What is an ecosystem?
An ecosystem is made up of all the living organisms that interact with one another in a defined area, and also the physical factors present in the area
Why are ecosystems dynamic?
- Ecosystems are dynamic meaning they are constantly changing
- This is a result of factors (abiotic and biotic)
What are biotic factors of an ecosystem?
- The living factors
- E.g. competition within a population or between different populations like for food, space and breeding partners. The presence of predators or food.
What are abiotic factors of an ecosystem?
- The non-living factors
- E.g. light, temperature, rainfall, water availability, oxygen availability, edaphic (soil) factors e.g. soil nutrient availability
- In an aquatic environment these may include pH and salinity (salt content) of the water
Do ecosystems have to be big?
No, they can be small like a pond
What is the main route by which energy enters an ecosystem?
- Photosynthesis
- The sun is the main source of energy. Its light energy is converted to chemical energy in plants through photosynthesis. This chemical energy is then transferred to other non-photosynthetic organisms as food
What do food chains and food webs show?
- Diagrams that show the transfer of biomass, and therefore energy, through the organisms in an ecosystem
- Each stage in the chain is known as a tropic level
What are edaphic factors as an abiotic factor?
- Edaphic factors are soil factors
- Clay (easily waterlogged), loam(not waterlogged), and sandy (doesn’t retain water and is easily eroded)
What is the first tropic level?
A producer
What is a producer?
- An organism that converts light energy into chemical energy by the process of photosynthesis
- They store energy as biomass, which gets passed along down the trophic levels
What are the subsequent trophic levels after the producer?
Consumers
What are consumers?
Organisms that obtain their energy by feeding on other organisms
What is the second trophic level?
The primary consumer - an animal that eats a producer
What are the following trophic levels after the primary consumer?
- Secondary consumer (animal that eats the primary consumer)
- Tertiary consumer (animal that eats the secondary consumer)
- Quaternary consumer (animal that eats the tertiary consumer)
What are decomposers?
Organisms that break down dead organisms releasing nutrients back into the ecosystem
What is biomass?
The mass of living material present in a particular place or in particular organisms
How is biomass calculated at each trophic level?
Multiply the biomass present in each organisms by the total number of organisms in that trophic level
What are pyramids of biomass?
- Diagrams that represent the amount of biomass at different trophic levels
- Pyramids of biomass are virtually always a pyramid shape
How is biomass measured?
- Measuring the mass of the fresh material present, but discounting water content
- Scientists usually calculate the ‘dry mass’ of organisms present. Organisms have to be killed to be dried and placed in an oven until all water has evaporated
- A small sample is taken which everyone can use, however, this sample may not be representative of the population as a whole
What is biomass measured in?
- Grams per square metre (gm^-2) for areas of land, or grams per cubic metre (gm^-3) for areas of water
Why is the biomass in each trophic level nearly always less than the trophic level below?
- Some available energy isn’t taken in by organisms in the first place
- Some energy is taken in but is used and isn’t available to the next trophic level
What is the energy available at each trophic level measures in?
kJm^-2 yr^-1 (kilojoules per metre squared per year)
What is the efficiency with which biomass or energy is transferred from one level to the next called?
Ecological efficiency
What is biomass transfer efficient like at producer level?
- Producers only convert 1-3% of the sunlight they receive into chemical energy and hence biomass because:
- Not all solar energy is used for photosynthesis - some is reflected, some is transmitted through the leaf and some is unusable wavelength
- Photosynthesis may be limited by other factors like water availability
- A proportion of energy is lost as it is used for photosynthetic reactions
