Out of all of the answers given, "Community" fits the definition best and is most similar to the definition of a population. A biome is a naturally occuring community of flora and fauna in a habitat, such as a forest or jungle.
An ecoprovince includes an area of a one climate, such as a mountain range or plateau. A specifics is a group of living organisms that can breed with each other and exchange genes. An ecotone is the boundary between two distinct biomes, such as the line between a flat meadow and a tree-filled forest.