BIL 330 Lecture Notes - Lecture 30: Herbivore, Stoichiometry
Document Summary
Researchers compiled npp and secondary productivity estimates from terrestrial and aquatic biomes. They found that increases in npp are positively correlated with increases net secondary productivity. The positive correlation suggests an important role of bottom up control in communities. Energy moves through different ecosystems at different rates. Average residence times for primary producers range from more than 20 years in forests to less than 20 days in _______________________. Ecological efficiency: the percentage of net production from one trophic level compared to the next lower trophic level. Ecological efficiency incorporates consumption, assimilation, and net production. Because energy is lost at each of these steps, ecological efficiency is usually low, ranging from 5-20%; 10% is used as a rule of thumb. Low ecological efficiencies make it difficult to have long food chains; there is little energy to support higher trophic levels. Aquatic ecosystems typically have more trophic levels (often five) than terrestrial ecosystems (three to four) due to differences in ecological efficiencies.
