Very easy to deduce. A producer in biology of ecosystems is an organism that produces its own food. Another word for a producer in biology is 'autotroph'.
They produce energy directly from the energy given off by the sun or chemicals or both.
Grass (or plants) are producers. They do this with the help of water, converting solar energy into sugar or food, which are usable forms of energy.
So the more grass is consumed, the fewer producers in the area.
