In the pages about the Galapagos islands, the word «endemic» is often used to describe a species that only occurs on these islands. Endemic animals or plants are restricted to a particular geographic region and found nowhere else in the world. Endemism usually occurs in areas that are isolated in some way. Since the Galapagos were never connected to the mainland which lies 960km away, all species had to reach the islands either by swimming (fish, sea lions etc.), by flying (birds, insects etc.) or on rafts (land animals, mammals, reptiles etc.). Once here they evolved and occupied different ecological niches. The endemic species in the Galapagos are specially adapted to the harsh conditions on the archipelago like the scarcity of fresh water, the availability of only certain food and the dark volcanic rocks.