Are non-native species and invasive species synonyms?

I don't think they would be synonymous. Nonnative species can live in a habitat without causing any adverse effects on that habitat, the nonnative species can become invasive if it causes any negative effects on the habitat. An example of a nonnative invasive species would be the python in the Florida swamp land. These hardy snakes are wreaking havoc by eating fish, birds, even alligator eggs and babies! The two Words are often used interchangeably because it is often hard to find nonnative species that do not harm the environment they are introduced to, but it is possible and seen in some fish and bird introductions.