Biomass Transfer Through Ecosystems

What is the main source of energy?

Sun

Food chains and webs

Diagrams scientists use to show transfer of biomass (energy) through organisms in an ecosystem

1st trophic level

Producer

• Organism that converts light energy into chemical energy by photosynthesis

Subsequent trophic levels

Consumers

• Organisms that obtain their energy by feeding on other organisms

Primary consumer

Animal that eats producer

What is the usual maximum trophic levels go up to? Why?

Quaternary

• There is not sufficient biomass & stored energy left to support further organisms

Decomposers

Break down dead organisms, releasing nutrients back into the ecosystem

Biomass

Mass of living material present in a particular place or in particular organisms

How to calculate biomass at each trophic level

biomass present in each organism * total no. of organisms in that trophic level

• Shows biomass present at a certain moment in time; doesn’t take into account seasonal changes

Why do scientists usually calculate the ‘dry mass’ of organisms?

When measuring mass of fresh material present, water content must be discounted, but due to presence of varying amounts of water in diff organisms, this technique v. unreliable

• Unless v. large samples used

Problem w. calculating ‘dry mass’

• Organisms must be killed

• Places in oven at 80 degrees Celsius until all water evaporated

  • Shown by min. 2 identical mass readings

• Only small sample taken

  • May not be representative of population as a whole

What is biomass measured in for areas of land?

grams per square metre (gm-2)

What is biomass measured in for areas of water?

grams per cubic metre (gm-3)

What do biomass consist of & how does this make it equated to energy content?

All cells & tissues of the organisms present, including carbs & other C compounds

• C compounds are a store of energy

Why is biomass in each trophic level less than level below?

When animals eat, a small proportion of food they ingest is converted into new tissue

• Only this part of the biomass is available for the next trophic level to eat

What is the energy available at each trophic level measured in and why?

Kilojoules per metre squared per year (kJm-2yr-1)

• Allows for changes in photosynthetic production & consumer feeding patterns throughout the year

• As biomass is transferred between trophic levels, so energy contained is transferred

Ecological efficiency

The efficiency with which biomass or energy is transferred from 1 trophic level to the next

• As biomass is transferred between trophic levels, energy contained is also transferred

How to work out efficiency off biomass transfer

1. Calculate total biomass consumed

mass (per metre squared per year) * area of land

2. Efficiency of biomass transfer

(Biomass available after transfer) / (Biomass available before transfer) * 100

How much sunlight do producers convert into chemical energy / biomass

1-3%

Why do producers convert such little sunlight into biomass? (3)

1. Approx. 90% reflected, some transmitted thru leaf, some unusable wavelength

2. Other factors may limit photosynthesis, such as water availability

3. A proportion of the energy is ‘lost’, as is used for photosynthetic reactions

Gross production (Gross primary productivity)

Total solar energy plants convert to organic matter

• 20-50% used in respiration

• Remaining converted into biomass

Rate at which energy is incorporated into organic molecule in plants in photosynthesis in a given area or volume in given time

net production (net primary productivity)

Rate at which energy is transferred into organic molecules that make up new plant biomass after respiratory losses to environment have been taken into account.

How to work out energy available to next trophic level

Net production = Gross production - respiratory losses

• Can be applied to biomass or energy production within an organism

What is the generation of biomass in a producer and consumer known as?

• Producer = Primary production

• Consumer = Secondary production

What percent do consumers (at each trophic level) convert the biomass of their food to their tissue?

At most 10%

Why do consumers convert a small amount of biomass in their food to their own tissue?

• Not all of the biomass of an organism is eaten (bones, roots)

• Some energy is transferred to environment as metabolic heat (result of movement + resp.)

• Some parts eaten are not digested, these parts & their energy content are excreted as faeces

• Some energy is lost from the animal in excretory materials (pee)

How to work out efficiency of energy transfer between trophic levels

(Energy available after transfer/ Energy available before transfer) * 100

How do human activities manipulate transfer of biomass thru ecosystems?

Through agriculture, trophic levels in a food chain are minimised to maximise energy/biomass transfer to humans