Question

The Biological Species Concept (BSC) states that ‘species are groups of interbreeding natural populations that are reproductively isolated from other such groups’. Which one or more of the options could pose challenges for defining species using the BSC?

• A. Fertile interspecies hybrids
• B. Extinct fossil species
• C. Barriers to gene flow
• D. Inbreeding depression

Hint:

Always distinguish: physiological limits define the \emph{fundamental niche}; realized niche is reduced by competition, predation, or limited dispersal. Tolerance itself sets X, not the X–Y difference.

Answer 1

The Correct Option is A, B

Step 1: Recall the Biological Species Concept.
The BSC emphasizes \emph{reproductive isolation} as the defining criterion for species. It works well for many sexually reproducing organisms but has limitations in certain cases.

Step 2: Evaluate each option.
(A) \emph{Fertile interspecies hybrids.}
Yes — if two populations can interbreed and produce fertile hybrids (e.g., certain ducks, plants), the reproductive isolation criterion is blurred. This challenges the BSC. (B) \emph{Extinct fossil species.}
Yes — the BSC relies on reproductive isolation, which cannot be tested for fossils. Thus, extinct species are usually defined using morphological (morphospecies) concepts, not the BSC. (C) \emph{Barriers to gene flow.}
Not necessarily a challenge — barriers to gene flow (e.g., rivers, mountains) \emph{create} reproductive isolation, which supports the BSC rather than undermining it. (D) \emph{Inbreeding depression.}
No — inbreeding depression reduces fitness within a population but does not challenge the definition of species boundaries under the BSC.

Step 3: Conclusion.
The main challenges to the BSC are cases where reproductive isolation cannot be applied or is ambiguous, such as fertile hybrids and fossil species. Final Answer:\quad \(\boxed{\text{(A) and (B)}}\)