Abstract
The Relative Crowding Coefficient (RCC) is a common measure of interspecific competition in a replacement series experiment. However, the interpretation of RCC depends upon the validity of an assumed functional relationship in total species yield. We develop inference procedures based upon the Relative Yield Total (RY T), a function of species yields in mixture and monoculture plantings, that may be utilized to assess the plausibility of the species yield functional form under which RCC is a reasonable metric of interspecific competition. The performance of the proposed RYT inference procedures is evaluated on the basis of a simulation study. Using the proposed methodology, we conduct RYT inference in a replacement series experiment of bahiagrass ( Paspalum notatum ) and smutgrass (Sporobolus indicus). DOI: http://dx.doi.org/10.4038/sljastats.v5i4.7783
Highlights
Replacement series experiments, first proposed by de Wit (1960), have been used extensively in ecology to assess the relative effects of intra- and intercompetition between two species (McGilchrist and Trenbath (1971); Harper (1977); Berendse (1979); Firbank and Watkinson (1985); for a review of competition indices, see Weigelt and Jolliffe (2003))
Young (Paspalum notatum) and each of two varieties of smutgrass: small smutgrass (Sporobolus indicus) and giant smutgrass, which is known as West Indian dropseed (Sporobolus indicus var. pyramidalis) (Sellers, et al (2011))
Consider a replacement series experiment that is conducted in a greenhouse with one hundred experimental units per planting ratio
Summary
Replacement series experiments, first proposed by de Wit (1960), have been used extensively in ecology to assess the relative effects of intra- and intercompetition between two species (McGilchrist and Trenbath (1971); Harper (1977); Berendse (1979); Firbank and Watkinson (1985); for a review of competition indices, see Weigelt and Jolliffe (2003)). The Relative Crowding Coefficient (RCC) and the Relative Yield Total (RY T ) are common indices of interspecies competition in replacement series experiments If RY T1:1 = 1, RCC1 = 1 only if the relative yield is linear for both species This may be interpreted as identical inter- and intra-species competitive effects. Types III and IV indicate mutualistic or antagonistic interspecific relationships, respectively In such cases the relative crowding coefficient is not a reasonable measure of interspecific competition. Consider the examples of such competition illustrated in the bottom left and bottom right plots of Figure 1.1 In both cases the relative yield functions produce RCC1 ≈ 1, indicative of a lack of interspecific interaction, while in both cases there is a strong interspecific effect.
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