Final answer:
The value for gross productivity of the primary producers is the same as the value for total heat and respiration due to the energy required for organisms' functions like respiration and heat loss. This remaining energy is known as net primary productivity.
Step-by-step explanation:
The value for gross productivity of the primary producers is the same as the value for total heat and respiration (20,810 kcal/m²/yr) because organisms need to use some of this energy for their own functions such as respiration and metabolic heat loss. This concept is referred to as net primary productivity, which is the energy that remains in the primary producers after accounting for respiration and heat loss. In the given example, 13,187 kcal/m²/yr were used for respiration or lost as heat, leaving 7,633 kcal/m²/yr of energy available for use by the primary consumers.