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THE FLOW OF ENERGY IN ECOSYSTEMS Lecture 2 NS 5 (1st AY 2010-2011)*Parungao

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+ENERGY: defined in physics as the capacity to do work  Kinetic Energy - the energy of movement

 Potential Energy - stored energy

 Energy is measured in units called Joules (J)  One J = about 1/4 calorie  One calorie is the amount of energy

needed to raise the temperature of 1 gram of water by 1o C (Celsius)

+ENERGY: defined in physics as the capacity to do work  FIRST LAW OF THERMODYNAMICS:

Energy cannot be created or destroyed; it can only change in form

 SECOND LAW OF THERMODYNAMICS: All systems in the universe tend to go from a state of order to a state of chaos (ENTROPY)  Entropy is energy that is unavailable to

do work

+ENERGY IN BIOLOGICAL SYSTEMS  Sun: provides all the earth's

energy in the form of LIGHT

 Autotroph/Producers: an organism that captures energy and stores it in the chemical bonds of organic molecules that it manufactures from inorganic molecules

 Heterotroph/Consumers or Decomposers: an organism that eats other organisms to obtain energy

+AUTOTROPHS AND THEIR ROLE IN ENERGY FLOWS

 PHOTOSYNTHESIS: most common means by which autotrophs make organic molecules (sugar

 Overall, the chemical reaction of photosynthesis is as follows:

Light energy + plant enzymes 6CO2 + 12H2O ---> C6H12O6 + 6O2 + 6H2O

 CARBOHYDRATE: storage form for energy in plants for body structure and energy storage

 Why do plants make sugar, is it for you? NO

+PRODUCTIVITY IN ECOSYSTEMS: OVERVIEW  As plants collect solar energy and store

it as sugar, they are also BURN that sugar and USE the energy to run their own chemical reactions

 plants usually have some energy left over after photosynthesis: BIOMASS (dry weight) of the plant; it's what the heterotrophs eat, stealing the plant's hard-won energy!

+PRODUCTIVITY IN ECOSYSTEMS: OVERVIEW  GROSS PRIMARY PRODUCTION (GPP): The total

amount of light energy converted by producers into chemical energy (organic molecules, such as sugars)

 NET PRIMARY PRODUCTION (NPP): Not all of this is stored as plant biomass; left over after the plants have used the sugars they've made for themselves

 NPP = GPP – respiration  The productivity of various ecosystems can be

calculated by measuring the biomass of vegetation per unit area per unit of time. (WE WILL DISCUSS THIS LATER)

+THE 10% RULE IN ENERGY FLOWS  About 90% of the energy of one trophic level is LOST AS

ENTROPY when it is eaten by the next higher trophic level

 EXAMPLE: It takes 1,000,000J of sunlight for a plant to store 10,000J worth of biomass. If grasshoppers (primary consumers) eat those 10,000J of plant biomass, they will convert it into only 1000J of grasshopper biomass. If field mice eat 1000J of grasshopper biomass, they will convert it into only 100J of field mouse biomass. If foxes eat 100J of field mouse biomass, they will be able to convert only 10J into fox biomass

  It's this PYRAMID OF PRODUCTIVITY that shows us why environmentalists urge us to "eat low on the food chain."   The higher you go in trophic levels, the more energy is wasted at

lower levels.

+IMAGINE THIS…  To make 1 kg of human biomass, it takes 10kg of grain

  But if you eat beef, it takes 10kg of beef to make 1 kg of human, and 100kg of grain to make that 10kg of beef!

  So if you skip the cow step, you can feed more people!

 FOOD WEB: reflect its energy transfers, with producers, consumers and decomposers all contributing to the flow of energy and nutrients through the system

+TROPHIC LEVELS

 TROPHIC LEVELS: organisms at different levels of feeding   primary (1o)producers - organisms that can perform

photosynthesis

  primary (1o)consumers - organisms that eat primary producers

  secondary (2o)consumers - organisms that eat primary consumers

  tertiary (3o)consumers - organisms that eat secondary consumers

  quaternary (4o)consumers - organisms that eat tertiary

  And so on…..

 DECOMPOSERS: are a special type of consumer that can eat dead, organic matter (detritus, carrion) and convert it back into its inorganic components

+FOOD CHAIN

+FOOD WEB

+Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystems  We also can categorize animals on the basis of the exact type

of food they eat   carnivore - animal that eats meat

  herbivore - animal that eats plant matter

  omnivore - animal that eats a variety of things (plant and animal)

  detritivore - eats dead, organic matter (detritus), but does not decompose it

  insectivore - eats insects

  frugivore - eats fruits

 WHAT “VORE ARE YOU?

+ENERGY BUDGET FOR PRODUCERS

 Producers are able to capture solar energy and convert to chemical bond energy.

 Much of that energy they used for cellular respiration.

 Some of that energy is consumed by herbivores.

 Some becomes part of dead tissue and is passed on to decomposers.

 Some is stored as growth and reproduction

+ECOLOGICAL PYRAMID

  The standing crop, productivity, number of organisms, etc. of an ecosystem can be conveniently depicted using “pyramids”, where the size of each compartment represents the amount of the item in each trophic level of a food chain   Note that the complexities of the interactions in a food web are not shown in a

pyramid; but, pyramids are often useful conceptual devices--they give one a sense of the overall form of the trophic structure of an ecosystem

 A pyramid of energy depicts the energy flow, or productivity, of each trophic level

 A pyramid of numbers indicates the number of individuals in each trophic level

 A pyramid of standing crop indicates how much biomass is present in each trophic level at any one time.

producers herbivores carnivores

+INVERTED PYRAMIDS POSSIBLE?

 A pyramid of standing crop (or of numbers) may be inverted, i.e., a higher trophic level may have a larger standing crop than a lower trophic level

 This can occur if the lower trophic level has a high rate of turnover of small individuals (and high rate of productivity), such that the First and Second Laws of Thermodynamics are not violated.

biomass of producers biomass of herbivores biomass of carnivores

+ANALYSIS OF ECOSYSTEM PRODUCTIVITY

+IMPORTANT TERMS IN MEASURING PRODUCTIVITY: BIOMASS

 total weight of organic matter, both living and dead, present on a unit area of the ecosystem at any given time

 refer specifically to the plant (phytomass) or animal (zoomass) part of the biomass

 measurable plant biomass includes undecomposed litter which may be harbouring litter fauna

+IMPORTANT TERMS IN MEASURING PRODUCTIVITY: PRIMARY PRODUCTION  the total organic matter produced as a result of

photosynthesis and nutrient uptake from the soil

 referred to as gross primary production when all organic matter including that used in metabolism is taken into consideration

+ IMPORTANT TERMS IN MEASURING PRODUCTIVITY: ECONOMIC, AGRONOMIC AND BIOLOGICAL PRODUCTIVITY

 In forestry and agriculture, only the economic parts of plants or crops are harvested

 Productivity calculated from the economic harvest alone is referred to as economic productivity (Ovington, 1965) and agronomic productivity (Pearson, 1965)

+METHODS USED IN MEASURING RPODUCTIVITY

+DIRECT METHODS  The direct method is based on biomass determined by

harvesting and weighing of all organic matter present in a unit area of the ecosystem

  techniques based on various growth parameters   (a) total net production and current shoot production

  (b) shoot production and stem wood increment

  (c) stem wood increment and estimated volume increment

 Pearson (1965) estimated annual production in a different way using partially empirical formulae based on tree dimensions such as radius of trunk at base, height of tree, depth of tree canopy and the numerical density of the species studied

+ INDIRECT METHODS

 In view of the difficulties encountered in measuring productivity in complex multistrata perennial ecosystems, a number of indirect methods have been and are still being developed to measure productivity

  1. The gaseous exchange method: using rate of gas exchange as a measure of photosynthesis

 2. The use of leaf area as an index of productivity: the leaf area available for absorbing the incident light will, to a certain extent, determine the rate of photosynthesis

+ INDIRECT METHODS

 3. The use of chlorophyll content as an index of productivity: highly significant correlation exists between chlorophyll and dry matter production

 4. Use of a fraction of total production: total production has been estimated from production of only a part or parts of trees, e.g. estimating roots from the values of top growth, or total production from quantity of leaf litter

 5. Use of albedo as an index of productivity: albedo (i.e. the ratio of the amount of light reflected from the landscape to the total amount falling upon it) as an index of production; relationship existed between visible albedo and chlorophyll content

+MEASUREMENT VIA DISSOLVED OXYGEN  Oxygen is critical to the maintenance of life processes of nearly

all organisms

  Its concentration and distribution in the aquatic environment are directly dependent upon chemical and physical factors and are greatly affected by biological processes

  Therefore, the measurement of dissolved oxygen in the water can be a very important indicator of water quality

 Chemical and physical factors--such as salinity, pH, currents, and especially temperature, can affect dissolved oxygen concentration and distribution   Salinity, usually expressed in parts per thousand (PPT), is the content

of dissolved salts in the water   Generally, as temperature and salinity increase, the solubility of

oxygen in water decreases.

+WHY OXYGEN?  Since oxygen is one of the most easily measured

products of both photosynthesis and respiration, a good way to gauge primary productivity in an aquatic ecosystem is to measure dissolved oxygen

 We cannot measure gross productivity directly because respiration, which uses up oxygen and organic compounds, is always occurring simultaneously with photosynthesis — but we can measure it indirectly  We can measure net productivity directly by

measuring oxygen production in the light, when photosynthesis is occurring

 We can also measure respiration without photosynthesis by measuring O2 consumption in the dark, when photosynthesis does not occur.

+ Since net productivity = gross productivity – respiration, we can calculate gross productivity

+THE WINKLER TEST  used to determine the level of dissolved oxygen in water

samples

 used to estimate the biological activity in the water sample

 An excess of Manganese(II) salt, iodide (I-) and hydroxide (OH-) ions are added to a water sample causing a white precipitate of Mn(OH)2 to form

 This precipitate is then oxidized by the dissolved oxygen in the water sample into a brown Manganese precipitate

  In the next step, a strong acid (either hydrochloric acid or sulphuric acid) is added to acidify the solution

 The brown precipitate then convert the iodide ion (I-) to Iodine

 The amount of dissolved oxygen is directly proportional to the titration of Iodine with a thiosulphate solution

+THE SET-UP   An excess of Manganese(II)

salt, iodide (I-) and hydroxide (OH-) ions are added to a water sample causing a white precipitate of Mn(OH)2 to form

  This precipitate is then oxidized by the dissolved oxygen in the water sample into a brown Manganese precipitate

  In the next step, a strong acid (either hydrochloric acid or sulphuric acid) is added to acidify the solution

  The brown precipitate then convert the iodide ion (I-) to Iodine

  The amount of dissolved oxygen is directly proportional to the titration of Iodine with a thiosulphate solution

+FOR YOUR ASSIGNMENT: SUBMIT NEXT MEETING…AND STUDY FOR A QUIZ ON PRODUCTIVITY

Page 10 of Activity Book (answer and detach). Use Back Page if necessary..