1. C.2 Communities and Ecosystems
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. Understandings Statement Guidance C.2.U1
Most species occupy different trophic levels in multiple food chains.
C.2.U2
A food web shows all the possible food chains in a community.
C.2.U3
The percentage of ingested energy converted to biomass is dependent on the respiration rate.
C.2.U4
The type of stable ecosystem that will emerge in an area is predictable based on climate.
C.2.U5
In closed ecosystems energy but not matter is exchanged with the surroundings.
C.2.U6
Disturbance influences the structure and rate of change within ecosystems.

3. Applications and Skills
Statement
Guidance
C.2.A1
Conversion ratio in sustainable food production practices.
C.2.A2
Consideration of one example of how humans interfere with nutrient cycling.
C.2.S1
Comparison of pyramids of energy from different ecosystems.
C.2.S2
Analysis of a climograph showing the relationship between temperature, rainfall and the type of ecosystem.
C.2.S3
Construction of Gersmehl diagrams to show the inter-relationships between nutrient stores and flows between taiga, desert and tropical rainforest.
C.2.S4
Analysis of data showing primary succession.
C.2.S5
Investigation into the effect of an environmental disturbance on an ecosystem.
Examples of aspects to investigate in the ecosystem could be species diversity, nutrient cycling, water movement, erosion, leaf area index, among others.

4. 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)

5. C.2.U1 Most species occupy different trophic levels in multiple food chains.

6. Organisms exist within a food webs
C.2.U1 Most species occupy different trophic levels in multiple food chains.
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

7. 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

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
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

9. 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

10. desert tropical rainforest tagia
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
Image source: Allott, A. (2014). Biology: Course companion. S.l.: Oxford University Press.

11. Practice (Gersmehl Diagram)
We will no look at a Gersmehl diagram for a specific biome, the tropical rain forest. First read this information about a rainforest as it will help you make the diagram
Biomass is the main store of nutrients because the tropical rainforest has tall, dense vegetation with many layers and multiple species
Precipitation: rainfall is high all year
Litter has a very small store of nutrients because of the high rate of decomposition
Soil has a very small store of nutrients because of leaching and low soil fertility
Weathering is rapid because of high heat and humidity
Leaching is high because of high rainfall
Run-off is high due to such large amounts of rain that the soil cannot absorb it all

12. Answer

13. Practice (Gersmehl Diagram)

14. Answer

15. Biomass is small because of the extreme heat and lack of water
Challenge yourself! Draw a Gersmehl diagram for a desert biome. Here are the specifics you need:
Soil is rich in nutrients because there is little rain available to wash them away
Biomass is small because of the extreme heat and lack of water
Litter or topsoil is practically non-existent because it is eroded by the wind
Run off is high because there is not litter to hold on to the soil
Loss as a result of leaching is low.
**I have not included the answer for this one 

16. C.2.U3 The percentage of ingested energy converted to biomass is dependent on the respiration rate.

17. C.2.U3 The percentage of ingested energy converted to biomass is dependent on the respiration rate.

18. C.2.U3 The percentage of ingested energy converted to biomass is dependent on the respiration rate.

19. C.2.U3 The percentage of ingested energy converted to biomass is dependent on the respiration rate.

20. C.2.U3 The percentage of ingested energy converted to biomass is dependent on the respiration rate.

21. C.2.S1 Comparison of pyramids of energy from different ecosystems.

22. C.2.S1 Comparison of pyramids of energy from different ecosystems.

23. C.2.S1 Comparison of pyramids of energy from different ecosystems.

24. C.2.S1 Comparison of pyramids of energy from different ecosystems.

25. C.2.S1 Comparison of pyramids of energy from different ecosystems.

26. C.2.S1 Comparison of pyramids of energy from different ecosystems.

27. C.2.S1 Comparison of pyramids of energy from different ecosystems.

28. C.2.S1 Comparison of pyramids of energy from different ecosystems.

29. C.2.S1 Comparison of pyramids of energy from different ecosystems.

30. C.2.S1 Comparison of pyramids of energy from different ecosystems.
Net productivity of different ecosystems varies greatly
To understand why analyse the energy pyramids of the different ecosystems.
source of data:

31. C.2.S1 Comparison of pyramids of energy from different ecosystems.
Reasons for high net productivity of an ecosystem
1. High primary productivity (by producers) means more energy is available to the ecosystem.
2. The higher the efficiency of energy transfer between trophic levels the higher the net productivity. Energy transfer is typically 10%.
(5 trophic levels)
(4 trophic levels)
3. Higher the primary productivity and greater the effeciency of energy transfer mean that more energy is available at high trophic levels. This can support longer the food chains, hence and more trophic levels increasing net productivity. Ecosystems rarely have more than 4 or 5 trophic levels.

32. C.2.A1 Conversion ratio in sustainable food production practices.
In commercial (animal) food production, farmers measure the food conversion ratio (FCR). It is a measure of an animal's efficiency in converting feed mass into the desired output. For dairy cows, for example, the output is milk, whereas animals raised for meat, for example, pigs the output is the mass gained by the animal.
It is calculated by:
mass of the food eaten (g)
(increase in) desired output (g)
(per specified time period)
FCR =
For example: 8 kg of food/1 kg of weight gain = 8
Animal
FCR
Beef Cattle
5 - 20
Pigs
Sheep
4 - 6
Poultry
Salmon
The lower the FCR the more efficient the method of food production.

33. C.2.A1 Conversion ratio in sustainable food production practices.
A good (low) FCR is obtained by minimising the losses of energy by respiration, for example:
Restricting animal movement
Slaughtering the animal at a young age (older animals have higher FCRs as they grow more slowly)
Optimising feed so it is efficiently digested
Animal
FCR
Beef Cattle
5 - 20
Pigs
Sheep
4 - 6
Poultry
Salmon
How ethical are the practices that lead to a low FCR?
What is more important, efficient food production or the ethical treatment of animals?
Fish farmers are trying to lower the FCR to 1. This would mean that the amount
Of feed given to the fish would be changed into ‘fish mass’ equal to the mass of feed.
Thus, nothing is lost and everything is gained as long as the other resources are not wasted

34. C.2.U4 The type of stable ecosystem that will emerge in an area is predictable based on climate.
Biome is a geographical area that has a particular climate and sustains a specific community of plants and animals (i.e. a type of ecosystem)
Biosphere is the total of all areas where living things are found (i.e. the totality of biomes)
The main factors affecting the distribution of biomes is temperature and rainfall
These factors will vary according to latitude and longitude, elevation and proximity to the sea
Temperature is influential because it affects the rate of metabolism – the phases in the life cycles of many organisms are temperature dependent
In the same way, the availability of fresh water (both in the soil and in rivers and lakes) is critical to the growth and nutrition of organisms
Rainfall and warmer temperatures are more common near the equator and less common at the poles

35. The six major types of biome/ecosystem are outlined in the table below
C.2.U4 The type of stable ecosystem that will emerge in an area is predictable based on climate.
The six major types of biome/ecosystem are outlined in the table below

36. You don’t have to remember the individual biomes …
C.2.U4 The type of stable ecosystem that will emerge in an area is predictable based on climate.
The six major types of biome/ecosystem are outlined in the table below
You don’t have to remember the individual biomes …

37. … but, you do have to be able to analyse a climatograph
C.2.S2 Analysis of a climograph showing the relationship between temperature, rainfall and the type of ecosystem.
A climograph is a diagram which shows the relative combination of temperature and precipitation in an area.
This modified climograph (first developed by Robert Whittaker) shows the stable ecosystems/biomes that arise as a result of the relative combination of temperature and precipitation.
It is a graphical representation of the biome summary table (last slide).
… but, you do have to be able to analyse a climatograph
n.b. The biomes in regions within the dashed line are strongly influenced by other factors (e.g. seasonality of drought, fire, animal grazing).

38. C.2.S2 Analysis of a climograph showing the relationship between temperature, rainfall and the type of ecosystem.
A climograph is a diagram which shows the relative combination of temperature and precipitation in an area.
This modified climograph (first developed by Robert Whittaker) shows the stable ecosystems/biomes that arise as a result of the relative combination of temperature and precipitation.
It is a graphical representation of the biome summary table (last slide).
n.b. The biomes in regions within the dashed line are strongly influenced by other factors (e.g. seasonality of drought, fire, animal grazing).

39. Another climograph

40. Change in ecosystems over time by primary and secondary succession
Primary Succession
Secondary Succession
Begins with no life
Follows a disturbance of primary succession
No Soil
Soil is present
New area (eg a volocanic island)
Glacier retreat
Pond/lake drying up.
Old area (e.g. following a forest fire, tornado, earthquake, flood)
Lichen an mosses (acidic) begin to grow on volcanic rocks
Seeds and roots are already present
Biomass low
Biomass higher
Low Production
Slower
Higher Production
Faster

41. Ecological succession
The predictable change in species composition over time.

42. C.2.S4 Analysis of data showing primary succession.

43. C.2.S4 Analysis of data showing primary succession.
Detritivores such as worms break down organic contet
Recycle nutrients
Aerate soil

44. Species diversity is affected by 2 things
Species richness (The different types of species)
Relative abundance

45. C.2.S4 Analysis of data showing primary succession.

46. C.2.S4 Analysis of data showing primary succession.
Use the examples to analyse data showing primary succession
Changes over time in total plant species richness over time at select sites on Mount Saint Helens, WA

47. Examples of secondary succession caused by disturbance to ecosystems
C.2.U6 Disturbance influences the structure and rate of change within ecosystems.
Examples of secondary succession caused by disturbance to ecosystems
Disturbance can be natural or caused by human activity
A stable deciduous forest community
A disturbance, such as a wild fire, destroys the forest
The fire burns the forest to the ground
The fire leaves behind empty, but not destroyed, soil.
Grasses and other herbaceous plants grow back first.
Small bushes and trees begin to colonize the area
Fast growing evergreen trees develop to their fullest, while shade-tolerant trees develop in the understory.
The short-lived and shade intolerant evergreen trees die as the larger deciduous trees overtop them. The ecosystem is now back to a similar state to where it began.

48. Possible opportunities include: Abandoned settlements/fields
C.2.S5 Investigation into the effect of an environmental disturbance on an ecosystem.
Your investigation should compare a site undergoing secondary succession with a primary ecosystem. This can be extended to look at the various stages of secondary succession if local sites allow.
Possible opportunities include:
Abandoned settlements/fields
Fields recovering after fire damage
Fire breaks in woodland
Ways of measuring the affect of succession include:
Species diversity
Stem/Seedling density
Biomass
Canopy coverage / light intensity at the surface
Depth/Volume of leaf litter
Soil nutrient levels

49. C.2.U5 In closed ecosystems energy but not matter is exchanged with the surroundings.
Most natural ecosystems are ‘open ecosystems’. They can exchange energy and matter with adjacent ecosystems or environments. Examples of matter exchange are:
migration of animals
harvesting of crops
the flow of water or gases
Closed ecosystems, such as mesocosms (4.1.S2) and the Biosphere 2 project are closed ecosystems. Although energy can be exchanged (most commonly through the entry of light and the loss of heat), matter remains in the system. Water and nutrients are cycled within the ecosystem.
Closed ecosystems are of interest to Scientists as they provide insight in how extra-terrestrial habitats can be setup and maintained.

50. C.2.A2 Consideration of one example of how humans interfere with nutrient cycling.
Humans practices can accelerate the the flow of matter into and out of ecosystems. This by implication (and often design) alters the nutrient cycling in ecosystems.
Phosphate mined and converted to fertiliser.
Harvesting of crops
Biomass (including phosphates and nitrates) removed from the agricultural ecosystem
phosphates added to the agricultural ecosystem
Agriculture
phosphates added to the agricultural ecosystem
Water run-off (leaching) from agricultural fields results in build-up of phosphates and nitrates in waterways and leads to eutrophication.
Phosphates and nitrates removed from the agricultural ecosystem and added to adjacent aquatic ecosystems
Nitrate fertiliser produced from atmospheric Nitrogen
(by the Haber process)

51. Bibliography / Acknowledgments
Jason de Nys