Complete the passage, using the words and phrases in the box.

nature reserves          habitat loss           ecological balance             food chain               climate change

Earth's habitats are various and many are threatened. Each habitat includes living things, non-living things, and the surrounding environment. The relations of all living things and their environment in a habitat make up the habitat's ecology. (1) _______ or changes in population of plants and animals can cause changes to the natural (2) _______ and the ecology. That means to maintain a(n) (3) _______, we shouldn't cause changes to the climate and the plants and animals of any habitat. In many countries, people have built (4) _______ to keep endangered plants and animals safe. People should also avoid activities that may cause pollution and (5) _______.