|MadSci Network: Microbiology|
That is a very perceptive question and it has a complex answer. The relatioship between a microorganism and its enviornment is the product of many factors, all of which must be met if the organism is to thrive. The environment in the human digestive tract is very very different from that in a ruminant (cud chewing) animal like a cow, deer, goat, or bison, but all of the stomach environments in ruminants allow cellulolytic organisms to survive and thrive. For example the human stomach has a very acidic environment that kills many microorganisms. In contast, the rumin stomach (or set of four stomachs) doesn't use the strong acid of our stomach to aid in their digestion. Instesd they use a combination of grinding action (cud chewing) and favorable chemical reactions to provide a comfortable living space for their microbial inhabitants.
I hope this helps you some.
J. R. D. McCormick
Try the links in the MadSci Library for more information on Microbiology.