Ecological Energetics Flashcards
(29 cards)
Food Chain
sequence of orgs each being a source of food for the next
Grazing Food Chain
starts with living plants, fed on by herbivores, fed on by carnivores
Detritus Food Chain
starts with dead organic matter fed on by detritivores and decomposers
Food Web
since an organism usually feeds on several types of organism and in turn is fed on by more than one type
Producers
autotrophic plants produce food through photosynthesis and ultimately support all other levels
Consumers
primary feed on producers
secondary feed on primary
tertiary feed on secondary
Decomposers
feed on accumulated debris of dead organic matter
Why is there rarely more than 5 trophic levels
Not all energy from one trophic level is available for next
Inefficiency of energy transfer means fifth has too little energy to support a further level
Pyramid of Numbers
Total no. of orgs at each trophic level in an ecosys
Data readily obtained - simply count within a specified area
Disadvantages Pyramid of Numbers
-some orgs difficult to determine what represents a single individual
-approach does not take into account size of org
Pyramid of Biomass
total biomass of the orgs at each trophic level in an ecosys
data obtained by weighing dry mass of orgs at diff t-levels
more representative of all material at each lvl
Disadvantages Pyramid of Biomass
requires more effort
information represents the Standing Crop - what is present in one moment in time and not what is being prod over time
Inverted pyramids possible - producers amt at moment small but is being gen exceedingly quickly
Pyramid of Productivity
Represents energy value of new material produced at each trophic level over time
Comparing rate orgs prod new material will always prod meaningful pyramid relationship
Disadvantages Pyramid of Productivity
More difficult to obtain data
Measurements need to be made over a time period
Productivity
Energy entering a trophic level that remains as energy in biomass for a given area of ecosystem in a given period of time
Primary - by plants
Secondary - by consumers
Why does most solar energy never reach the ground
Over 99% reflected back into atmosphere
or absorbed by atmosphere and re-radiated
Why will most solar energy that reaches ground not be used
Most will miss leaves altogether - less than 0.1% reaching surface
Why is only 0.5-1% incident energy actually used for PS
•some energy reflected by leaf
•some transmitted through leaf and misses chlorophyll molecules
•more than half consists of wavelengths which cannot be used in PS
•reactions of PS themselves inefficient - losing much energy as heat
Gross Primary Productivity
0.5-1% incident light energy that is converted to chemical energy and fixed by producers in PS
Net Primary Productivity
NPP=GPP-Respiration
Actual rate of production by producers
Represents energy available for new growth of plants and to all other T levels
Reasons for reduction in energy at progressive T levels
•some material not consumed - inaccessible, unpalatable or inedible
•some material mot digested - not absorbed
•some material ends up as a waste product of metabolism - excreted
•many materials used in respiration to generate ATP for active processes in org
Energy budgets
For animals
NP=C-(R+U+F)
Net Prod = Consumed - Respiration + Urine + Faeces
Herbivore Percentage Efficiency
Generally low because of difficulty digesting cellulose
Relatively high losses via egestion of faeces
Endotherms Percentage Efficiency
Low percentage efficiency because they generate heat internally to maintain high body temp
Metabolism is maintained at high rate - relatively high energy losses through resp
