Thinkers IAS Youtube channel : www.youtube.com/upscgeneralstudies
This PDF study material on Environment and ecology is one of the most reliable source for UPSC IAS preparation. It contains slides from video tutorials in pdf form.
Links : Environment and Ecology videos : https://www.youtube.com/watch?v=VryrEFQeFo8&index=2&list=PL11qqSwe0f6SDbS2gOIxpYdwlqP2LvRtY