Abstract <p>One of the most intriguing challenges in wildlife research is to understand the relationship between habitat heterogeneity and biological diversity. The land surface is comprised of ecologically diverse territories. As a result, widely distributed biological species evolve into numerous ecological forms and genetically adapted populations that can become new species under certain conditions. For instance, freshwater fishes living in rivers can develop unique biological characteristics and genetic pools under the pressure of specific environmental factors. One approach to understanding species structure is to “regionalize” its range heterogeneity based on key ecological and biological criteria, and to assess the genetic divergence of populations in different pats of the range. This involves dividing the area into ecogeographic regions based on environmental characteristics and geographic barriers to dispersal (gene flows). Using the Far Eastern catchments as an example, I discuss intraspecific genetic structure, focusing on genetic variation between and within ecogeographic units of reproduction of genetically similar populations (or a single genetically unique population) of a given species. This implies a hierarchical structure of a species’ range, consisting of ecogeographic regions, units and local populations. I demonstrate how ecogeographic units can be genetically identified and validated for the commercially important chum salmon and the endangered Sakhalin taimen as n examples, and discuss the aspects of species management strategies aimed at conserving biodiversity.</p>