Ecology Indigenous peoples 59 Human ecology 40 History 37 Philosophy 35 Environmental conditions 34 Nature 29 more ... Conservation 25 Environmental policy 25 Environmental protection 23 Natural history 23 Research 23 Effect of human beings on 22 Environmental aspects 22 Biotic communities 21 Birds 21 Climatic changes 19 Economic aspects 18 Mathematical models 18 Religious aspects 18 Social conditions 17 Behavior 15 Evolution 15 Philosophy of nature 15 Biodiversity 14 Forest ecology 14 Pollution 14 Biology 13 Conservation of natural resources 13 Insects 13 less ...