What do the polar bears, reindeer, and shrubs that live in a single area makeup

They form an ecosystem.

Explanation:

Different organisms that thrive in a single region in combination form an ecosystem. On certain occasions, it is also illustrated as the composite association amongst all the constituents, that is, whether they are non-living or living present within a specific region.  

Within an ecosystem, one can witness a great degree of biodiversity, as all the constituents found within an ecosystem relies heavily upon each other for one thing or another. A healthy balance between all the components that form an ecosystem makes it a sustainable ecosystem.