Any analysis for the detection of a non-random distribution of organisms (e.g. nearest-neighbour analysis or classification techniques). However, the term is applied more particularly to the detection of patterns in the distribution of individuals of a given plant species in a community, by comparing the observed number of individuals per quadrat with the expected number derived from the Poisson series (based on a population that is dispersed at random). The correspondence is tested for statistical significance either by comparing observed numbers with those predicted using the χ2 test, or by comparing the variance : mean ratio for the data with the value for the Poisson series of unity. Where this ratio is significantly greater or less than unity, the population is respectively overdispersed (contagious) or underdispersed (regular). Though first applied to studies of plant ecology, the technique is now widely used in other fields.
Subjects: Plant Sciences and Forestry — Ecology and Conservation.