4.4 Ecological Energetics



Energy flow- Feeding involves the transfer of energy

  • Producers- Manufactufacture organic substances from inorganic substances using light energy.   
    • Almost all plants use light energy to produce organic substances by photosynthesis 
    • Chemoautotrophs use chemical energy to produce organic compounds from inorganic energy
  • Consumers- Obtain  their energy from feeding on other organisms.                         
    • Primary consumers feed on plants = herbivores.                                         
    • Secondary consumers feed on Primary consumers = Carnivores
  • Detrites pathway- organisms involved in decay and decomposition
    • Decomposers- bacteria and fungi;
    • Detrivores- earthworms/woodlice/millipedes

Food chain- Shows the link between the producer, primary consumer and sencondary consumer. Each stage= trophic level where producers= first trophic level

Food web- The pattern of interrelated food chains that operate in an ecosystem

1 of 9

Qualitative relationships between trophic levels

Food chains and food webs show the energy flow but not the qualitative relationships between each trophic level.

A pyramid of numbers

  • Represents the total number of organisms at each trophic level:                                   Length of bar =kxNo of organisms
  • Normally there would be more oganisms at producer level>Primary >> Pyramid shape
  • :( They do not take into account the size of the organism
  • :( When v.large numbers are involved at any trophic level it is impossible to scale the bars accurately

Pyramid of energy (Productivity)  (kJm-2yr-1)

  • Reflects the new material produces over a period of time
  • :) Most accurate rep of the energy at a particular level
  • :( Values are more difficult to obtain as values need to be obatined over a period of time to compare the befor and after
  • particularly usefull in compareing ecosytems
  • Stably ecosystems are always represented as an energy flow pyramid
2 of 9

Qualitative relationships between trophic levels

Pyramid of Biomass

  • Rep The biomas of the organisms at a particular trophic level in a food chain/web
  • Fresh mass- more variable but will normally give an accurate representation
  • dry mass- drying the organisms until constant mass is achieved= more accurate 
    • :( Time consuming                         
    • :( Organisms are killed in process
  • Only the organisms present at any one time are considered
  • Inverted pyramids of biomass in a particular food chain are v.common as the consumer(s) have a number of different food sources.
  • :) More representative> Pyramid of numbers
  • :( How would you gather the fresh mass of an oak tree-> Less practical
  • :( Sometimes misleading - An oak tree could provide food for millions of leaf eating insects but should its value be represented as the mass of entire tree or just edible leaves
3 of 9

The efficiency of energy flow throughout the ecosy

Energy losses btwn sun and plants- less than 1% of the sun's energy reaching the atmospher is available to plants- over 90% of energy is reflected back into space by dust particals/clouds OR absorbed by water vapour/ dust in atmosphere then re-radiated as heat enegy

most of the energy reaching the earths surface will fall on the bare ground -> miss the leaves of the plant

Of the sun's energy that strikes a leaf, most of it is lost through

  • Being reflected from the surface of the leaves- exacerbated by thick waxy cutical
  • used in evaporation of water
  • missing chloroplasts within leaf - colume of chloroplasts in a palisade cell is v.small
  • Wrong wavelength -> Not absorbed -> reflected 
  • Photosynthetic (photochemical) reactions reactions are inefficient- much of the energy is lost as heat

Between 0.5% & 1% of the incident light that reaches the leaf surface will be converted into chemical energy as a result of photosynthesis

4 of 9

The efficiency of energy flow throughout the ecosy

Gross primary production- Energy in the organic componds produced by plants in photosynthesis

However plants use up to 50% off the GPP in Respiration (R)

Net primary production - energy available for growth or the other trophic levels of the ecosystem


5 of 9

Energy transfer between producers and consumers

  • Between producers and primary consumers- least efficient stage (5-10%)Excretory loss- a metablic waste eg- urea, represents energy that is not able to be transferred to the next trophic level.
    • much plant material cannot be accessed e.g- trunks and roots ect. 
    • V.Difficult to digest- V.few speies have the enzymes required to digest cellulose and lignin. Therefore herbivores can only assimilate a small % of the plant material
  • Energy lost as heat is produced as a by product in respiration to generate ATPSome plants / plant parts eg - laves from deciduous trees in autumn are not available to primary consumers but enter the decomposer food chain
    • Respiratory losses are particuarely high in mammals and birds (endotherms). Need to maintain a high & constant body temp and have a high metabolic activity -> high resp. rate -> heat loss

Energy transfer btwn consumers

  • Energy transfer btwn animals is typically 10-20%

Sun-> leaves = 0.5-1%        plants- P.consumers = 5-10%             P->S.consumers= 10-20%

6 of 9

Implications for agriculture

Key aims for increased efficiency or energy transfer into the plants and animals:

  • Increasing primary productivity in plants
    • Remove / reduce the limiting factors affecting growth 
      • Grow in green houses providing arxtra light, heat and CO2
      • Fertilizer and reduce effect of pests (pesticide)
      • Approprate spacing of crops in a field -> Reduce competition & Maximise coverage of and used
  • Intensive farming of domestic livestock
    • Confinement
      • less energy is used in movement
      • ensurs less land is utilised at any one time& manure is spread out more evenly over the land
    • warm conditions  indoors
      • Reduces energy required to keep to produce heat to maintain body temp
    • high energy & high protein food
7 of 9

Implications for agriculture

Ethical issues

  • Suffer hight stress levels, bone and joint damage

Management issues

  • Disease can spread much more rapidly when animals are confined in close proximity
    • Overuse of antibiotics to prevent/control disease -> anti-biotic resistant bacteria

Productivity in animals

Energy budgets:           P=C-(R+U+F)

  • R=Respiration
  • U=Urine
  • F=Faeces
  • C=Energy consumed
  • P=Net secondary productivity

Intensive farming maximises P by reducing R,U and F ->>> Increase in growth and profit

8 of 9

Energy efficiency and the human diet

  • Production of animal products is much less efficient than using crops
  • The inefficiency of energy transfer through food chains:
    • Much mor energy is available to humans through eating plant products than animal products!!!

Image result for vegetables

9 of 9


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Ecology, ecosystems and environmental biology resources »