Technical Abstract: Species abundances usually are not rigorously controlled when testing relationships between plant production and species richness and may be highly dynamic in disturbed or early successional communities. Whether species abundances affect the yield of mixtures relative to the yield expected from species monocultures [the net biodiversity effect (NBE)] may depend on the amount and type of trait variation that is present in the plant community. To test the prediction that variation in species abundances affects the NBE via changes in the complementarity effect, we grew perennial grasses and forbs in field plots in central Texas, USA as equal-density monocultures and two-species mixtures in which species abundances were varied. The NBE varied significantly with species abundances in three of six species pairs because of changes in the complementarity effect. Our results indicate that mixture yields may be sensitive in the short-term to differences in species ratios.