The eastern fox squirrel (Sciurus niger) was first introduced to Los Angeles in 1904. Since that time, this species has spread throughout many of the urban and suburban areas of Los Angeles, Ventura and Orange Counties. In this paper we document that the eastern fox squirrel can replace the western gray squirrel within a particular habitat in a short period of time.
Muchlinski, Alan E.; Stewart, Glenn R.; King, Julie L.; and Lewis, Suzanne A.
"Documentation of Replacement of Native Western Gray Squirrels by Introduced Eastern Fox Squirrels,"
Bulletin of the Southern California Academy of Sciences:
Available at: http://scholar.oxy.edu/scas/vol108/iss3/3