User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-3062343-20111219023622/@comment-1011548-20111219210323

Migration only works if the species can pass geographical barriers in the way. The only creatures realistically capable of making it to the Deserted Island are Quru Sub and Gobul because they can fly and swim respectively. Also, the extremely different climate of the Desert and Tundra compared to the D. Island means they're probably very far apart geographically, so there's an incredibly tiny chance of anything from the Desert or Tundra making it there accidentally, clinging onto a piece of bogwood or something. Finally, any creature with the adaptations needed to survive in the Tundra or Sandy Plains that does find itself on the D. Island is probably going to die quite quickly.