Question

Which one or more of the following phenomena make(s) small populations vulnerable to extinction?

• A. Inbreeding depression
• B. Demographic stochasticity
• C. Intraguild predation
• D. Continuous population growth

Hint:

Focus on mechanisms that get worse specifically as population size shrinks, not general predator-competitor interactions or population growth.

Answer 1

The Correct Option is A, B

Step 1: Understanding the Question.
Small populations face special extinction risks that large populations mostly avoid. We are asked to identify which of the four listed phenomena are recognised drivers of extinction risk specifically in small populations.

Step 2: Key Concept.
Conservation biology identifies a set of factors that raise extinction risk as population size shrinks: loss of genetic diversity leading to inbreeding depression, and random ups and downs in births, deaths and sex ratio (demographic stochasticity) that can be fatal when there are only a few individuals left to buffer such randomness. Ecological interactions like predation between competing species, or a growing population, are not in themselves markers of small-population vulnerability.

Step 3: Detailed Explanation.
Option (A): Inbreeding depression. In a small population, individuals are more likely to mate with close relatives because there are fewer unrelated partners available. This raises the frequency of harmful recessive alleles being expressed, lowering offspring survival and fertility, and pushing the population further toward extinction. So (A) is correct.
Option (B): Demographic stochasticity. This refers to random chance variation in individual births, deaths, and sex ratios. In a large population these random fluctuations average out, but in a small population, a run of bad luck, such as several deaths or a skewed sex ratio in one generation, can disproportionately shrink or even wipe out the population. So (B) is correct.
Option (C): Intraguild predation. This is predation between species that also compete for the same resources, and while it can affect population sizes generally, it is an ecological interaction that operates regardless of population size, not a phenomenon that specifically makes small populations more vulnerable than large ones. So (C) is not correct in this context.
Option (D): Continuous population growth. A population that keeps growing is moving away from extinction risk, not toward it, since a growing population size directly reduces vulnerability. This is the opposite of a risk factor, so (D) is incorrect.

Step 4: Final Answer.
Inbreeding depression and demographic stochasticity are genuine phenomena that specifically endanger small populations, so options (A) and (B) are correct.
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