It's all about the soil food web and the inter-relationships of all the beings therein;

microbes, minerals and mycellium,

bugs and bacteria,

proteins and protozoa...

everything all food for something else in the cycle, all needed.

Please check out the work of Elaine Ingham and her associates:

http://www.soilfoodweb.com/

http://soilfood.pbworks.com