Endemic species are those which are found in just one region & nowhere else in the world. For example Kangaroo to Australia.
Exotic species are the plants which have been introduced into an area outside their normal distribution. For example Acacia and Eucalyptus in India.
Human individuals or even agencies have both intentionally or accidentally introduced these alien species into the ecosystems, sometimes with devastating unintended consequences.
Exotic species may also decrease the species diversity or abundance of the ecosystem.
Invasive species, that are closely related to native species can hybridize with native species and result in the decline or even extinction of the native species.