For two populations of organisms to be considered separate biological species, they must be                   . a. reproductively isolated from each other; b. unable to produce living offspring; c. physically very different from each other; d. A and C are correct; e. A, B, and C are correct

Verified step by step guidance

1. Identify the key concept of 'biological species' which is based on the ability of organisms to reproduce and produce viable offspring.
2. Understand that reproductive isolation is a critical factor in defining species, as it prevents gene flow between populations.
3. Analyze the options given: Option (a) mentions reproductive isolation, which aligns with the biological species concept.
4. Consider the implications of options (b) and (c). Option (b) is incorrect as species can be the same yet not produce living offspring due to other factors like sterility in hybrids. Option (c) is incorrect because physical differences alone do not define separate species without reproductive isolation.
5. Conclude that the correct answer must involve reproductive isolation without necessarily including the inability to produce living offspring or physical differences.

Key Concepts

Biological Species Concept

The Biological Species Concept defines a species as a group of organisms that can interbreed and produce viable, fertile offspring under natural conditions. This concept emphasizes reproductive isolation, meaning that members of different species do not mate or produce offspring that can survive and reproduce.

Reproductive Isolation

Reproductive isolation refers to mechanisms that prevent different species from interbreeding. This can occur through prezygotic barriers, such as temporal or behavioral isolation, or postzygotic barriers, like hybrid inviability or sterility. Effective reproductive isolation is crucial for maintaining distinct species.

Morphological Differences

Morphological differences pertain to the physical characteristics that distinguish one species from another. While significant physical differences can indicate separate species, they are not always necessary for species classification. Some species may look similar yet remain reproductively isolated, highlighting the importance of reproductive barriers over mere physical traits.