Final answer:
The main criterion for identifying species based on the BSC is reproductive isolation, which implies that a species is a group of interbreeding natural populations isolated from others. In conservation, species are chosen for protection based on irreplaceability and vulnerability, reflecting their population status and conservation needs.
Step-by-step explanation:
The main criterion for identifying species based on the Biological Species Concept (BSC) is reproductive isolation. This means that a species is defined as a group of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups. Under the BSC, the occurrence of interbreeding and the shared gene pool are essential for a population to be considered a single species.
In the context of conservation biology and identifying key biodiversity areas (KBAs), species are often selected based on irreplaceability and vulnerability. Irreplaceability is informed by factors like the proportion of a global population present at a site, while vulnerability aligns with the IUCN Red List to identify threshold populations of threatened species. This approach helps in the delineation of areas crucial for biodiversity conservation, which are essential in maintaining the rich tapestry of life on Earth.