Carbohydrate that is consumed during endurance exercise appears to delay fatigue by:

Carbohydrate ingestion during exercise can help to delay fatigue, improve exercise performance by providing a steady supply of glucose that exercising muscles can use, preserve immune function and reduce the rates of muscle breakdown. Carbohydrate consumption during exercise appears to be particularly important during prolonged endurance events lasting 2 or more hours. 

The answer your looking for is a food chain grid. it describes how nature can support itself and survival of the fittest comes into play..