Question

Humpback whales are currently endangered because whaling practices greatly reduced their numbers during the 20th century. Eventually most whaling was stopped by an international agreement in order to keep these whales from becoming extinct.

Critique and decide how could a small population size lead to the extinction of humpback whales?

Responses

A small whale population may adapt to many ecological niches and be unable to settle in permanent marine habitat.
A small whale population may adapt to many ecological niches and be unable to settle in permanent marine habitat.

A small whale population may not consume enough krill and plankton to keep these organisms in check in the ecosystem.
A small whale population may not consume enough krill and plankton to keep these organisms in check in the ecosystem.

A small whale population may be likely to inherit mutations that would make them more fit for survival in a marine ecosystem.
A small whale population may be likely to inherit mutations that would make them more fit for survival in a marine ecosystem.

A small whale population may not be able to reproduce properly and can be easily wiped out by disease and predation.
A small whale population may not be able to reproduce properly and can be easily wiped out by disease and predation.
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Answer 1

Short answer: The only correct response is the last one — small populations are vulnerable to reproductive failure, disease, predation and random events. The other three are incorrect or misleading.

Critique of each statement
- "A small whale population may adapt to many ecological niches and be unable to settle in permanent marine habitat." — Incorrect and nonsensical here. Small populations are less likely to adapt to many niches; humpbacks are already marine and this statement doesn’t describe a mechanism leading to extinction.
- "A small whale population may not consume enough krill and plankton to keep these organisms in check in the ecosystem." — Incorrect as a cause of whale extinction. Low predation on prey might change ecosystem dynamics, but it does not directly cause whales to go extinct.
- "A small whale population may be likely to inherit mutations that would make them more fit for survival in a marine ecosystem." — Incorrect in direction. Small populations are less likely to produce beneficial adaptive changes; genetic drift and inbreeding are more likely to fix harmful mutations or lose variation, reducing adaptability.
- "A small whale population may not be able to reproduce properly and can be easily wiped out by disease and predation." — Correct. Small population size increases extinction risk through:
- Allee effects (difficulty finding mates, reduced reproductive success as numbers fall)
- Inbreeding depression and loss of genetic variation (reduced fitness, less ability to adapt)
- Genetic drift fixing harmful alleles
- Demographic and environmental stochasticity (random fluctuations in births, deaths, or catastrophic events)
- Increased vulnerability to disease, predation, and human impacts

Conclusion: The fourth statement correctly describes how small population size can lead to extinction; the others do not.