When the birth rate is equal to the average fertility required for each female (egg-producing parent) to produce exactly enough offspring to replace herself and her offspring's sperm-producing parent, and the birth rate is sustained for a generation, then ________.

Question

BlackTom AI · Accepted Answer

The question describes a demographic scenario where the birth rate equals the replacement level for each female, and this rate is sustained for a generation. Now, let's evaluate each option in turn to see which characterizes that situation.

Option a: "0 < r < 1". This range implies a positive intrinsic rate of increase that is less than 1, meaning the population would be growing, but not explosively. Since the scenario specifies replacement-level fertility—births just offset deaths—there is no net growth, so this option describes growth rather than stagnation. It does not fit the replacement-level context.

Option b: "r = 0 and there is zero population growth". An intrinsic rate of increase (r) of zero indicates that births exactly balance deaths on average, yielding no net population increase or decrease over time. When this condition is maintained across a generation, the population size remains constant, which aligns precisely with replacement-level fertility.

Option c: "r = 1". An r value of 1 would indicate a population that increases by a factor of 2 each generation if interpreted in some models, or otherwise represents a growth rate unit that is not standard for simple continuous growth models. This would imply net growth, contradicting the replacement-level idea where births offset deaths exactly.

Option d: "population size is at carrying capacity". Carrying capacity refers to the maximum number the environment can sustain indefinitely given resources, space, and other constraints. Replacement-level fertility does not automatically imply the population sits at carrying capacity; it could be, but the defining feature is zero growth, not a state of resource-limited equilibrium. The statement conflates two concepts and is not the direct definition of replacement-level fertility.

Option e: "r > 1". An r value greater than 1 indicates a growing population, which contradicts the scenario of replacement-level fertility where births equal deaths and the population remains stable. This would describe above-replacement fertility or other growth-enhancing factors, which is not consistent with the given condition.

In summary, among the options, the statements that describe zero population growth under replacement-level fertility are those that reflect an equilibrium where births balance deaths, yielding no net change in population size. The other choices imply varying degrees of growth or misinterpretation of what replacement-level fertility entails, making them inconsistent with the scenario.

When the birth rate is equal to the average fertility required for each female (egg-producing parent) to produce exactly enough offspring to replace herself and her offspring's sperm-producing parent, and the birth rate is sustained for a generation, then ________.单项选择题

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