Demographic transitions occur at different times and speed across different economies, and age structures consequently differ across regions. Using a solvable four-phase model, we show that economies with a higher pro...Demographic transitions occur at different times and speed across different economies, and age structures consequently differ across regions. Using a solvable four-phase model, we show that economies with a higher proportion of working-age force and a lower dependency ratio tend to have higher savings rates. Because the demographic ＂ center of gravity＂for investment demand falls at a younger point in the age distribution than that of savings supply, countries with a younger age-distribution like those described above generate national savings in excess of domestic investment, resulting in a current account surplus. Numerical simulation supports this hypothesis. But the relative youth or age of a country＇s population reflects temporary demographic trends which change continuously. Therefore, while trade imbalances caused by demographic factors are structural and long-term, they are not permanent, and may be reversed by changes in age structure.展开更多
Genetic structure data of five populations of the Luehea divaricata Mart. ＆ Zucc., forest tree species under development in the Atlantic Forest biome, obtained by microsatellite DNA markers, were used in simulations ...Genetic structure data of five populations of the Luehea divaricata Mart. ＆ Zucc., forest tree species under development in the Atlantic Forest biome, obtained by microsatellite DNA markers, were used in simulations to study their reproductive and ecological pattern. Different selfing and migration rates were tested, using the observed and expected heterozygosity of 0.55 and 0.67, respectively, obtained through the use of microsatellite markers. Closest values were obtained with the use of selfing rates of 0.3 and migration of 0.2. These results suggest the presence of some self-incompatibility system between these species, which reduces, but does not prevent the self-fertilization. The migration rate contributes to a low genetic differentiation between the populations, making the reproductive mode, responsible for the inbreeding observed in the same populations. Authors suggest continuous monitoring of the genetic variability as a guarantee for the persistence of these populations. The study focus on the importance of using computer simulations to investigate ecologic, reproductive and genetic patterns for forestry populations, thus enabling the application of suitable measures for conservation.展开更多
基金This research is supported by： National Social Science Foundation ＂ Study on China＇s imbalanced foreign trade from the perspective of intra-product specialization＂ （10BJY079）.
文摘Demographic transitions occur at different times and speed across different economies, and age structures consequently differ across regions. Using a solvable four-phase model, we show that economies with a higher proportion of working-age force and a lower dependency ratio tend to have higher savings rates. Because the demographic ＂ center of gravity＂for investment demand falls at a younger point in the age distribution than that of savings supply, countries with a younger age-distribution like those described above generate national savings in excess of domestic investment, resulting in a current account surplus. Numerical simulation supports this hypothesis. But the relative youth or age of a country＇s population reflects temporary demographic trends which change continuously. Therefore, while trade imbalances caused by demographic factors are structural and long-term, they are not permanent, and may be reversed by changes in age structure.
文摘Genetic structure data of five populations of the Luehea divaricata Mart. ＆ Zucc., forest tree species under development in the Atlantic Forest biome, obtained by microsatellite DNA markers, were used in simulations to study their reproductive and ecological pattern. Different selfing and migration rates were tested, using the observed and expected heterozygosity of 0.55 and 0.67, respectively, obtained through the use of microsatellite markers. Closest values were obtained with the use of selfing rates of 0.3 and migration of 0.2. These results suggest the presence of some self-incompatibility system between these species, which reduces, but does not prevent the self-fertilization. The migration rate contributes to a low genetic differentiation between the populations, making the reproductive mode, responsible for the inbreeding observed in the same populations. Authors suggest continuous monitoring of the genetic variability as a guarantee for the persistence of these populations. The study focus on the importance of using computer simulations to investigate ecologic, reproductive and genetic patterns for forestry populations, thus enabling the application of suitable measures for conservation.
