2.6单元 — 迁移对原籍地与目的地的影响

(a) The demographic transition model (DTM) is a generalized model describing how a country's crude birth rate, crude death rate, and total population change over time as the country industrializes and develops economically, typically moving through four or five stages from high birth/death rates to low birth/death rates.

(b) The country is in Stage 2 (Early Transitional). A rapidly falling crude death rate combined with a crude birth rate that remains high produces the wide gap between births and deaths that defines Stage 2.

(c) A Stage 2 country typically experiences very rapid natural population increase (a population explosion), since the birth rate stays high while the death rate keeps dropping; other acceptable answers include a young population structure, declining infant mortality, or continued reliance on an agrarian/rural economy even as health improves.

(d) A Stage 2 population pyramid has a very wide base (reflecting the high birth rate) that narrows quickly moving up through the older age cohorts, giving it a triangular or pyramid shape with a fast rate of taper, since large numbers of children are born but the population above working age remains relatively small.

(e) As a country moves from Stage 2 to Stage 4, the birth rate begins to fall (Stage 3) and eventually converges with the low death rate (Stage 4). This causes the base of the pyramid to narrow and the middle and upper cohorts to fill in and become more even in width, so the shape gradually changes from a wide-based triangle to a more rectangular or column shape reflecting a slower-growing, more evenly distributed age structure.

(f) Malthus argued that population grows geometrically while food/resource production grows only arithmetically, so a country with a high birth rate and falling death rate like the one described would eventually outstrip its ability to feed itself, resulting in famine, disease, or conflict acting as a "check" on population. Modern geographers consider this incomplete because it did not anticipate the Green Revolution and other technological gains in agricultural productivity, nor the fact that many countries voluntarily reduce fertility (moving through Stage 3) as they develop, rather than being checked by catastrophe; Malthus also did not account for global trade allowing food to be moved to where it is needed.

(g) A government could adopt a policy such as expanding access to family planning and contraception, investing in female education, or offering economic incentives to delay marriage/childbearing, any of which tend to lower the crude birth rate and slow the rate of natural increase over time; the response must explain how the specific policy would influence future population growth.

(a) Country Y has the higher rate of natural increase.

(b) Country Y's crude birth rate (34 per 1,000) far exceeds its crude death rate (8 per 1,000), producing a large gap between births and deaths, whereas Country X's birth rate (11) and death rate (9) are nearly equal, giving Country X a much smaller (or near-zero) rate of natural increase.

(c) The epidemiological transition describes the shift in the leading causes of death and illness in a population as it develops, moving from deaths dominated by infectious and parasitic diseases (associated with poor sanitation and malnutrition) toward deaths dominated by degenerative and chronic diseases (such as cardiovascular disease and cancer), which typically accompanies the later stages of the demographic transition.

(d) Country X's leading cause of death (cardiovascular disease and cancer) is characteristic of a later epidemiological transition stage, because chronic/degenerative diseases become the dominant killers only after a country has already controlled most infectious diseases through improved sanitation, nutrition, and medical care, which typically occurs alongside lower death rates and longer life expectancy such as Country X's 81 years.

(e) Country Y's high infant mortality rate (46 per 1,000) is associated with its high total fertility rate (4.7) because in places where a large share of infants and children do not survive to adulthood, families tend to have more children to compensate for the higher expected losses and to ensure enough children survive to support the family and provide old-age security; as infant mortality falls, fertility rates typically fall as well.

(f) Country X's low total fertility rate can be explained by factors such as widespread access to education and career opportunities for women, which raises the opportunity cost of childbearing and delays marriage and first births, and/or the high cost of raising children in an urbanized, developed economy, both of which are associated with later demographic transition stages and reduce the incentive or need for large families.

(g) A country with an age structure like Country X's is likely to face an aging population and a shrinking working-age labor force, which strains pension and healthcare systems as the ratio of retirees to workers rises (a rising dependency ratio); other acceptable answers include labor shortages or increased reliance on immigration to sustain the workforce.

(a) A push factor described in Source 1 is the lack of available farmland in the village (land scarcity/limited economic opportunity in agriculture), which pushes young people to leave.

(b) A pull factor described in Source 1 is the significantly higher factory wages available in the capital city (three to four times what can be earned in the village), which pulls migrants toward the city.

(c) Step migration is a process in which a migrant does not move directly from origin to final destination in one move, but instead relocates in a series of smaller, incremental steps (for example, rural area to a nearby town to a larger city) over time. The pattern in Source 1 can reflect step migration because some villagers first migrate seasonally, testing city life and building resources or connections before committing to a permanent move, rather than relocating permanently in a single, final step from the start.

(d) Source 2 shows that the number of in-migrants declines steadily as the distance from City Z increases: migrants from within 50 miles far outnumber migrants from 50–300 miles, who in turn outnumber migrants from over 300 miles away and international migrants.

(e) This trend illustrates Ravenstein's law that most migrants move only a short distance, and that the volume of migration decreases as distance from the destination increases (distance decay). Because moving is costly and requires overcoming logistical, informational, and social ties to the point of origin, short-distance moves are far more common than long-distance ones, which matches the sharp drop-off in migrant numbers from the nearest to the farthest distance bands in the table.

(f) International migrants face greater barriers such as visa and immigration law requirements, language and cultural differences, the greater financial cost of long-distance travel and relocation, and the loss of established social networks, all of which raise the cost and difficulty of moving compared to a short move within the same region where such barriers are largely absent.

(g) The seasonal return movement is an example of circular (or seasonal) migration, in which migrants move temporarily to a destination and later return to their origin, often repeating the cycle; the permanent relocation described later in Source 1 is an example of permanent migration, in which the migrant intends to stay at the destination indefinitely and does not plan to return to the origin. The key difference is the migrant's intended duration of stay and whether a return move is planned.