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. By Chris Paine https ://bioknowledgy.weebly.com/
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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.
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.
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
How ethical are the practices that lead to a low FCR?What is more important, efficient food production or the ethical treatment of animals?
C.2.S1 Comparison of pyramids of energy from different ecosystems.
1. High primary
productivity (by producers) means more energy is available to the ecosystem.
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.
2. The higher the
efficiency of energy transfer between trophic levels the higher the net productivity. Energy transfer is typically 10%.
Reasons for high net productivity of an ecosystem
(4 trophic levels)
(5 trophic levels)
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
n.b. The biomes in regions within the dashed line are strongly influenced by other factors (e.g. seasonality of drought, fire, animal grazing).
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).
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).
C.2.S4 Analysis of data showing primary succession.
Changes over time in total plant species richness over time at select sites on Mount Saint Helens, WAhttp://www.nature.com/scitable/knowledge/library/succession-a-closer-look-13256638
Use the examples to analyse data showing primary succession
1. A stable deciduous forest community2. A disturbance, such as a wild fire, destroys the forest3. The fire burns the forest to the ground4. The fire leaves behind empty, but not destroyed, soil.5. Grasses and other herbaceous plants grow back first.6. Small bushes and trees begin to colonize the area7. Fast growing evergreen trees develop to their fullest,
while shade-tolerant trees develop in the understory.8. 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.
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
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.
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.