I agree with taligat's answer, but I can also add that you don't have to have a career in those fields. You can volunteer. When I was an environmental educator/naturalist we trained volunteers to help with school programs and adult programs. We also had volunteers who had an expertise in certain areas and they would give workshops to the public or lead nature hikes on a certain topic such as Owls or Snakes or whatever. I knew a woman who developed a program to show whale documentaries to tourists in Nantucket, MA all summer long...a great volunteer.
I think if you are a naturalist or an environmental educator, you are probably an environmentalist too. It is the love of nature that drives a person to speak for those who can not speak for themselves and work for the environment in other ways than teaching. That is what I believe an environmentalist is...someone who is "working" for the environment. For instance, I spoke at hearings in Florida to stop development in a 40 acre mangrove forest where Manatees care for their young, I have burned prairies in Illinois to maintain a habitat, I have spoken for and fought for local wildlife causes such as the poisoning of the ground squirrels in my area by the city park managers, I write to my congressman often about passing certain bills...ie: to stop the killing of wolves in Alaska. Those are environmentalist activities and anyone can get involved...volunteering. There are clubs one can join and volunteer too such as the Sierra Club, the Nature Conservatory, your local nature center, your local plant rescue group or a local prairie club, etc.
I hope I have added another perspective.
