Biological Species Concept: Defining Species

The biological species concept is a fundamental idea in evolutionary biology. It defines a species based on its ability to interbreed.

Reproductive Isolation Criterion

The key criterion used to define species under the biological species concept is reproductive isolation. This means that populations are considered different species if they cannot successfully interbreed in nature and produce fertile offspring. Gene flow between populations must be prevented for them to remain distinct species.

Why Other Options Are Incorrect

• Niche partitioning describes how species use resources differently to avoid competition, but it doesn't define species boundaries.
• Morphological divergence refers to physical differences between groups. While often associated with speciation, it's not the primary definition for the biological species concept, which focuses on reproductive compatibility.
• Genetic distance measures the degree of genetic difference between populations. High genetic distance might suggest separate species, but the biological species concept hinges on reproductive isolation, not just genetic divergence.

Therefore, reproductive isolation is the defining characteristic.