What is an ecosystem?
Ecosystem= a balanced natural unit of living components in a given area as well as the non-living factors with which they interact.
Habitat: Natural home or environment of an organism.
Community: An interacting group of different species within a habitat.
Population: A group of interbreeding individuals of the same species, in the same environment at the same time.
Energy flow: origin
Energy comes from:
- The ultimate source of energy is sunlight.
- Green plants are producers and maunufacture simple raw materials and sugars.
- Only a small amount of light which hits the plant becomes tissue.
Energy flow: Transfer
Energy is transferred:
- The energy transfers through trophic levels.
- Energy passes between these levels as material is eaten.
- this is called a food chain.
- Herbivores feed on plants, and carnivores eat animals.
- number of links is usually limited to 4/5 links.
- Detrivores (organisms that eat non-living materials) and decomposers (microbes) obtain nutrients from faeces and dead organisms.
Energy flow: lost
Energy is lost as:
- Energy leaves the system as heat.
- large loss of energy at each level, through respiration and excretion.
Producer energy flow
Energy originates as sunlight
- The ability of a plant to trap light energy (PE) can be shown by the equation:
(quantity of light energy incooporated into plant/ quantity of light hitting the plant) x100
PE is usually greater in crop plants such as sugar cane. Efficiency depends on external factors such as light and temperature.
- Gross primary productivity is the rate at which organic products are formed, but a large amount of this is used up in respiration.
GPP-respiration = net production.
- Net production represents the food/biomass available to primary consumers.
- Secondary productivity is the rate at which secondary consumers accumulate energy in the form of tissues or cells.
Consumer energy flow
- Consumers have an energy conversion rate of about 10% (only 10% ends up as biomass).
The energy transfer between each trophic level can be calculated:
(Energy available after transfer/energy available before transfer) x 100
Why is energy efficiency so low
- A cow wont be able to eat all of the grass- e.g. the roots and woody bits will be unappetising
- The main form of energy is cellulose, which cows cannot digest without bacteria. A lot of this excreted through faeces.
- Some of the food material is eaten by other herbivores.
Carnivores are more energy efficient than herbivores, and therefore have a much higher secondary efficiency. This is because the protein they eat is much more easily digested. Only about 20% is lost in faeces and urine, compared to 60% in herbivores.
Pyramids of energy
The number of organisms, or the amount of biomass in each trophic level, can be presented in a bar chart diagram.
Pyramid of numbers
- easy to measure
- don't take size or juvenile forms into account
- may be impossible to draw to scale
Pyramid of energy
- Difficult to measure
- Give no indication of overall productivity.
- Accurate quanititaive account of feeding relationships
- Bars decrease in size rapidly because of energy lost as heat and excretion.
- Shows the quantity of energy transferred from one trophic level to the next, per unit of volume per unit of time.
- Allow the comparison of of efficency of energy transfer from one commnunity to the next.
Succession is the change in structure and species composition of a community over time.
Primary succession is the introduction of plants and animals into an area that has not been previously colonised.
Secondary succesion is the reintroduction of plants and animals into a bare environment which was previously a occupied habitat.
The different stages in a succession when particular communities dominate are known as seres.
- Bare rock colonised by algae, lichen and fungus.
- Pioneer plants begin a community of heather and mosses.
- Herbs and low growing shrubs.
- Taller shrubs
- Birch and pine maples
- Oak or beech forest
All successions involves changes in structure on community until a climax community is reached.
A climax community is a stable community which does not undergo any further succession.
Species diversity increases as does the stability of the community.
The algae and lichen break down bare rock and decompose to create soil, which is then colonised by heather and mosses etc.