Conversion of biomass into stored chemical energy that is associated with .
Note that this conversion from net primary productivity to secondary productivity is never 100% efficient since not only is it difficult to 100% of the chemical energy associated with but consumers themselves possess metabolic needs. That is, just as there is a difference between gross primary productivity and net primary productivity, there is a difference – in terms of energy stored – between that net primary productivity that is consumed and the resulting secondary productivity.
The greater the metabolic needs of consumers then the greater the difference between net primary productivity consumed and secondary productivity. Ecototherms (i.e., "" animals) thus tend to be more efficient in converting primary productivity into secondary productivity than are endotherms (i.e., animals).
Because secondary productivity within a given environment is never as substantial as primary productivity, the potential for primary consumers (i.e., ) to support secondary consumers (first ) is never as great as the ability of primary producers to support primary consumers. Basically:
Gross 1' productivity > net 1' prod. > net 1' prod. consumed > 2' productivity.
See also trophic efficiency as well as pyramid of productivity, , and .