1. C.2 Communities and Ecosystems part 1
Essential idea: Changes in community structure affect and are affected by organisms.
Between the two coral heads is a crown of thorns sea star. These predators graze the corals. If too successful they will change the community structure of the reef so that it becomes dominated by algae rather than coral. This in turn forces the sea star to migrate to other reefs where coral dominates the community structure.

2. C.2.U2 A food web shows all the possible food chains in a community.
A food web is a diagram that shows how food chains are linked together into more complex feeding relationships within a community
There can be more than one producer in a food web, and consumers can occupy multiple positions (trophic levels)

3. Most often, the organism is classified by its most common food source.
C.2.U1 Most species occupy different trophic levels in multiple food chains.
Many species cannot be classified as belonging to only one trophic level.
Many animals (including humans) feed on both producers and consumers – putting us on the levels of both primary and secondary consumer.
Some are even primary, secondary and tertiary consumers (e.g. A herring)
Some unicellular organisms ingest others by phagocytosis, yet also contain chloroplast for photosynthesis (Euglena)
Most often, the organism is classified by its most common food source.
Many fungi are classed saprotrophs, but feed on living organisms too (athletes foot)

4. The reef food web is very complex
C.2.U1 Most species occupy different trophic levels in multiple food chains.
The reef food web is very complex

5. Organisms exist within a food webs
C.2.U1 Most species occupy different trophic levels in multiple food chains.
The reef food web is very complex
In summary:
Organisms exist within a food webs
Food webs consist of many interlinked food chains
Therefore organisms exist in multiple food chains often at different trophic levels
When stating an organism’s trophic level, it needs to be done so relative to a particular food chain

6. Sinks for nutrient storage: Biomass (flora and fauna) Litter Soil
C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
Gersmehl diagrams were first developed in 1976, by P.F. Gersmehl, to show the differences in nutrient flow and storage between different ecosystems
Sinks for nutrient storage:
Biomass (flora and fauna)
Litter
Soil

7. Nutrient inputs into the ecosystem: Nutrients dissolved in raindrops
C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
Gersmehl diagrams were first developed in 1976, by P.F. Gersmehl, to show the differences in nutrient flow and storage between different ecosystems
Nutrient inputs into the ecosystem:
Nutrients dissolved in raindrops
Nutrients from weathered rock
Nutrient outputs (losses) from the ecosystem:
Nutrients lost through surface runoff
Nutrients lost through leaching

8. C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
Gersmehl diagrams were first developed in 1976, by P.F. Gersmehl, to show the differences in nutrient flow and storage between different ecosystems
Flows between the sinks:
Littering (including withering, defoliation, excretion, unconsumed parts left over, dead bodies of animals, and so on) *
Decomposition of the litter into inorganic nutrients, which are then stored in the soil
Nutrient uptake by plants
When used to analyse a particular ecosystem:
Diameter of sinks are proportional to the mass of nutrients stored in each sink
The thickness of the arrows are proportional to the rate of nutrient flow *
Human interactions are not considered – do not confuse littering with dropping trash

9. BIOMASS LITTER SOIL Measures flow of nutrients
C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
Gain from precipitation
Gain from weathering
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
Measures flow of nutrients
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

10. BIOMASS LITTER SOIL Biomass-living plants and animals
C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
Gain from precipitation
Gain from weathering
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
Biomass-living plants and animals
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

11. BIOMASS LITTER SOIL Soil- Dead organic matter or humus in the soil
C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
Gain from precipitation
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
Soil- Dead organic matter or humus in the soil
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

12. C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
Gain from precipitation
Gain from weathering
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
Litter- dead organic matter lying on the soil surface
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

13. Uptake Pathway: Absorption and take-up of elements from soil by plant roots
Gain from precipitation
Uptake Pathway
Fallout Pathway
BIOMASS
LITTER
Takes elements such as nitrogen, potassium and phosphorus from the soil
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

14. Fallout Pathway: Death of plants and animals and the addition of nutrients to the litter store
Gain from precipitation
Gain from weathering
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

15. Decay Pathway: Decomposition of litter to humus and return of nutrients to soil
Gain from precipitation
Gain from weathering
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

16. Gain from Weathering: Chemical elements added to soil by weathering of rocks
Gain from precipitation
Gain from weathering
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

17. Gain from Precipitation: Additional nutrients from precipitation, lightning or wind-blown dust etc.
Gain from weathering
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

18. Loss by Runoff and Leaching: Nutrient removal through the erosive movement and chemical action of water.
Gain from precipitation
Gain from weathering
Fallout Pathway
BIOMASS
Uptake Pathway
LITTER
SOIL
Decay Pathway
Loss by runoff
Loss by leaching

19. Litter (pine needles) is the main store
C.2.S3 Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
Litter (pine needles) is the main store
Slow rate of nutrient transfer between stores
Soil is the main store
Slow rate of nutrient transfer between stores (except for the transfer from biomass to litter)
Biomass is the main store (soil is nutrient poor)
Fast rate of nutrient transfer between stores
Tagia
(temperate forest)
Desert
Tropical rainforest

20. Sort into trophic levels Desiccate
C.2.U3 The percentage of ingested energy converted to biomass is dependent on the respiration rate.
Collect samples and estimate numbers of all species (including animals) in the ecosystem.
Sort into trophic levels
Desiccate
Measure mass of each tropic level. Check your results (dry again and re-weigh)
Biomass is the total dry mass of organic matter in organisms or ecosystems.
By measuring the biomass of an ecosystem, we can see how productive it is and make comparisons to pass data and ecosystems.
This could be used to measure the health of en ecosystem
Farmers may measure biomass as a method of assessing growth strategies.

21. C.2.U3 The percentage of ingested energy converted to biomass is dependent on the respiration rate.
Collect samples and estimate numbers of all species (including animals) in the ecosystem.
Sort into trophic levels
Desiccate
Measure mass of each tropic level. Check your results (dry again and re-weigh)
Biomass is the total dry mass of organic matter in organisms or ecosystems.
By measuring the biomass of an ecosystem, we can see how productive it is and make comparisons to pass data and ecosystems.
This could be used to measure the health of en ecosystem
Farmers may measure biomass as a method of assessing growth strategies.
Think: with such a destructive method how do researchers minimize the amount of organisms they have to kill?
How would you design a collection method that would give reliable data with minimal destruction?