Why is the rate of assimilation of energy at the herbivore level called secondary productivity?

(N/A) The rate of energy assimilation at the herbivore level is termed secondary productivity because it represents the rate at which consumers (herbivores) synthesize new organic matter (biomass) from the energy obtained by consuming primary producers (autotrophs). Primary productivity is the rate of biomass production by autotrophs,and since herbivores derive their energy from this source to build their own tissues,their production is referred to as secondary.