Populations of a species within an area where the death rate within that population exceeds the birth rate are known as ____________ populations.单项选择题
A
extirpated
B
sink
C
source

Question

Populations of a species within an area where the death rate within that population exceeds the birth rate are known as ____________ populations.

BlackTom AI · Accepted Answer

Since the death rate exceeds the birth rate, the population has a negative intrinsic growth rate (r = b − d < 0), so it is a sink population. 1. Relevant knowledge points and concepts - Metapopulation theory divides local populations into “sources” and “sinks.” - Intrinsic growth rate r = b − d, where b is birth rate and d is death rate. r > 0 indicates growth; r < 0 indicates decline. - A sink population cannot sustain itself without immigration; a source population produces excess individuals that can disperse elsewhere. - “Extirpated” means locally extinct (no remaining individuals). 2. Step-by-step reasoning - The phrase “death rate within that population exceeds the birth rate” means b < d. - Compute r = b − d. If b < d, then r < 0 (negative growth). - A population with r < 0 will decline toward extinction unless rescued by incoming migrants from other populations. - That behavior—persistence only via immigration—defines a sink population. 3. Intermediate calculation illustration - Let b = 2 births per 100 individuals per year, d = 5 deaths per 100 individuals per year. - r = b − d = 2 − 5 = −3 per 100 per year (negative). - To remain at steady state, immigration rate (m) must supply +3 per 100 per year; otherwise population declines. 4. Why the correct answer is correct - The defining fact given (death rate exceeds birth rate → negative growth) matches the definition of a sink: a demographically declining local population maintained by immigration. 5. Why the other options are incorrect - Source: incorrect because sources have birth rate > death rate (r > 0) and export individuals, not decline. - Extirpated: incorrect because that means already locally extinct; the question describes current demographic rates (decline), not absence of individuals. 6. Conclusion - Therefore the correct answer is sink, which matches the provided answer.

Populations of a species within an area where the death rate within that population exceeds the birth rate are known as ____________ populations.单项选择题

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