Question

Discussion

Why is migration more difficult to measure than fertility and mortality? How do changes in fertility, mortality, and migration affect population composition?

Answer 1

Migration,, mortality and fertility are principal determinants of growth (or its inverse) within the absence of technological intervention, one might say almost the only determinants, but improvements in contraceptive techniques, increasing acceptance of abortion, and slackening of some traditional religious and cultural traditions has in many parts of the earth reduced the role of fertility.
Mortality
The effect of mortality on population structures is to cut back the component of the population during which the mortality occurs. Historically, the foremost dangerous ages were infancy and adulthood (variously reckoned per circumstances). additionally, some epidemics of infectious diseases. Example spanish flue had their highest mortality among young adults, whose immune systems were presumably insufficiently primed. it's expected that the forecast bird flue epidemic will behave similarly. War differentially reduces the proportion of younger men. The majority of infectious diseases of babyhood are reduced by immunisation, and improved nutrition and hygiene have rendered childhood safer. Antibiotics, state, and enhancements in medical, surgical, and palliative care have resulted in great increases in expectancy within the developed world, where expectancy is now within the center to upper 70s or lower 80s, and rising once a year. The effect of this could be to spice up the population within the upper age groups substantially. Women have higher expectancy than men wherever they live.
Migration
This has been less studied. In areas where natural disasters or politico-military concerns end in entire populations being displaced the initial population structure are visiting be unchanged, though post-migration the population will have altered to reflect folks that have survived the tactic, typically showing increases in older children and younger adults. Opportunistic migration tends to occur mostly among younger adults, and will be permanent or temporary. Some of the studies among the migrants shown increased fertility levels, that the effect of migration on population structure is to deplete the population emigrated from within the young adult groups, to strengthen this group within the immigrated-to population, and to increase the fertility/birthrate within the new population.
Increased fertility rates and migration can have remarkable effects on the overall structure of populations.For example within the u. s. the mixture has led to the Hispanic group becoming the foremost important ethnos within the country. The rising of the Hispanic population within the last three or four decades has in effect rejuvenated the aging U.S. population by adding children and working-age adults, at the identical time making it more ethnically diverse. the dimensions of the Latino population doubled between 1980 and 2000, and Latinos also accounted for 40% of the country's growth. That rising has continued since 2000, accounting for nearly half the increase of the U.S. population (U.S. bureau, 2006)