Isolated islands tend to have taxa suited for long distance dispersal e.g. birds and bats, but no other mammals, some reptiles and few/no amphibians. Island species may retain the characteristics of their continental ancestors. Endemism is high on islands but not as much diversity. Relictualism occurs when the ancestral species becomes extinct on the mainland yet remain extant on islands. This could be due to less competition, less extreme climates; in this case, the species on the islands can be considered ‘relicts’.