The relationship between Gross Primary Production (GPP), Respiration (R), and Net Primary Production (NPP) is expressed as:
\[
\text{GPP} - \text{R} = \text{NPP}
\]
In this equation:
- GPP represents the total energy captured by producers within an ecosystem.
- R signifies the energy consumed by producers for respiration.
- NPP denotes the energy remaining after respiration, available for growth and other metabolic processes.
Summary:
The accurate representation is (4) GPP - R = NPP.
Final Determination: \[
\boxed{\text{The correct equation is GPP - R = NPP.}}
\]