Productivity in ecology refers to the rate at which biomass or organic matter is generated in a particular ecosystem. Primary productivity is the rate at which energy is converted by photosynthetic autotrophs to organic substances. Hence, are called primary producers. On the other hand, the process at which these autotrophs are consumed by herbivores is called secondary primary production. Two aspects of primary productivity include gross (GPP) and net primary productivity (NPP). GPP is the rate at which photosynthesis occurs whereas NPP is the total difference between GPP and the energy used by the producers for respiration (R). It is usually expressed as GPP = NPP - R. NPP is correlated with foliar standing crop biomass, as leaves are the main location of photosynthesis. Reduction of foliar standing crop biomass by herbivores therefore causes reduction in NPP.
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