OCR Biology A - 6.3.2 - Ecosystems Part 1
An ecosystem is the interaction between living organisms (biotic) and their non-living environment (abiotic) within a specific area, functioning together as a system.
Ecosystem
All the interactions between the living and non-living components in a defined area
Key Terms
Ecosystem
All the interactions between the living and non-living components in a defined area
Biome
Large ecosystem
Open ecosystem
When living things can move between ecosystems
Closed ecosystems
When living things cannot easily move between ecosystems e.g. islands
Niche
Role of a particular species
Biotic
Involves other living organisms
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| Term | Definition |
|---|---|
Ecosystem | All the interactions between the living and non-living components in a defined area |
Biome | Large ecosystem |
Open ecosystem | When living things can move between ecosystems |
Closed ecosystems | When living things cannot easily move between ecosystems e.g. islands |
Niche | Role of a particular species |
Biotic | Involves other living organisms |
Biotic factors affecting ecosystems | Predators Food supply (prey) Disease Cooperation between species Competition between species |
Abiotic factors affecting ecosystems | pH Conc of pollutants Temp (climatic) Moisture/ rainfall/ relative humidity O2 level Soil type (edaphic) Light intensities |
How does low light intensity affect the ecosystem | Plants develop photosynthetic pigments that require less light Grow larger leaves Reproductive systems that only work in optimum light intensities |
How does temp affect the ecosystem | Temp has the biggest effect on enzymes in the organisms that live in the ecosystem May trigger migration/ hibernation Dormancy/ leaf fall/ flowering in plants |
How are ecosystems organised | In trophic levels |
Producers in an ecosystem | Lowest trophic level Involves autotrophs, chemotrophs and photoautotrophs |
Autotrophs | Convert energy from environment into complex organic matter, then are used as respiratory substrates or for growth |
Chemo/photoautotrophs | Use light/ chemicals to convert small inorganic molecules into complex organic ones |
Consumers | Higher/est trophic levels Feed on complex organic matter made by autotrophs and other organisms and use the products of digestion as respiratory substrates or for growth 1’<2’<3’ |
Decomposers | Feed on waste or dead organsims to gain energy by digesting and respiring organic matter Recycling - returns inorganic ions to the air/soil |
Why are ecosystems dynamic | Always changing due to many interlaced intearctions that any small change causes several others–> alters flow of biomass |
Types of changes in ecosystems | Cyclical - repeated change e.g. seasons, day/night Directional - in one direction e.g.global warming, erosion Unpredictable/ erratic - no rhythm or constant direction e.g. volcanic eruption |
Trophic level | Level at which an organism feeds |
Components of an ecosystem | Habitat Population Community |
Habitat | Where an organism lives |
Population | Where all the members of a species living in some place at a given time |
Community | All the populations of diff species who live in some place at a given time, who can interact w/ each other |
Why are there fewer consumers at higher levels | Energy (biomass) is lost at each trophic level so unavailable to organism at next trophic level, therefore there’s less energy available to sustain living tissue |
How is biomass lost | Cellular respiration - conversion to inorganic molecules such as CO2 and H2O Excretory materials Indigestible matter Not everything is fit for consumption e.g. bones Transferred at metabolic heat (movement) |
Loss of biomass in endotherms vs ectotherms | Ectotherms use less energy in maintaing body heat so there is more biomass availabe |
Saprotrophs | Secrete extracellular enzymes onto dead/waste materials | Digest the materials into small molecules which are then absorbed and stored/respired |
Why is the producer efficiency v. low | Approx 90% of light is reflected, unusable wavelength and transmitted through leaf Limiting factors Energy used for photosynthetic reactions |
Succession | Progressive change in the structure and species composition in a community Affects vegetation first but then brings about corresponding changes in bacteria, fungi, insects, birds and mammals |
Climax community | Final, stable community that exists after the process of succession has occurred Usually woodland communities |
Deflected succession | Happens when succession is stopped/interfered w/ e.g. grazing so a plagioclimax develops as the species are stuck in that one stage of succession |
Pioneer species | Species that begin the process of succession, often colonising an area as the first living thing there |
Primary succession | If a community is developed from bare ground e.g. volcanic eruptions Pioneer communities start succession ---> conditions change (build up or organic material /nutrients) and other species succeed them Larger plants continuously succeed small plants until a climax community is formed |
Secondary succession | Does not start from bare ground | Takes place on a previously colonised but damaged/disturbed habitat |
Why are sand dunes helpful in terms of succession | Shows us the stages of succession in order of occurrence whereas usually we only see the current stage |
How does succession affect species diversity | Increases it however dominant species may outcompete the smaller species killing whole species off |
Weathering | Breakdown or decomposition of rock in situ |
How does weathering contribute to succession | Decomposition of rock increases soil depth/ changes soil composition Favouring new species |
Calculating net primary production | Gross primary production = npp - products of respiration |
Calculating efficiency of energy transfer | Net production/ food intake x 100 |
Plagioclimax | Sub-climax community when succession has been deflected |
Ways to deflect succession | Mainly agriculture and human activity e.g. Grazing Burning Application of fetilisers Application to herbicide Exposure to excessive amounts of wind |
How does succession affect biomass | Increases it due to more organisms in the ecosystem |
Why should sub-climax communities be conserved | Higher species diversity than climaxx communities - still contain some sub-climax species and climax species Results in conserving a much wider range of plants and animals that dont live in the climax community |
Pioneer species on sand dunes | Species that can tolerate salty water, lack of fresh water and stable sand e.g. sea rcket |