Final answer:
Gene flow is integral to the biological species concept as it implies the potential for interbreeding, which is the core criterion for defining a species in this concept. Reproductive isolation is also critical as it maintains species boundaries by preventing gene flow between different species, which is necessary for speciation to occur.
Step-by-step explanation:
The importance of gene flow to the biological species concept is evident in its role in defining species based on the ability to interbreed. The biological species concept uses the potential for interbreeding among organisms as the main criterion for determining a species. Gene flow, the movement of genetic material due to the migration of individuals or gametes, is crucial because it is through sex and reproduction that this genetic exchange occurs, allowing for the potential interbreeding that defines a species.
However, reproductive isolation, which prevents different species from interbreeding, is essential for the maintenance of species boundaries under the biological species concept. While the ecological species concept emphasizes natural selection in maintaining species integrity, even in the presence of substantial gene flow, the biological species concept relies on reproductive isolation to facilitate divergent evolution and speciation. Indeed, the disruption or continuation of gene flow can lead to gradual or abrupt phenotypic differences, and potentially, speciation.