4.4 Ecological Energetics
- Created by: MCahoon665
- Created on: 03-04-19 09:41
Definitions
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
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
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
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
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
NPP = GPP - R
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%
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
- Remove / reduce the limiting factors affecting growth
- 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
- Confinement
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
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!!!
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