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Unformatted text preview: levels to their food pyramids. Large carnivores are rare because there is so little energy available to them atop the pyramid. Food generation by producers varies greatly between ecosystems. Net primary productivity (NPP) is the rate at which producer biomass is formed. Tropical forests and swamps are the most productive terrestrial ecosystems. Reefs and estuaries are the most productive aquatic ecosystems. All of these productive areas are in danger from human activity.Humans redirect nearly 40% of the net primary productivity and directly or indirectly use nearly 40% of all the land food pyramid. This energy is not available to natural populations....
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- Fall '10