Ecological Archives E095-143-A3

Susan C. Cook-Patton, Anurag A. Agrawal. 2014. Exotic plants contribute positively to biodiversity functions but reduce native seed production and arthropod richness. Ecology 95:1642–1650. http://dx.doi.org/10.1890/13-0782.1

Appendix C. Partitioning of plant biomass into complementarity and selection.

We made a few modifications to the additive partitioning method of biomass into complementarity and selection effects (Loreau and Hector 2001) to account for contamination of Dipsacus sativus seeds with Dipsacus laciniatus. We used mean biomass of a single plant in monoculture for each species to calculate expected yields instead of the total biomass of an entire monoculture (Cook-Patton et al. 2011). This result produces mathematically equivalent results to the traditional method when the expected relative yield of a species in polyculture (i.e., RYEi) is set to one; in other words, it is expected to be identical to that of a single individual in monoculture. The additive partitioning method is outlined below with our modifications in bold. This method allowed us to use the mean biomass of Dipsacus sativus individuals in monoculture to predict D. sativus performance in polyculture and conversely the mean biomass of D. laciniatus individuals from monoculture to predict D. laciniatus performance in polyculture. We also replaced zero values with a marginal non-zero value (0.001 g) to facilitate calculations (Parker et al. 2010). Finally, we set the expected yield of A. syriaca in polycultures equal to the observed yield to remove the contribution of A. syriaca to the calculations.

 

table

Complementarity is calculated as NΔRYiMi, and selection is calculated as Ncov(ΔRYi ,Mi), The sum of these terms equals the overall difference between the actual yield in polycultures and the expected yield (i.e., YO - YE).

Literature cited

Cook-Patton, S. C., S. H. McArt, A. L. Parachnowitsch, J. S. Thaler, and A. A. Agrawal. 2011. A direct comparison of the consequences of plant genotypic and species diversity on communities and ecosystem function. Ecology 92:915–923.

Loreau, M., and A. Hector. 2001. Partitioning selection and complementarity in biodiversity experiments. Nature 412:72–76.

Parker, J. D., J. Salminen, and A. A. Agrawal. 2010. Herbivory enhances positive effects of plant genotypic diversity. Ecology Letters 13:553–563.


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