Fox Cable Networks and the National Geographic Channel announced Thursday that they would start a new program service that would focus on natural history and wildlife.

The service, a spinoff of the National Geographic Channel, will appear on the channel that currently is the home of the Fox Reality Channel. Fox announced Wednesday that the reality channel would stop showing its program slate as of March 31.

Called Nat Geo Wild, the new service, which will be a joint venture between Fox Cable Networks and National Geographic Ventures, will concentrate on programs about animals in the wild. It is an extension of a network that has already found success internationally, with outlets in about 50 countries, including England, France and Germany.

Steven Schiffman, the general manager and executive vice president of the National Geographic Channel, said in a telephone interview that the new channel was an ideal “extension of the legacy of the brand.”