Studied by 18 people
What is an ecosystem?
A community of animals, plants and bacteria interrelated with the physical and chemical environment
What are the components of an ecosystem?
Habitat- the place where an organism lives
Population- all of the organisms of one species, who live in the same place at the same time, and who can breed together
Community- all the populations of different species, who live in the same place at the same time, and who can interact with each other
What is a niche?
The role of each species in an ecosystem. A description of a niche could include how and what an organism feeds on, what it excretes and how it reproduces. Two species cannot occupy the same niche in the same ecosystems.
What are the biotic factors in an ecosystem?
Producers- plants and photosynthetic bacteria which supply chemical energy to other organisms
Primary consumers- herbivores which feed on plants and are eaten by carnivorous secondary consumers, which are eaten by carnivorous tertiary consumers
Decomposers- bacteria, fungi and some animals which feed on waste material or dead organisms
What are the abiotic factors in an ecosystem?
Humidity, pH, temperature, concentration of pollutants
Abiotic factors can be influenced by biotic factors
At extreme values of an abiotic factor, a species may perform better, worse, or die
Why are ecosystems dynamic?
They are constantly changing- the non living elements change, and the living elements grow and die, with populations rising and falling. Small changes in one thing can affect another- nitrogen levels in soil affect the population sizes of plants growing there- nitrogen fixing plants grow successfully in nitrogen deficient soil, but affect their environment by increasing the soil nitrogen levels
What are the three types of changes in an ecosystem which affect population size?
Cyclic changes- these repeat in a rhythm , for example movement of tides and changes in a day length
Directional changes- these changes go in one direction and tend to last longer than the lifetime of organisms in an ecosystem, for example coastal erosion or silt deposition in an estuary
Erratic changes- these have no rhythm or direction, for example lightning or hurricanes
What is biomass?
Organic and inorganic components making up a plant- e.g, glucose levels and mineral ions
What is biomass transfer?
Transfer of biomass from one tropic level to another
What is a trophic level?
The level at which an organism feeds in a food chain
What idea does a pyramid of numbers represent?
At each trophic level, living organisms have to carry out life processes- respiration releases energy from organic molecules, which is eventually converted to heat, and materials are lost in CO2 and H20
Biomass is lost from a food chain in dead organisms and waste material, which is then only available to decomposers
Therefore, biomass is less at higher levels of the food chain- when the organisms in a food chain are about the same size, this means there will be fewer consumers at the higher levels
What does a pyramid of numbers contain?
The area of each bar in the pyramid is proportional to the number of individuals, as an approximation for the total biomass at that level
What is a pyramid of biomass?
The area of each bar is proportional to the dry mass of all the organisms at that trophic levels
How do you calculate biomass transfer?
Ecological efficiency = (Biomass at the higher trophic level / Biomass at the lower trophic level) x 100
Ecological efficiency = (Biomass of primary consumer / Biomass of producer) x 100
What is productivity?
The rate of production of new biomass by producers
The rate at which energy passes through each trophic level in a food chain
What is gross primary productivity?
The rate at which plants convert light energy into chemical energy through photosynthesis
Why is gross primary productivity inefficient?
Because photosynthesis produces glucose, entry of biomass into the food chain is inefficient
In optimal conditions, only 40% of light energy from the sun enters the light reaction of photosynthesis and only half of this is involved in glucose production
Only two thirds of this glucose is then used for production of starch, lipids, cellulose and proteins, contributing to growth, and the rest is respired
Only a small proportion of the energy from the sun remains to enter the food chain- the net primary productivity is 8%
Why do humans manipulate environmental factors?
To make energy conversion more efficient, reduce energy loss and increase the amount of biomass which is incorporated into plants
How do humans get over light levels as a limiting factor?
Planting crops early to provide a longer growing season to harvest more light, using light banks
How can you avoid the impact of temperature on the final yield?
Growing plants in greenhouses, planting field crops early
How can nutrients be maximised?
Crop rotation, which stops the reduction of inorganic materials such as nitrate and potassium in soils
Nitrogen fixing crops that replenish nitrogen levels
Breeding crops to respond to high levels of fertiliser which provides ammonium, nitrate, potassium and phosphorous
How can pests be mitigated against?
Pesticides, breeding pest resistant plants, genetically modifying plants
How to mitigate against fungal disease
Genetically modifying, breeding crops to resist infection
How to reduce competition from weeds
Herbicides- herbicides bind to an enzyme, stopping it from working and leading to a toxic build up of the enzyme’s substrate
Why is transfer of biomass between trophic levels inefficient?
Primary consumers do not make full use of plants’ biomass- some plants die, consumers don’t make use of every part of the plant, and they don’t digest everything they eat
Even when food is digested and absorbed, much of it is respired, with only a small amount contributing to an increase in biomass and being available to the next consumer in the food chain
How can humans manipulate energy transfer?
Harvesting animals just before adulthood minimises loss of energy from the food chain
Selective breeding improves animal breeds with faster growth rates, increased egg production and increased milk production
Animals can be treated with antibiotics to avoid unnecessary loss of energy to pathogens and parasites
Mammals waste energy by finding food and keeping a stable body temperature- zero grazing and stopping animals from moving allows maximum energy for meat
Steps in saprotrophic decomposition
Saprotrophs secrete enzymes onto dead and waste material
Enzymes digest the material into small molecules, which are then absorbed into the saprotroph’s body
Having been absorbed, the molecules are stored or respired to release energy
Nitrogen fixation
azotobacter are bacteria that live freely in the soil and fix nitrogen gas, which is in the air within soil, using it to manufacture amino acids
Nitrogen-fixing bacteria such as Rhizobium also live inside root nodules of bean plants
Nitrogen fixing bacteria have a mutualistic relationship with the plant- the bacteria provide the plant with fixed nitrogen and receive carbon compounds such as glucose in return
Ammonification and nitrification
ammonium ions are released through ammonification of bacteria involved in putrefaction of proteins found in organic matter
Nitrosomonas obtain energy by oxidising ammonium ions to nitrites
Nitrobacter bacteria obtain energy by oxidising nitrites to nitrates
Denitrification
Other bacteria convert nitrates back to nitrogen gas. When the bacteria involved are growing under anaerobic conditions, such as in waterlogged soils, they use nitrates as a source of oxygen for their respiration and produce nitrogen gas and nitrous oxide
Recycling carbon
Carbon is cycled between the abiotic and biotic components of an ecosystem
Carbon cycle driven by photosynthesis and respiration
Animals, plants and microorganisms respire to release carbon dioxide.
Terrestrial plants use gaseous CO2 in photosynthesis, whereas aquatic plants use dissolved carbonates
Carbon is exchanged between the air and water when CO2 dissolves in water and reacts to form carbonic acid
Carbon enters rivers and lakes from limestone weathering in the form of hydrogen carbonate
What is succession?
Progressive change in a community of organisms over time
What is primary succession?
Development of community of plants from bare ground
Process of succession
Algae and lichens live on bare rock- pioneer community
Erosion of rock and build up of dead organic material produce soil for bigger plants, e.g. mosses and lichens to grow. These replace or succeed the algae / lichens
Larger plants succeed small plants until a final, stable community is reached- climax community
What is secondary succession?
Takes place on a previously colonised but disturbed or damaged habitat
What is a climax community?
The final stable community that exists after the process of succession has occurred
What is deflected succession?
Happens when succession is stopped or interfered with, such as by grazing or when a lawn is mowed
What is a pioneer species?
The species that begins the process of succession, often colonising an area as the first living things there
Stages of succession on a sand dune
Pioneer species like sea rocket and prickly sandwort colonise the sand just above the high water mark. These can tolerate salty water and unstable sand
Wind-blown sands build up around the base of these plants, forming a mini sand dune. When plants die, nutrients accumulate here. As the dune gets bigger, sea sandwort and sea couch grass coloniser it. Sea crouch grass has underground stems which stabilise the sand
Sea spurge / marram grass grow. Marram grass has shoots that trap sand, and as sand accumulates the shoots grow taller to stay above the dune so they can trap more sand
Other plants colonise the sand as the dune builds up. Many are leguminous such as hare’s foot clover and bird’s foot trefoil, which convert nitrogen into nitrate. With nitrate available, more species colonise the dunes, like sand fescue and viper’s bugloss which stabilise them further
Deflected succession
Landscape dominated by agriculture- hard to work out whether a particular location has reached its climax community
E.g. when grass is cut the area is being kept at one stage in succession- if the grass were left unmown succession would continue and the area would reach a climax community of woodland
The sub-climax community that results is a plagioclimax
Grazing, burning, application of fertiliser, application of herbicide, exposure to lots of wind
Succession is often deflected by human activity which makes it hard for conservationists to decide which habitats warrant conservation
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