Two required parameters
name and id.
Two optional parameters
accessdate and ref

Examples:

{{NatGeo ecoregion|name=Southeastern Indochina Dry Evergreen Forests|id=IM0210}}
produces
World Wildlife Fund (2001). "Southeastern Indochina Dry Evergreen Forests". WildWorld Ecoregion Profile. National Geographic Society. Archived from the original on 2010-03-08.
{{NatGeo ecoregion|id=na0504|name=Atlantic coastal pine barrens|accessdate=2010-12-21}}
produces
World Wildlife Fund (2001). "Atlantic coastal pine barrens". WildWorld Ecoregion Profile. National Geographic Society. Archived from the original on 2010-03-08. Retrieved 2010-12-21.


The ref parameter behaves as the ref parameter in {{citation}}, useful for Harvard citation style.