Analysis of Competition Experiments

Biologists have, for some time, been studying the effect of growing one plant species in close proximity to another. In some cases the yield of a species is increased over its yield in monoculture and in other cases decreased. A species is regarded as a good competitor if its yield generally increases when grown with other species. This paper presents an analysis of an experiment in which p species are compared by growing pure stand and mixtures in pots or plots at equivalent total density of planting. Each species is grown in monoculture and each combination of two grown in equal proportion. It is assumed that only one harvest is made and that each species is competing either for just one nutrient or for the same nutrients with no differentiation being made between competition for differing nutrients. Such an analysis has previously been presented by K. Sakai [1961] and Williams [1962] and, although the analysis is essentially similar to that of Williams, a different parametrisation is used which corresponds more closely to easily defined biological concepts.