What does "The level of primary productivity in an ecosystem sets the energy budget" mean ?

Question

What does "The level of primary productivity in an ecosystem sets the energy budget" mean ?

Answer 1

Primary production is the production of organic compounds from atmospheric or aquatic carbon dioxide, principally through the process of photosynthesis, with chemosynthesis being much less important. All life on earth is directly or indirectly reliant on primary production. The organisms responsible for primary production are known as primary producers or autotrophs, and form the base of the food chain. In terrestrial ecoregions, these are mainly plants, while in aquatic ecoregions algae are primarily responsible. Primary production is distinguished as either net or gross, the former accounting for losses to processes such as cellular respiration, the latter not.

http://en.wikipedia.org/wiki/Primary_pro...

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This deals with ecosystems and the energy flow and the relationships and the energy they produce.