Summary
Models of interaction between two genotypes are described. The models, known as “replacement series” are based on spacing formulae which were first described by C. T. de Wit. It is assumed that the total number or density of individuals is held constant, but the proportion of the two components of the mixture is varied. The output of each component at the end of a period of growth is determined; this may be dry matter production, seed output or any other relevant parameter.
Four varieties, two linseed (Redwing and Valuta), two flax (Stormont Gossamer and Wiera), were grown at three densities in four varietal combinations, and were harvested after four and one-half month's growth. When total dry weight and seed number were plotted as replacement series graphs, the total yields of the mixtures were frequently greater than would be expected from the growth of pure stands. Thus there was some form of augmentative interaction between varieties which would lead to a stable equilibrium if the mixture was resown in successive years. In most of the varietal mixtures there was strong evidence that relative fitness values were frequency-dependent. Usually the relative fitness of one component decreased as its frequency in the mixture increased. The results showed that frequency-dependent selection occurred between genotypes of flax or linseed due to annidation. It appeared that the patterns of growth and maturity of flax and linseed were different. Flax grew more rapidly and matured earlier than linseed and this difference in timing of growth led to annidation.
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Khan, M., Putwain, P. & Bradshaw, A. Population interrelationships. Heredity 34, 145–163 (1975). https://doi.org/10.1038/hdy.1975.20
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DOI: https://doi.org/10.1038/hdy.1975.20
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