Which term is used to explain a shared gene pool where not all populations can interbreed?

The term that describes a shared gene pool in which not all populations can interbreed is "ring species." In the context of evolution and population biology, ring species illustrate a situation where groups of connected populations exhibit gradual phenotypic differences, and while they can interbreed with neighboring populations, those at the end of the ring may not be able to interbreed with each other. This creates a scenario where there is a continuous gene flow among most populations in the ring, yet significant barriers to reproduction exist between the terminal populations.

This phenomenon is significant in understanding species and the concept of speciation, as it challenges the traditional biological definitions of species that often emphasize reproductive isolation. Ring species show that the boundaries of species are not always clear-cut and that the degree of interbreeding can vary within different segments of a population.

In contrast, the other terms, while related to biological classification, do not adequately capture the nuanced interbreeding dynamics represented by ring species. "Species" typically refers to a group of organisms capable of interbreeding, "community" denotes a group of different species living in the same area, and "subspecies" refers to a taxonomic category that provides a more specific classification within a species, usually indicating populations that have distinct