How can introduced species threaten native species through hybridization?

Introduced species can threaten native populations through hybridization by interbreeding with species that would not naturally encounter one another. While species are typically genetically isolated, the arrival of an alien species into a new range can break these barriers.1

This process poses a significant risk of extinction, particularly when the native species is rare. In such cases, the native population may be "genetically swamped" by the more abundant introduced species, effectively diluting the native gene pool until the original species is lost.1

A notable example is the white-headed duck in Spain, which faces a threat from the ruddy duck, a North American species introduced to Europe. The ruddy duck hybridizes with the rarer white-headed duck, endangering the latter's genetic integrity. Similar patterns of hybridization-driven decline have been observed globally among various groups, including frogs, fish, wolves, and other birds.1