What he found when he arrived was that most of the animal species on the Galapagos live nowhere else in the world, although they resemble species living on the South American mainland. Through Darwin's observations on the Galapagos, the direction of biology has been changed forever. Because of islands limited size and isolation, they provide excellent opportunities for studying some of the factors that affect the species diversity of communities. While this is good for science, this has been devastating for the Galapagos Islands. Islands are such an isolated system that the number of species brought to an island will directly affect the number of animals that become extinct.
Islands reach equilibrium in the plant and animal species richness.
When new species are brought to the islands, the environment becomes very disrupted and forever changed. As time has progressed, groups of people have left their mark on the fragile islands. In the late 1600s, the buccaneers brought rats, cats, goats, burros, horses, and cattle that destroyed the habitat for the tortoises and other animals. They also took with them large numbers of the tortoises for meat. Since 1990, forty tortoises have been killed for their distinctive tasting oil.