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

Examples:

{{WWF ecoregion|name=Southeastern Indochina Dry Evergreen Forests|id=IM0210}}
produces
"Southeastern Indochina Dry Evergreen Forests". Terrestrial Ecoregions. World Wildlife Fund.


{{WWF ecoregion|id=na0504|name=Atlantic coastal pine barrens|accessdate=2010-12-21}}
produces
"Atlantic coastal pine barrens". Terrestrial Ecoregions. World Wildlife Fund. Retrieved 2010-12-21.


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