Final answer:
Allopatry makes determining species using BSC difficult due to physical separation of populations, while sympatry facilitates easier species identification.
Step-by-step explanation:
Allopatry makes determining species using the Biological Species Concept (BSC) difficult because it involves physical separation of populations. When populations are separated by geographic barriers, such as mountains or bodies of water, they may evolve independently and accumulate genetic differences over time, making it challenging to determine if they are the same species. On the other hand, sympatry, which refers to populations that coexist in the same geographic area, makes it easier to use the BSC for species identification because there is no physical separation hindering gene flow and interbreeding.