Biosphere II is a man-made closed ecological system duplicating earth (Biosphere I) - in Oracle, Arizona, built (1987-89) by, Space Biosphere Ventures and now managed by Environmental Research dept. of Columbia University. The project conducted two sealed missions; first from September 26, 1991 to September 26, 1993 and second for six months in 1994 – Both Failed - why read further... - Did we any Lessons ?? - there is a Calvin & Hobbes cartoon (Copyright of Bill Watterson) that answers this question
Biosphere II project demonstrated how fragile the balance can become. This grand experiment attempted to replicate natural ecosystems inside a self-contained world. However, the system started to fail several months into the experiment. All parts of the ecosystem inside Biosphere II, were in jeopardy because the experiment's designers had overlooked the importance of every parts in an ecosystem, including that of microbes.
The delicate balance of microbes in the soil was tipped when too much fertilizer was used to prepare the soil for crops. The microbial population grew too fast and consumed a huge amount of the oxygen inside the Biosphere. Other species started to die. In desperation, both the team and the external supervisors decided to pump air from outside into the Biosphere. They had failed their primary goal -- all because of their underestimation of the microbes -- one tiny, but crucial part.
To completely understand an ecosystem, (which is beyond human intelligence as per Fukuoka San (One Straw Revolution) - it's necessary to examine every component, including the unseen microscopic life and there relationship with each other and with other lifeforms both living inside /outside the lifeforms. Failure of this experiment was a rude shock to the Biologist who thought they could replicate something like mother earth !...
Somewhere I read...
Ecosystems are like human beings-- working systems composed of living things. Each life form contributes to the whole in multiple ways, providing food for other life forms or consuming others or decomposing. The whole system depends on each member to fulfill a particular job. If something happens to one part, anywhere in the ecosystem, the rest of the ecosystem would suffer. If one species becomes extinct with it several microbes which are dependent on it - and their role we don't yet know. The simple(?) dung beetle role itself is so valuable in Ecology then we can only imagine(?) what are the roles of microbes in the Ecology
Of the 400 odd types of bacteria living in each one of us - we just know a few of them that too partially - we don't have a clue of the inter-relation between these microbes and the billions of microbes outside our body and other organisms /plants and their role in the food we eat and environment... the list is endless.