Topic 2.5

Ecosystem Function

Ecosystem Structure• There are 3 main biotic components in any ecosystem:

– Producers • Plants, algae and cyanobacteria• They are able to create food using sunlight energy• Also referred to as photoautorophs

– Consumers• Obtain energy through eating other organisms• They do not possess chlorophyll and can’t photosynthesise• Also referred to as heterotophs• They may be herbivores or carnivores

– Decomposers• Bacteria and fungi 1 2 3 • Obtain food though the breakdown of dead organic matter• Create humic material and are important in recycling nutrients• Some bacteria are chemoautotrophic decomposers (they use a similar

process to photosynthesis which uses energy from oxidation reactions rather than sunlight)

Energy Flow

• Photosynthesis

• Respiration

6CO2 + 6H2O C6H12O6 + 6O2

C6H12O6 + 6O2 6CO2 + 6H2O

• Energy flow through an ecosystem occurs by 2 processes:

Energy Flow Photosynthesis Respiration

Inputs

Outputs

Transformations

Process

Glucose, O2Light Energy, H2O, CO2

Glucose, O2 Energy, H2O, CO2

Light Energy Chemical Energy

Chemical EnergyKinetic Energy + Heat

Chlorophyll traps light energy, this energy used to split water molecules, H from water combined with CO2 to produce glucose

Oxidation reactions inside cells break down glucose to release energy

Energy Flow

• About half of the Sun’s total radiation is visible light

• Only visible light is useful for photosynthesis• Producers use very little of the visible light

available to produce biomass (about 0.06% of the Sun’s total radiation is captured by producers)– The remainder is reflected, transmitted or is not the

correct wavelength of light for photosynthesis. Photosynthesis itself is not an efficient process (typically 0.1 - 2.0% efficient)

Energy Flow

• Producers make energy available to consumers in the form of stored chemical energy (glucose)

• This energy is lost as it passes through each trophic level due to respiration and defaecation (typically 90% is lost between each level)

• Eventually all of the initial available energy is lost by being converted into heat which radiates away from the Earth. The Sun re-radiates energy to the Earth (which is therefore an Open System)

Howard Odum• Ecologist who made the first full analysis

of a whole ecosystem – Silver Spring, a stream in Florida

• He measured all inputs and outputs in terms of organic matter and energy

• He calculated productivity in kcal m-2 yr -1

• He represented his data as a productivity diagram and an ecosystem model

• In his models he developed a symbol language similar to that used in electronics

The Carbon Cycle

http://www.youtube.com/watch?v=2D7hZpIYlCA

http://www.youtube.com/watch?v=Lapu6k0WDIQ

The Nitrogen Cycle

Haber Process

Ammonia

Artificial inorganic fertilizer

The Water Cycle(The Hydrological Cycle)

Productivity

• Primary Productivity (PP)– The gain in energy or biomass by producers per

unit area per unit time• Secondary Productivity (SP)– The gain in energy or biomass by heterotrophs per

unit area per unit time

PP involves the conversion of solar energy – it is dependent on the amount of sunlight, temperature, CO2 etc.SP involves feeding or absorbtion – it is dependent on how much food is available and how efficiently it can be turned into biomass

Gross Productivity

• Gross Primary Productivity (PP)– The total gain in energy or biomass by producers per unit

area per unit time, not taking any losses due to respiration into account

• Secondary Productivity (SP)– The gain in energy or biomass by heterotrophs per unit

area per unit time, not taking any losses due to respiration and defaecation into account

Losses are caused at each trophic level by respirationYou could compare this idea to money flow - your GROSS income is the total amount of money you earn - your NET income is the amount of money you have after losses due to taxation etc.

Net Productivity

• Net Primary Productivity (PP)– The total gain in energy or biomass by producers per unit

area per unit time, taking losses due to respiration into account (R)

• Net Secondary Productivity (SP)– The gain in energy or biomass by heterotrophs per unit

area per unit time, taking losses due to respiration (R) and defaecation (F) into account

The net productivity values are more useful as they give you information about how much energy or biomass is available from one trophic level to the next

Maximum Net PP in Some Biomes

open ocean continental shelf

estuaries/forests/

coral reefs

agriculture grassland desert0

20

40

60

80

100

120

Net

Prim

ary

Prod

uctiv

ity (1

03 kJ m

-2 y

r-1)

Calculations

NPP = GPP – R

NSP = GSP – F – R

NPP

GPP (from photosynthesis)

R

R

F

NSP

Questions

1. Without referring to your notes, draw an outline of the carbon, nitrogen and water cycles

2. Why is not all of the energy assimilated by one trophic level available to the next one?

3. Without referring to your notes, write formulas for the calculation of NPP and NSP (defining each term)

QuestionsBiome Mean NPP

(kg m-3 yr-1)Desert 0.003

Tundra 0.14

Temperate grassland 0.60

Savannah 0.90

Temperate forest 1.20

Tropical rainforest 2.20

1. Compare and contrast the NPP of each biome

2. Why is there a difference between the NPP of temperate grassland and savannah?