The GAIAS program has several "tracks" that students can choose: People, Politics, and the Environment; Evolution, Ecology, and Conservation; and Marine Ecology. Which classes you will have depends on which track you are in, though there is a possibility to change one or two of them if you need to. An example of the classes offered in each track is available here.
Not all tracks are offered every semester. Offerings depend on the number of students who apply for them each semester. However, the Evolution, Ecology, and Conservation track and People, Politics, and Environment tracks are the most popular choices and are usually available every semester.