Distributions by ranks of abundance or biomass for organism groups in communities can be described by wide circle of quantitative models, however, existing accuracy of ecological data seldom allows to prefer any of them. Therefore it is offered to apply to the description of rank distributions in ecology the simplest models, containing the least amount of free parameters, or to use models, which grounds contains substantial reasons, additional to acceptable concurrence of model with experimental data.

Much more interestingly, than selection of approximating models, use of rank distributions for indication of ecological condition in communities on the scale “norm-pathology”. It is revealed, that in normal (not disturbed, background etc.) community condition parameters of rank distributions are in quite certain range of meanings, therefore deviations of parameters from meanings from “normal” range can serve criterion and measure of condition pathology. The deviations register stressful influences of abiotic environmental factors on biota. The practice of condition indication by diversity indices, which has taken roots in applied ecology, has the justification that practically all existing diversity indices are unequivocally connected to parameters of different models of rank distributions.