Biosphere 2 was privately funded ecological research project in which eight people lived sealed in a structure for two years. It was located in Arizona and was tested as a feasible means for space colonization.  It contained over 3,500 plant and animal species and attempted to reproduce five ecosystems: desert, grassland, marsh, ocean, and rain forest. The human inhabitants (four men and four women) were to grow all their food and recycle their wastes, but used some seed stocks as food.

The project faced several challenges. Some included fish dying and clogging filtration systems, unanticipated condensation making the “desert” too wet, population explosions of greenhouse ants and cockroaches, and morning glories overgrowing the “rainforest”, blocking out other plants. Also it was difficult to manipulate the bodies of water to have waves and tidal changes. The harshest problem was the depleting oxygen levels. The project shut down and the biosphere was taken over by Columbia University who used it for environmental research. (Source & Source)