2.5 Ecosystem Functions

Major Functions of An Ecosystem

Producers-Convert sunlight energy into organic matter

Consumers- Use living organic matter as energy to grow and develop

Decomposers- Break down the dead organic matter / return nutrients to the soil

ENERGY ENTERS THE ECOSYSTEM AS SUNLIGHT

Only 2% of the light energy falling on plant is used to create energy

The rest is reflected, or just warms up the plant as it is absorbed

Photosynthesis Process where plants use sun light

energy to create chemical energyPhotosynthesis: equation

◦6CO2 + 6H2O --> C6H12O6 + 6O2

Inputs: light energy, water, carbon dioxide

Outputs: oxygen gas, sugarEnergy transformations: Light to

Chemicalrespiration backwards!

RespirationProcess by which animals create energy

through consumption of organic molecules (sugars)

Respiration: ◦C6H12O6 + 6O2 --> 6CO2 + 6H2O

Inputs: oxygen gas, organic molecules (sugars)

Outputs: carbon dioxide, energy in ATP, waste heat

Energy transformations: chemical to heat

Photosynthesis backwards!

Photosynthesis and Respiration

Glucose / Oxygen

CO2/ Water

Energy Transfers in Ecosystem

Energy Flow Diagram

Water Cycle

Nitrogen Cycle

Carbon Cycle

Gross productivityTotal energy captured or

“assimilated” by an organism.

Measured in joules (J)Plant (Gross Primary

Productivity)◦ GPP = sunlight energy used

during photosynthesisAnimals (Gross

Secondary Productivity)◦ GSP = food eaten - energy

in faeces

Energy is stored in leaf as sugars and starches, which later are used to form flowers, fruits, seeds,

Net productivity The energy left over after organisms have

used what they need to survive.All organisms have waste energy and

respiratory loss given off as heat, metabolism (R)

Plants and animals have to use some of the energy they capture to keep themselves growing:◦ They both move water and stored chemicals around◦ Plants make flowers, fruits, new leaves, cells and

stems◦ Animals create cells and need to move muscles.

Net productivity = Gross productivity - Respiration Energy

or using symbols: NP = GP - R

Net Primary vs. Net Secondary Productivity (NPP) vs. (NSP)

Calculate Net productivity for plants and animals NPP = GPP – R PLANTS NSP = GSP – R ANIMALS

NSP

GSP

Productivity in Food WebIn a food web diagram, you can assume

that:◦ Energy input into an organism represents the GP◦ Energy output from that organism to the next

trophic level represents the NP◦ GP-NP = R (respiration energy ) and/or loss to

decomposers

?

Therefore…

The least productive ecosystems are those with limited heat and light energy, limited water and limited nutrients.◦Example biome:_______________

The most productive ecosystems are those with high temperature, lots of water light and nutrients.◦Example biome:__________________

Now check you have understood!

Draw a complete food web for an ecosystem of your choice, which should include:◦ the sun and its energy◦ named primary producers (at least 2)◦ named primary consumers (at least 3)◦ named secondary consumers (at least 2)◦ named decomposers (at least 2)◦ respiration energy loss (use red marker for this

arrow)On your diagram use arrows to show

direction of energy flow

◦ Complete this energy flow diagram: Label GPP, NPP and R for the primary

producer Add arrows to show missing energy pathways

(5 in total) Fill in the blank box to explain why some

sunlight is not fixed by plantSUN PLANT

DECOMPOSERS

RESPIRATION…………………………….(~98% of energy is here)

HERBIVORES

Draw your own energy flow diagram, rather like the one on the previous slide to show energy flows through the trophic levels in your food web. Include the following labels:◦ Start with sunlight energy◦ Include all trophic levels from your food web◦ Include arrows showing energy moving from each

trophic level to another and to decomposers◦ Show energy lost in faeces◦ Show Respiration loss (heat energy) USE RED

MARKER!◦ Label each individual arrow with a letter

(A,B,C,D,E…)◦ Use the lettered arrows to write an equation for GPP,

NPP◦ Write an equation for GSP, NSP for primary

consumers

The data in the table below relate to the transfer of energy in a small clearly defined habitat. The units in each case are in kJ m-2 yr-1

Construct an energy flow model to represent all these data Calculate the Net Productivity for

◦ Producers◦ Consumers◦ Decomposers

Trophic LevelGross

ProductionRespiratory

LossLoss to

decomposers

Producers 60724 36120 477

Herbivores 21762 14700 3072

First Carnivores 714 576 42

Top Carnivores 7 4 1

Respiratory loss by decomposers

--- 3120 ---

Producers Herbivores1st.

CarnivoresTop

Carnivores

Decomposers

60724

R=36120

477

21762

R=14700

3072

714

R=576

42

7

R=4

1

R=3120

ENERGY FLOW MODEL

NPP of Producers:60724 -(36120+477)=24127 kJ.m-2.yr-1

NSP of Herbivores:21762-(14700+3072)=3990 kJ.m-2.yr-1

NSP of Decomposers:(477+3072+42+1)-3120=472 kJ.m-2.yr-1

Calculations:

NSP of Herbivores:714 -(576+42) =96 kJ.m-2.yr-1

NSP of Herbivores:7 -(4+1) =2 kJ.m-2.yr-1

NSP of Consumers:22483

-(15280+3115)=4088 kJ.m-2.yr-1

Question:

How to measure primary productivity

1. Harvest method – measure biomass and express as biomass per unit area per unit time.

2. CO2 assimilation- measure CO2 uptake in photosynthesis and releases by respiration

3. 02 production-Measure O2 production and consumption

Measuring productivity continued4.Radiosotope method-use c14 tracer

in photosynthesis.5.Chlorophyl measurement- assumes

a correlation between the amount of chlorophyll and rate of photosynthesis.