Natural history Animals 43 Ecology 31 Habitat (Ecology) 14 Biodiversity 13 Biotic communities 13 Physical geography 11 Marine animals 8 History 7 Indians of North America 7 Description and travel 6 Motion picture authorship 6 Earth sciences 5 Weather 5 Deserts 4 Grasslands 4 Jungles 4 Marine ecology 4 Climatic changes 3 Desert ecology 3 Discovery and exploration 3 Endangered ecosystems 3 Human ecology 3 Mountains 3 Volcanoes 3 Animals and civilization 2 Caves 2 Cities and towns 2 Forests and forestry 2 Islands 2