Ecology is a branch of biology concerned with the relations between organisms and their environment. Ecologists work to advance ecosystem research and improve knowledge to protect and restore the services of nature. "Ecosystem services" are the many life-sustaining benefits we receive from nature — clean air and water, fertile soil for crop production, pollination and flood control. These ecosystem services are important to our health and well-being, yet they are limited and often taken for granted as being free. (Source: WordNet, EPA / Photo: Flickr)