Q.33 A species of fish living in a lake are separated by drying up of the lake into two
separate lakes. After several hundreds of years of separation, the two groups are
unable to mate. These groups are now considered to be different_______.
(A) communities
(B) organisms
(C) populations
(D) species
This scenario describes allopatric speciation, where geographic isolation leads to reproductive isolation over time, defining new species under the biological species concept.
Option Analysis
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(A) communities: A community consists of interacting populations of different species in the same area; here, the groups are from one original species, so they do not form separate communities.
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(B) organisms: An organism refers to a single living individual; the question involves groups of fish, not individuals.
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(C) populations: Populations are groups of the same species in one area that can interbreed; these groups cannot mate, so they exceed population status.
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(D) species: Species are reproductively isolated groups; inability to mate after separation confirms speciation.
When a lake dries up and separates fish into isolated groups unable to mate after years, it exemplifies fish lake drying up speciation through allopatric processes. This key evolutionary mechanism is vital for CSIR NET life sciences preparation.
Allopatric Speciation Mechanism
Geographic barriers like drying lakes prevent gene flow, allowing genetic drift and natural selection to diverge populations. Over hundreds of years, mutations accumulate, leading to reproductive isolation where fish from separate lakes cannot produce viable offspring.
This matches the biological species concept: groups reproductively isolated from others. Real examples include cichlids in African lakes.
Why Not Other Options?
Communities involve multiple species interacting, not one diverging. Organisms are individuals, populations can interbreed—these groups cannot, confirming species status.
| Term | Definition | Applies Here? |
|---|---|---|
| Community | Multiple species interactions | No |
| Organism | Single living entity | No |
| Population | Same species, interbreeding | No |
| Species | Reproductive isolation | Yes |
CSIR NET Relevance
Such MCQs test species concepts and evolution; focus on reproductive barriers for scoring. Practice similar questions on isolation mechanisms.
