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# Use of a Relative Physiological Performance Value in the Prediction of Performance in Multispecies Mixtures from Monoculture Performance

M. P. Austin
Journal of Ecology
Vol. 70, No. 2 (Jul., 1982), pp. 559-570
DOI: 10.2307/2259923
Stable URL: http://www.jstor.org/stable/2259923
Page Count: 12
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## Abstract

(1) A relative physiological performance value is defined as: RiJ = YiJ/YmJ where YiJ is the shoot dry weight yield of a monoculture of species i at a factor level J and YmJ is the yield for a monoculture of the most productive species, m, at that factor level. (2) The RiJ values are used to determine relative physiological performance curves for species in relation to a nutrient gradient, using data from a published experiment where performance in monoculture and in five- and ten-species mixtures was recorded. (3) A normalized ecological performance value (EiJ) was defined for multispecies mixtures: $E_{\mathrm{iJ}} = \frac{Y'_{\mathrm{iJ}}}{Y'_{\mathrm{mJ}}$ where Y'iJ is the shoot dry weight yield of species i in mixture at factor level J and Y'mJ is the yield of the most productive species in the mixture at that factor level. (4) For a regression equation of the form log EiJ = a + bRiJ the relative physiological performance accounted for a large part of the observed variation in performance in multispecies mixtures. For three different multispecies mixtures, r2 values greater than 0.6 were found at almost all levels. (5) Examination of the residuals from the regressions, particularly for the ten-species mixture, indicates that specific effects associated with particular species at particular positions along the gradient are important. In particular, Holcus lanatus performance was not well predicted due to its exploitation of a niche (horizontal growth over the sides of the pots) not available to erect growing species. (6) Species ecological maxima, i.e. maximum EiJ value, in these multispecies mixtures correspond in position along the gradient with the species maximum values for the relative physiological performance (RiJ) but do not correspond with the physiological optima measured using absolute yield. This contradicts both Ernst's and Ellenberg's views of the relationship between ecological and physiological optima.

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