The species Rattus norvegicus, commonly known as the brown rat or Norway rat, is native to the regions of northern China and Mongolia. Over time, its range expanded significantly due to its adaptability and human activities.

Brown rats are highly adaptable and can thrive in a variety of environmental conditions, although they have a preference for temperate climates. They are often found near human settlements, particularly in urban environments, agricultural areas, and coastal regions. They are highly opportunistic with regards to shelter and food sources, often occupying sewers, basements, warehouses, and farms.

Rattus norvegicus is an omnivorous scavenger notable for its role as a pest in urban environments. It typically occupies a terrestrial ecological niche, but is also an excellent swimmer, allowing it to exploit aquatic or semi-aquatic habitats. Its flexible diet and ability to reproduce rapidly enable it to colonize diverse environments. In its native and expanded ranges, it plays a role in the ecosystem as both a consumer of various substances and prey for larger predators.