In order to analyze the possible mechanisms of optimization of biodiversity, the two-level hierarchical model was developed and studied. The lower level subsystems are interpreted as the populations and the upper level is considered as the community of one trophic level consisting of these populations. The indexes at the population level (phenotypic diversity) and at the community level (the number of species) were considered as the characteristics of an integrated hierarchical system. The adaptation of biosystems to environmental conditions occurs through the optimization of diversity at the population and community levels during their interaction. The criteria of optimization used in the lower and upper levels correspond to maximal efficiency of resource utilization by biosystems. The results of modeling correspond to a known empirical biodiversity pattern that allows the use of the optimal diversity principle as an additional mechanism of its formation at the population and cenosis levels.