12.3 - Energy flow

Lecture 3: 

Lecture 3 12.3 Energy Flow Through Ecosystem

OBJECTIVES: 

OBJECTIVES At the end of the lesson, students should be able to: Describe ecological pyramid in relation to trophic levels and energy transfer Explain why the food chain does not consist more than five trophic levels.

Key Terms :: 

3 Key Terms : Food chain Food web Trophic levels Ecological pyramid Energy transfer Energy loss

Energy Flow and Chemical Cycling: 

4 Energy Flow and Chemical Cycling Energy flow occurs because as nutrients pass from one population to another, the energy content is converted to heat, which dissipates into the environment. Chemicals cycle as organic nutrients are returned to the producers. Excretion Death Cellular Respiration

The Nature of Ecosystems: 

The Nature of Ecosystems Primary producers Consumers Decomposers Detritivores

Food chain: 

6 Food chain The pathway along which food is transferred from one trophic level to another, started from a source (producer) to another (consumers) through a series of feeding relationships. Energy contained in the food materials also will transfer from one organism Grass  Grasshopper  Toad  Snake  Hawk

Food Chain : 

Food Chain A path of food consumption . The successive series of organisms through which energy flows in an ecosystem. Each organism in the series eats or decomposes the preceding organism in the chain.

Food Chains: 

Food Chains (a) A simple terrestrial food chain. (b) A simple marine food chain.

PowerPoint Presentation: 

9 The number of levels in a food chain is limited (4/5) ~ energy lost to the surrounding as heat energy The producer obtain energy directly from the sunlight to produce energy-rich organic molecules (their own biomass) The consumers in a food chain can be classified as: - primary consumers (1 0 ) – herbivores that consume energy-rich plants - secondary consumers (2 0 ) – carnivores that obtain their energy from energy-rich organic molecules in herbivores - tertiary consumers (3 0 ) – carnivores that obtain their energy from energy-rich organic molecules in carnivores

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10

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11 There are 2 types of food chains , depending on whether the producers, at the base of the chain are living plants or dead plant materials: 1) grazing food chain 2) detritus food chain

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12 1) Grazing food chain Begins with living plants as the producers and move on to primary consumers(herbivores), secondary consumers (carnivores) and finally tertiary consumers. Eg : living plant leaf  caterpillar  frog  snake Based on the size of the organism in each trophic level , it can be divided into 2 types: - predatory food chain - parasitic food chain In parasitic food chain , the organisms at each level gradually become smaller and not bigger as in the predatory food chain

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13 Predatory food chain (the size of organism become bigger as the trophic level increase) Grass  grasshopper  frog  snake  owl Rice fields  rats  fleas  parasitic protozoa Parasitic food chain (the size of organism become smaller as the trophic level increase)

PowerPoint Presentation: 

14 2) Detritus food chain - Begins with dead organic matter /dead plant material as producer - Which are subsequently eaten by detritivores and their predators - Food chains in which most primary production is decomposed or consumed as detritus are termed detritus food chains. Example: Dead plant leaf  earthworm  bird  eagle

Food webs: 

Food webs Different food chains are interconnected to form a large network. Most animals use more than one species of organism as a food source The greater the number of possible routes, the more stable the particular community.

Trophic level: 

Trophic level The position that an organism occupies in food chain Eg : Plants are producers, herbivores are secondary consumer & carnivores are tertiary consumer Many animals feed at several trophic level

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Producer are at first trophic level Primary consumer are at 2 nd trophic level 2 o consumer are at 3 rd trophic level 3 0 consumer are at 4 th trophic level

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Secondary consumer Carnivore Primary consumer Herbivore Producer Tertiary consumer Top carnivore Trophic level 4 Trophic level 3 Trophic level 2 Trophic level 1

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Energy flow in an ecosystem Producers (plants and photosynthesis organisms) Heat energy (in the form of respiration, transpiration and excretion ) Consumers (animals, etc) Chemical energy Heat energy (in the form of respiration and excretion ) Sunlight

Ecological Pyramids: 

Ecological Pyramids A trophic level is composed of all the organisms that feed at a particular link in a food chain. In general, only about 10% of the energy of one trophic level is available to the next trophic level. Feeding relationship are graphically represented by plotting the energy content, number of organisms, or biomass (the total weight of organic matter) at each trophic level. Each trophic level of a food chain forms a tier on the pyramid; that is each successive trophic level is stacked on top of the level that represents its food source.

Ecological Pyramids: 

Ecological Pyramids Primary Producers Herbivores Primary carnivores Top carnivores Ecological pyramid is a graphical statement that is used to summarize and quantify the structure and functions of a community within a specific ecosystem

PowerPoint Presentation: 

3 types of ecological pyramids have been used: Pyramids of numbers , based on counting the numbers of individual organisms at each trophic level. Pyramids of biomass , which note the weight (usually total dry weight) of organisms at each trophic level. Pyramids of energy , which monitor the energy content of the organisms at each trophic level and the rate of energy flow.

The Pyramid of Numbers : 

The Pyramid of Numbers In a numbers pyramid based on trophic levels, the organisms of a given area are first counted and then grouped into their trophic levels. When this is done, a progressive decrease in the number of organisms at each successive level is often found. In an ecosystem, the population size of small animals is large and the population size of large animals is progressively smaller The energy that is available to higher trophic levels is much less that in lower trophic levels The size of predators is basically larger than the preys

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Pyramids of numbers show how the levels in the pyramids biomass are proportional to the number of individuals present in each trophic level.

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Fig. 28.13a

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Pyramids of number can be either upright or inverted (or part of it inverted) depending on whether the size of individual organism is either small (as in phytoplankton) or large (as in a tree). If the size of organisms is progressively larger, the pyramid is upright

PowerPoint Presentation: 

The number pyramid can be (partly) inverted if the base is smaller than one or more levels above it. This occurs if the size of producer is large but smaller in number Example : A single large producer such as tree Caterpillars Large tree birds Parasites Aphids Rose bush

The Pyramid of Numbers: 

The Pyramid of Numbers Advantages: -The pyramid can be constructed easily because organism (especially the large organism) can be counted easily Disadvantages: -Changes in size of the organism during its cycle (such as larvae and juvenile forms) are not taken into consideration -Problems of classifying the organism that feed at different trophic levels because an organism may feed at different trophic levels -Difficult in counting small organism that are very large in numbers -Typical pyramid shape may not produced

The Pyramid of Biomass: 

The Pyramid of Biomass Since all organisms are made of roughly the same organic molecules in similar proportions, a measure of their total dry weight is a rough measure of the energy they contain. A count of the population, multiplied by the weight of the population giving the biomass (or standing crop = total dry mass of all organisms) of a population.

PowerPoint Presentation: 

Most biomass pyramids narrow sharply (sharply decreases) from primary producers to top-level carnivores because energy transfers are inefficient.

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The pyramid of biomass may be inverted, if the average size of organisms at lower trophic levels is much smaller than the average size of organisms at higher trophic levels Example: if the size of a producer is very small and the size of the consumer is very large, the total weight of consumers may be larger at any one time. The metabolism and reproductive system of small producer will produce an output that is larger than their biomass

PowerPoint Presentation: 

The biomass of the producer are small , have short life cycle & high rate of reproduction eg: zooplankton consume the phytoplankton so quickly that the producers never develop a large population size But, the phytoplankton continue to replace their biomass at a rapid rate (because they reproduces at rapid rate), so they can support a biomass of zooplankton bigger than their own biomass Zooplankton (10g) Phytoplankton Fish (3g)

PowerPoint Presentation: 

Based on the conditions of an ecosystem, three general variations of the biomass pyramid can be developed: In terrestrial ecosystem such as grasslands, tropical rainforests – the producers are larger and live longer, so the biomass pyramid is likely to be fairly stable and have a large base. In sea and ocean ecosystems , the producers are small and do not live long and therefore the condition of the producers may vary significantly and an inverted pyramid may be produced. In lake and pond (aquatic) ecosystems , the producers are mainly very small rooted plants, tiny algae and other phytoplanktons and the consumers may be Daphnia sp. and fish. Thus, the biomass pyramid is likely to be partially inverted and has a small base.

The Pyramid of Biomass: 

The Pyramid of Biomass Advantages: -More accurate than pyramid of number because using dry weight indicator at each trophic levels Disadvantages: -Difficult to determine the biomass because it must be kill and dry of organism to obtain their dry mass -Biomass may change with time and -Comparison with wet weight is also inaccurate because the water content of organism may change -Sometimes two organism may have same mass but different amounts of energy

The Pyramid of Energy: 

The Pyramid of Energy The most fundamental and ideal way of representing relationships between organisms in different trophic levels is by means of a pyramid of energy. It shows the rate of energy flow or production at each trophic levels This has a number of advantages such as it is never inverted.

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Fig. 28.13c

The sun as a source of energy: 

The sun as a source of energy From the sun's energy which reaches the Earth, about 34% is reflected immediately from the clouds, dust in the atmosphere and the Earth’s surface

PowerPoint Presentation: 

About 66% of light energy is used for : 42% - used in biogeochemical cycle 23% - evaporation of water 1% - produce wind & waves 0.1% ( ̴about 1%) is used for photosynthesis The energy stored is the organic compounds later flow through the ecosystem with the transfer of organic material in the food chain

The sun as a source of energy: 

41 The sun as a source of energy The ultimate source of energy in ecosystems Enters an ecosystem as radiant energy (sunlight) Producers trap & use ~ by photosynthesis Energy is transformed into organic molecules Respiration breaks the molecules ~ release energy (ATP) ~ used to do work Some energy is released into environment as heat Energy flows one way & does not recycle Energy cannot be destroyed but can be changed in form

The energy transfer: 

42 The energy transfer The passage of energy in one way direction through an ecosystem ~ energy flow Energy flow occurs in food chains Primary producers  consumers (herbivores, carnivores, omnivores)  detritivores & decomposers

How energy is transferred along the food chain? PSPM 06/07: 

43 How energy is transferred along the food chain? PSPM 06/07 Food chain reflect the transfer of energy in an ecosystem Original source of energy come from the sunlight Producers trap (about 1%) light energy received for biomass production during photosynthesis Primary consumers feed on plants/ producers Energy is transferred from 1 st trophic level (producer) to the 2 nd trophic level (primary consumer) in one way energy flow 90% of the energy is lost to the environment as heat energy Only 10% of the energy is transformed to the next trophic level, thus become lesser when transferred to next trophic level Energy lost through respiration, excretion and death

How energy is transferred along the food chain? – PSPM 06/07: 

44 How energy is transferred along the food chain? – PSPM 06/07 Secondary consumers (3th trophic level) feed on primary consumers (2 nd trophic level) and get the energy from the primary consumers Energy is then transformed from second to third trophic level Tertiary consumers (4 th trophic level) feed on secondary consumers (3th trophic level) and so on There are seldom more than 5 trophic level Because large amount of energy is lost during each transfer (witihn and between each trophic level) So each trophic level received less energy than the level before it At 4 th or 5 th trophic level, only a small amount of energy is left, insufficient to support futher trophic level Thus limiting the numbers of trophic level

PowerPoint Presentation: 

45 There are usually more four or five trophic levels, and seldom more than six. Large amount of energy is lost to the environment during each transfer as heat through respiration, excretion, transpiration Each trophic level received less energy than the level below it At the 4 th or 5 th leve;, only a small amount energy left Which is insufficient energy to support further trophic level Thus limiting the number of members in the higher trophic levels Why the food chain does not consist more than five trophic levels?

PowerPoint Presentation: 

Recent work has, however, suggested that factors other than energy loss may also be important in limiting the length of food chains. Higher trophic levels become more unstable therefore can threaten with extinction  ecosystem become more unstable Energy requirement increases as trophic levels increases. Eg : predator need more energy to catch the prey The availability of sufficient food of the preferred types and territorial space may also restrict the number of end - of - chain organisms and thus the length of food chains . It is estimated that in some ecosystem as much as 80% of primary production (producers) is not eaten by primary consumers . Plants may have died and is decomposed by detritus feeders and decomposer organisms  releasing energy to environment

PowerPoint Presentation: 

There are ~ 4 - 5 trophic level because inadequate energy in ecosystem to support more than 5 trophic . ~ energy lost to the surrounding About 80-90% is lost at each transfer The shorter the food chain, the greater the energy obtained

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The sun is the original source of energy, in the form of light, for the food chain. (100,000 Units of Energy) Plants capture approximately 1% of the available light energy from the sun for biomass production by way of photosynthesis. Photosynthesis can be described chemically as: Light Energy + 6C0 2 + 6H 2 0 = C 6 H 12 0 6 + 60 2 (1,000 Units of Energy) Herbivores consume approximately 10% of the plant biomass produced in a typical food chain. (100 Units of Energy) Carnivores capture and consume about 10% of the energy stored by the herbivores. (10 Units of Energy) Figure : Model of the grazing food chain showing the movement of energy through an ecosystem.

PowerPoint Presentation: 

50 Where does all energy loss through food chain? Respiration and metabolic activity - not all the chemical energy is retained as chemical energy in the organic molecules of their tissues; lost as heat by respiration and metabolic activity -e.g. carnivore required more energy to hunt the prey compare to herbivore (± 40-80%) Excretion - Some of the energy passed on as feces through excretion to the decomposers

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51 Death (± 10%) and decomposing process - excretion/dead plants & animals ~ the basic of detritus food chain - much of the biomass not consumed by the next organisms in next trophic levels but supports the decomposers community - the decomposing process is completed when the organic matter is processed into inorganic matter & be recycled back to the environment Where does all energy loss through food chain?

Other Key Terms : : 

52 Other Key Terms : Primary productivity Net primary productivity (NPP) Gross primary productivity (GPP) Secondary production

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53 Energy loss along the food chain The study of productivity ~ production ecology ~ involves the study of energy flow through ecosystem

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54 Figure 1 : Energy flow through a grazing food chain

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55 PRIMARY PRODUCTIVITY Energy enters the biotic component of the ecosystem through the primary producers the rate at which this energy is stored in organic substances which can be used as food materials is primary productivity

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56 GROSS PRIMARY PRODUCTIVITY (GPP) The rate at which this chemical energy is stored by plants is known as gross primary productivity (in the process called photosynthesis )

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57 NET PRIMARY PRODUCTIVITY (NPP) ± 20-50 % of the GPP is used by plant - respiration/photorespiration net gain known as the net primary productivity (NPP) which potentially available to the next trophic level (heterotroph) The amount of organic matter produced available for heterotroph: NPP = GPP - R

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58 SECONDARY PRODUCTION Production of energy by heterotroph is called secondary production the fate of energy consumed by the animal : Food consumed = growth + respiration + egestion + excretion The energy remaining in heterotrophs after losses through egestion, excretion and respiration is available for growth, repair and reproduction

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