The correct option is B Interaction between producers and consumers
A network of food chains interconnected at various levels (food web) is meant for increasing the stability of an ecosystem by providing an alternative source of food. So the stability of the ecosystem depends on the interaction between producers and consumers.
If the grass is the producer and the number of producers decreases, the herbivores that feed on it - rabbits, insects, and slugs - would have no food. They would starve and die unless they could move to another habitat. All the other animals in the food web would die too because their food supplies would have died out. The populations of the consumers would fall as the population of the producer fell. And this leads to the deterioration of the ecosystem.
If the number of consumers/carnivores increased then the number of herbivores would diminish. This would affect the stability of the ecosystem.
Primary productivity is the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances.