New Zealand's ecology had evolved in near isolation from the rest of the world for 85 million years. At first settlement it was almost devoid of land mammals. The fauna was very susceptible to land predators. Humans burnt the forests, ate the animals and introduced numerous predators and exotic plants to Otago. This came in two great waves around the years 1300 and 1800, although the effects of both introductions would continue for centuries. This was followed by intensive farming and alteration to the rivers and lakes of Otago for water and electricity production.