13 3 Energy Flow in Ecosystems

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Primary Productivity of rainfall the system receives since water is a. raw material of photosynthesis In addition, Primary productivity is the amount of light energy. photosynthetic organisms need certain nutrients, that autotrophs in an ecosystem convert to chemical. such as nitrogen potassium and phosphorus to,energy and store in organic compounds during a. grow Even though many of these nutrients are not, specific period of time It is commonly measured in. directly involved in photosynthesis they contribute. terms of energy per area per year J m2 a It can,to limiting the rate of primary productivity by.
also be expressed as biomass mass of vegetation,affecting plant growth. added to an ecosystem per area per year g m2 a It, is important to remember that primary productivity. is the rate at which organisms produce new Energy Transfer at. biomass which is not the same as the total mass of Higher Trophic Levels. all photosynthetic autotrophs present in an area at Not all solar energy captured by primary producers. one time For example a forest has a very large is passed on to higher trophic levels A substantial. biomass the mass of its vegetation is greater portion of the energy captured by producers is used. than that of a grassland of equal size But primary in their own cellular respiration reactions Another. productivity of the grassland may actually be large portion is simply never eaten by consumers. higher because animals are constantly eating the which is why many ecosystems look green. plants and new ones are being produced Thus Only some of the total biomass eaten by. new mass is being accumulated in the grassland at consumers is converted into the body tissues of the. a higher rate than in the forest organism that ate it Figure 13 19 on the following. The amount of primary productivity as shown page shows what happens to the energy a herbivore. in Figure 13 18 can vary significantly both among caterpillar obtains from the plant material it eats. ecosystems and within an ecosystem over time Approximately half the plant tissue is indigestible. The rate of productivity depends on many factors and the energy from this portion is expelled with. including the number of autotrophs present in the the caterpillar s feces Although some of this energy. ecosystem the amount of light and heat present will be consumed by decomposers and will. the process slows during winter and the amount continue to be part of the ecosystem it will not. open ocean 65 0,continental shelf 5 2,extreme desert rock sand or ice 4 7. desert and semi desert scrub 3 5,tropical rain forest 3 3. savanna 2 9,cultivated land 2 7,boreal forest taiga 2 4.
temperate grassland 1 8,woodland and shrubland 1 7. tundra 1 6,tropical seasonal forest 1 5,temperate deciduous forest 1 3. temperate evergreen forest 1 0,swamp and marsh 0 4. land and stream 0 4,estuary 0 3,algal beds and reefs 0 1. upwelling zones 0 1,0 1 2 3 4 5 6 0 0 5 10 15 20 25.
A Percentage of Earth s B Average net primary C Percentage of Earth s. surface area productivity g m2 a net primary productivity. Figure 13 18 Why do the oceans contribute such a high solar energy transformed to chemical energy by autotrophs. proportion of Earth s total primary productivity when their called gross primary productivity minus the amount used. average productivity is low compared with that of algal beds by the autotrophs during cellular respiration. and reefs Net primary productivity is the total amount of. Chapter 13 Ecological Principles MHR 445,be available to the secondary consumers that eat. caterpillars Approximately one third of the energy. the caterpillar obtains is used in its own cellular 100 J feces. respiration providing energy for locomotion,maintaining body temperature and other body. processes and therefore lost to the ecosystem, In fact only about one sixth of the energy is 33 J. plant material eaten respiration,incorporated into new caterpillar tissue tissue. by caterpillar,that can be eaten by secondary consumers.
This energy loss and its related unusable heat, occurs between all trophic levels in a food web see 67 J growth. Figure 13 20 Although the efficiency with which,energy is transferred from one level to the next. Figure 13 19 Why is so much energy lost as waste from a. varies among different types of organisms it,caterpillar. usually ranges between 5 and 20 percent In other,words roughly 80 to 95 percent of the potential. energy available at one trophic level is not The next MiniLab will help you understand. transferred to the next one This pattern of energy pyramids of productivity by examining three. loss is often illustrated as a pyramid of typical food chains. productivity see Figure 13 21 on page 448,heat energy loss to environment.
decomposers 100 energy to environment,loss 23 8 loss 76 2. top carnivores,organic wastes dead tissue,respiratory heat loss. loss 23 5 loss 71,carnivores,herbivores,20 4 loss 63 4. photosynthesis,1 2 solar energy,Figure 13 20 Why is the. respiratory heat loss of,consumers higher than Earth Sun.
that of producers Note,that it is highest for,top level carnivores. 446 MHR Unit 5 Population Dynamics, BIO FACT Since progressively less energy is transferred from. lower to higher levels in a food web less biomass, Meat is more easily digested than most plant materials so. can be produced at the higher trophic levels This, carnivores are slightly more efficient at converting food into. biomass However carnivores typically use up more of this. concept can be represented in a biomass pyramid, biomass during their own cellular respiration because their in which each tier represents the biomass of that.
energy needs are higher than the energy needs of herbivores trophic level see Figure 13 22A on the following. Carnivores tend to move around more to find food and page Typically the shape of a biomass pyramid is. many of them are endothermic similar to that of a pyramid of productivity However. in some aquatic ecosystems a relatively low biomass. of primary producers called phytoplankton,supports a higher biomass of primary consumers. zooplankton as shown in Figure 13 22B This, Where Do You Fit in 2 How might diet influence the number of humans Earth. can ultimately support,the Food Chain, How might your knowledge of pyramids of productivity 3 A square metre of land planted with rice produces. influence your decision about the type of foods you include about 5200 kJ of energy per year A chicken farm. in your diet Recall that only a very small fraction of the produces about 800 kJ m2 of potential food energy. energy released by the Sun is assimilated into plant material per year Assume that a human must consume 2400 kJ. see Figure 13 17 on page 444 For ease of calculation per day to survive Although it is an oversimplification to. assume that the amount of energy captured by plants and imply that a person could survive by eating only one. contained in their tissues is two percent of the total energy type of food calculate the total area of land needed to. available from sunlight Additionally although it is a support the student population of your school for one. simplification assume that 10 percent of the energy at one year on a diet of. trophic level is transferred to the next level Study the a rice b chicken. diagram and determine the percentage of the Sun s energy. 4 Research the differences between the food used to. available to humans as shown at the top of each of the. feed chickens and other poultry in small family run. three food chains, farms and the type of feed used in large commercial. Analyze agribusiness operations Which do you think is more. 1 About 80 percent of the world s population eat mostly environmentally friendly. grain based foods Why do you think this is the case. Sun Eighty percent of humans have a diet mostly of grain. grain humans,2 0 2 but many Canadians like Americans.
Sun and Europeans also consume much,meat and fish,grain beef humans. 2 0 2 0 02 0 002 0 0002, phytoplankton zooplankton copepods herring tuna humans. Three typical food chains for humans with different diets. Chapter 13 Ecological Principles MHR 447,Figure 13 21 This figure is drawn. to show a 10 percent efficiency of,Primary 1000 J energy transfer from one trophic. level to the next Although the rate,of efficiency varies from 5 to.
20 percent 10 percent is a,Primary commonly used average figure. producers This gives rise to what is,sometimes called the rule of 10. when describing the shape of this,1 000 000 J of sunlight. occurs because the phytoplankton are eaten so Animals that make up the highest trophic level. quickly that there is no time for a large population in an ecosystem tend to be large predatory species. to develop The population of zooplankton can such as lions whales hawks and eagles Since. only exist because the phytoplankton have an biomass is limited at the top of the pyramid there. extremely high reproductive rate new organisms can only be a few of these large animals in any. appear as fast as others are eaten This means that ecosystem at one time In fact when you compare. the productivity of phytoplankton is very high and the number of individual organisms at each trophic. the pyramid of productivity for this ecosystem is level you will find that the same pyramidal shape. therefore wide at the top and narrow at the bottom appears The pyramid of numbers in Figure 13 23A. In every ecosystem the biomass of carnivores at shows the effect of the decreasing energy supply on. the highest trophic level is very limited Only a the number of individuals at each level Although. tiny fraction of the chemical energy captured by the supply of solar energy is almost limitless. photosynthesis flows all the way through a food almost all of the energy is eventually lost from. web to a tertiary or higher level consumer Thus ecosystems as a result of inefficient transfers. most food webs are limited to five or fewer trophic between trophic levels. levels there is just not enough energy left to Not all pyramids of numbers have this shape. support more levels In a forest for example a few individual primary. producers trees have enough biomass to support,Dry weight Trophic level. a large population of herbivores As is true for the. 1 5 Tertiary consumers pyramid of biomass in some aquatic ecosystems. 11 Secondary consumers this could result in a pyramid of a different shape. 37 Primary consumers see Figure 13 23B, 809 Primary producers Completing the Thinking Lab on the following.
A Florida bog page will demonstrate that it is not only energy. that can be passed through a food web Certain,Primary consumers. toxic compounds can cause serious damage to,21 zooplankton. 4 Primary producers species in an ecosystem when those compounds. phytoplankton are passed from one trophic level to another. B English Channel In the next section you will learn that nutrients. Figure 13 22 The biomass pyramid in A is based on data are essential for proper growth and the repair of. collected from a Florida bog In the English Channel body tissue and that they also cycle in ecosystems. ecosystem the pyramid of biomass is inverted B,448 MHR Unit 5 Population Dynamics. Grassland BIO FACT, top level consumer The pyramid of productivity shows that primary consumers. tertiary consumer harvest more of the energy trapped during the process of. secondary consumer, A photosynthesis by eating photosynthetic organisms.
primary consumer, producer directly than secondary consumers who eat the organisms. who ate the photosynthetic organisms For humans it is. far more efficient in terms of obtaining energy to eat grain. directly rather than to eat grain fed beef The pyramid of. Deciduous forest, numbers shows that the biosphere could successfully feed. tertiary consumer far more humans if they were herbivores. secondary consumer,B primary consumer, Figure 13 23 A Many ecosystems have a trophic structure. that produces a pyramid of numbers with a broad base. B In some ecosystems however there can be fewer,producers than primary consumers. THINKING LAB, Biological Magnification 3 Describe the general patterns you find in the data in the.
table Speculate on the possible reasons for the, Background differences in concentrations of DDT measured among. Certain toxic compounds are not easily broken down by species and localities and over time. decomposers so they remain in the water or soil for long. periods of time This increases the probability that these 4 Research the specific types of prey consumed by one. compounds will be ingested by small organisms which of the bird species listed in the table Draw a biomass. are then eaten by increasingly larger organisms and passed pyramid involving this species incorporating trophic. through food webs Since each animal on a trophic level levels Include the correct quantity of DDT in ppb at. tends to eat many organisms from the level below the each level of your chart. amount of toxins taken in becomes magnified with each step DDT concentration in eggs ppb. up the food chain These compounds which accumulate in. the fatty tissues of animals have been observed to have Species Year Bay of Fundy Atlantic Ocean. diverse and often harmful effects on these organisms Leach s storm petrel 1968 no data 1460. 13 3 Energy Flow in Ecosystems 444 MHR Unit 5 Population Dynamics A ll organisms require energy for growth body maintenance such as repairing damage to body parts and reproduction and many species require energy for locomotion Energy to support these activities is released from large energy rich organic molecules during the process of cellular respiration or in a few species

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