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Energy Flow Through Ecosystems

Energy Flow Through Ecosystems. The ultimate source of energy for biological processes is the sun. In other words, the basis of living systems is the solar energy captured through the light-dependent reaction of photosynthesis.

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Energy Flow Through Ecosystems

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  1. Energy Flow Through Ecosystems • The ultimate source of energy for biological processes is the sun. • In other words, the basis of living systems is the solar energy captured through the light-dependent reaction of photosynthesis. • The use of energy to manufacture living material is called productivity.

  2. Productivity Definitions • Primary productivity- the rate at which energy is bound by photosynthesis. It is often measured in kcal/m2/year. • Gross production- the amount of production before metabolic costs (the energy required to sustain life) are subtracted. • Net production- the amount of production after metabolic costs (respiration) are subtracted. • Biomass- the amount of living material present at a given time. It is measured in g/ m2.

  3. Trophic Levels • Energy captured by plants is passed along to other organisms as plants are consumed by them. These organisms are in turn consumed by other organisms. • Food chain- the steps in this transfer of energy. • Trophic level- each step in this transfer. • Primary producers (autotrophs)- the organisms that form the base of the food chain. They include photosynthetic organisms and organisms that derive energy from chemical compounds (chemoautotrophs). • Primary consumers- organisms that eat primary producers. All organisms that eat other organisms are heterotrophs. • Secondary consumers- organisms that eat primary consumers. • Tertiary consumers (top carnivores)- organisms that eat primary and secondary consumers. • Decomposers- organisms that break down the remains of other organisms.

  4. Trophic Efficiency • In nature, food chains interconnect to form food webs. For example, more than one kind of animal may eat the same plant. • Only about 1% of solar energy is captured by living organisms. • From 30-75% of gross primary production is used in metabolic activities. • Due to such metabolic costs, only about 10% of the energy at one trophic level is incorporated into net production at the next level. • When the activities of decomposers (bacteria and fungi) are taken into account, trophic efficiency is much greater than 10%, however.

  5. The Energy Pyramid • If a figure is constructed of the amount of energy at each trophic level, the figure appears as a pyramid. This is due to the metabolic losses in energy that occur at each level. • Primary producers form the wide base of the pyramid, primary consumers form the next layer, and secondary and tertiary consumers form the apex of the pyramid. • Not only energy, but also numbers of individuals in the trophic levels tend to follow a pyramid shape.

  6. Measuring Primary Productivity • Measuring production involves harvesting and weighing biomass produced/ unit time. In the case of plants, underground portions must be considered in measures of productivity. • Factors that influence primary productivity include temperature, intensity of sunlight (which varies seasonally), and the age of the community. • As communities such as forests age, productivity may increase at first, but as they reach old age productivity may decline.

  7. Comparisons of Community Production

  8. Generalizations about Community Productivity • The tropics have among the most productive systems, in part because incident solar radiation is greater toward the equator. • The most productive temperate systems are marshes. Nutrients are continually brought in and wastes are flushed out as water moves through them. • Deserts and oceans are among the least productive systems. Little water in deserts and few nutrients in open oceans are responsible. Thus, 80% of the Earth’s surface is covered by the least productive systems.

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