HUMAN ECOLOGY: The Microbes In Your Body. “This sort of diversity is made possible thanks in part to the vast number of ecological niches in the human body. Microbes that live on the surface of the skin can get lots of oxygen, but they also bear the brunt of sun, wind, and cold. Microbes in the intestines have next to no oxygen, but they have a much more stable habitat. Microbes have carved up the human body into far finer niches. The bugs on your fingers are different from the ones on your elbow. The two sides of a single tooth have a different diversity of microbes. . . . Here’s one crude but effective example of what this kind of ecosystem engineering might look like. A couple years ago, Alexander Khoruts, a gastroenterologist at the University of Minnesota, found himself in a grim dilemma. He was treating a patient who had developed a runaway infection of Clostridium difficile in her gut. She was having diarrhea every 15 minutes and had lost sixty pounds, but Khoruts couldn’t stop the infection with antibiotics. So he performed a stool transplant, using a small sample from the woman’s husband. Just two days after the transplant, the woman had her first solid bowel movement in six months. She has been healthy ever since.”