An interesting argument, but not entirely accurate.
You ask "How long does it take for a "foreign" or "invasive" species to
become a native one?"

Foreign does not equal invasive by the most widely accepted definition.  The
first definition expresses the phrase in terms of non-indigenous species
(e.g. plants or animals) that adversely affect the habitats they invade
economically, environmentally or ecologically.
http://en.wikipedia.org/wiki/Invasive_species  The key to defining invasive
is not whether it's native or non-native but whether it out-competes native
species.

You go on to ask " we argue, using the same logic, that all Whites, Blacks,
and Yellows in America now "non-natives" or "invasive" species?"  

We are all homo sapiens (species), your color breakdown would be ethnicity
or culture.  Using the definition of invasive species, it could be argued
that humans are an invasive species, but not that one ethnic group is more
or less invasive than another.

Anita

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