Assertion: mallard | /r/HasProperty | separated by habitat preference
Facets:
value: formerly
type: TEMPORAL
Source sentences:
text: It has been proposed that the American black duck and the mallard were formerly separated by habitat preference, with the American black duck's dark plumage giving it a selective advantage in shaded forest pools in eastern North America, and the mallard's lighter plumage giving it an advantage in the brighter, more open prairie and plains lakes.