To determine the dominant ecosystem types in nonmetropolitan counties and the role of ecological factors in determination of levels of total and age-specific migration patterns within nonmetropolitan areas and ecosystem types for 1950-60 and 1960-70, 30 ecological variables representing POET concepts of population, organization, environment, and technology were used in analyses. Data were classified for the two time periods by age (persons 25-29 and 20-29) and various ecosystem types (for example, small city or suburban manufacturing and trade centers; large, low density mining and manufacturing centers; basic agriculture; rural service centers). Results indicated that a wider range of ecological variables influenced migration patterns over time; effects of ecological factors on migration were significant at both points in time; ecosystem subgrouping increased ability to understand migration patterns; ecological effects were not age specific; variables with direct relationships to total rates showed inverse relationships to age-specific rates; and importance of economic organization indicators decreased while environmental factors increased. Delineation of ecosystems first in examining ecological patterns was supported by the significantly greater percent of variation explained in ecosystems than in the total nonmetropolitan population migration rates, and by variations in types of variables that were significant in different ecosystems. (RS)