Productivity of the Ecosystem Teacher Notes PDF

Productivity of the Ecosystem A. The productivity of the ecosystem can be measured in two ways: 1. Gross primary productivity 2. Net primary productivity B. Gross primary productivity: 1. Gross primary productivity is the rate at which the producers (autotrophs) in an e...

Productivity of the Ecosystem A. The productivity of the ecosystem can be measured in two ways: 1. Gross primary productivity 2. Net primary productivity B. Gross primary productivity: 1. Gross primary productivity is the rate at which the producers (autotrophs) in an ecosystem capture energy. 2. Gross primary productivity is the amount of light energy that is converted to chemical energy by photosynthesis per unit time. 3. The photosynthetic organisms in the ecosystem capture the energy from the sun and store it in molecules of glucose. C. What does the plant do with the glucose it produces? 1. About half of the glucose is used immediately in cellular respiration. Respiration is the conversion of glucose into molecules of ATP, the energy source for a cell. 2. Some of the glucose molecules are used as raw materials (building blocks) for the building of other organic compounds within the cell. 3. Much of the glucose is stored by the plant for future use. D. Biomass is a term that is used to describe the amount of organic material in an ecosystem. Producers add biomass to an ecosystem by making organic compounds. E. Net primary productivity 1. The energy stored as biomass is available to other organisms in the ecosystem. 2. Net primary productivity is equal to gross primary productivity minus the amount of energy used by the producers for respiration. 3. Remember: Gross primary productivity is the total amount of glucose produced by photosynthesis. Some of this glucose is used immediately by the plant in cellular respiration. The remaining glucose is stored and is available to consumers. 4. Net primary productivity is the most important measurement because it represents the amount of chemical energy (glucose) that will be available to consumers in the ecosystem. 5. Net primary productivity varies greatly from one ecosystem to another. For example, net primary productivity in a tropical rain forest is about 25 times greater than the net primary productivity in a desert of the same size. 6. Rain forests account for 5% of the Earth’s surface, but account for 30% of the world’s net primary productivity. 7. In terrestrial ecosystems, three factors determine the net primary productivity: a) light b) temperature c) amount of rainfall  An increase in these three factors generally leads to an increase in the amount of photosynthesis taking place, and therefore, an increase in productivity. 8. In aquatic ecosystems, productivity is limited by two factors: a) light b) the availability of nutrients. F. Energy Transfer Between Trophic Levels 1. The amount of energy or matter in an ecosystem can be represented by an ecological pyramid. 2. Ecological pyramid: A diagram that shows the relative amounts of energy or matter contained within each trophic level in a food chain or a food web. 3. Roughly 10% of the total energy consumed in one trophic level is passed to the organisms in the next trophic level. 4. The pyramid shape of the diagram below represents the low percentage of energy transfer from one trophic level to the next. Label each section of the ecological or energy pyramid. 5. Why is the transfer of energy to the next trophic level so low? a) Not all of the energy possessed by the organisms at one trophic level will be passed up to the next trophic level. Organisms use much of the energy they consume for their own life processes such as respiration, movement, or reproduction. b) Many organisms at one trophic level will escape being eaten by the predators at the next level. The energy of these “escapees” will not be passed to the organisms at the higher level. c) Even if the organism is eaten by a predator, some of the molecules in its body will be in a form that the consumer cannot break down and use. An example might be the antlers and hooves of an antelope eaten by a lion. d) Any energy consumed from cellular respiration cannot be passed up to the next trophic level. e) Finally, no energy transformation is 100% efficient. At each trophic level some energy will be lost to the environment in the form of heat. 6. Because each trophic level receives only 10% of the energy from the trophic level below, it can support only about one tenth the amount of living tissue. 8. The low rate of energy transfer between trophic levels explains why food chains rarely contain more than a few trophic levels. Organisms occupying the lower trophic levels are usually much more abundant than organisms belonging to the highest level. There are many more grasses, shrubs, and trees than there are herbivores. There are many herbivores (deer, antelope, gazelles) for each carnivore (lion). 9. Higher trophic levels contain less energy, and therefore, they can support fewer Individuals.