6.5 Ecosystems Flashcards
Define climax community.
The final stable community that exists after the process of succession has occurred.
Define deflected succession.
Deflected succession happens when succession is stopped or interfered with, such as grazing or when a lawn is mowed.
Define a pioneer species.
The species that begin the process of succession, often colonising an area as the first living thing there.
Define succession.
Succession is the progressive change in a community of organisms over time.
What can cause change in a habitat?
Any change in a community of organisms that live there.
What is primary succession?
Development of a community from bare ground.
What is secondary succession?
Succession that takes place on a previously colonised but disrupted or damaged habitat.
Give an example of how primary succession takes pace.
- Algae and lichens begin to live on the bare rock. This is called a pioneer community.
- Erosion of the rock and the build-up of dead and rotting organic materials produce enough soil for larger plants like mosses and ferns to grow. They replace the algae and lichens.
- Larger plants then succeed these small plants, until a final, stable community is reached. This is called a climax community.
In the UK, what is a common climax community?
Woodland communities.
What is an easy way to see succession in a habitat?
Succession on sand dunes is easy to look at because the sand nearest to the sea is deposited more recently than the sand further away. This means that the sand just above the the high water mark is at the start of the process of succession, whereas the sand much further away already hosts its climax community.
What are the stages of succession in a sand dune habitat?
- pioneer species colonise the sand above the water mark. They can tolerate being sprayed with salty water and the unstable sand. (sea rocket, prickly sandwort)
- Wind-blown sand builds up around the base of these plants, forming a mini sand dune. As plants die and decay, nutrients accumulate. (sea couch grass grows and as they have underground stems it stabilises the sand)
- Now dune has more stability and nutrients like marram grass grows.
- As the dune builds up, other plants colonise the sand. e.g. hare’s foot clover.
What are some pioneer species you would find on a sand dune?
Prickly sandwort and sea rocket.
On a mini sand dune what plants would you find?
sandwort and sea couch grass.
Because sea couch grass had underground stems, this ill help stabilise the sand.
When the sand is more stable, what species would you find living there?
Sea purge and marram grass.
Marram grass shoots tarp wind-blown sand, and as the sand accumulates, the shoots grow taller to stay above the growing dune, trapping more sand in the process.
What is a plagioclimax community?
A Plagioclimax community is an area or habitat in which the influences of the humans have prevented the ecosystem from developing further.
In what ways can succession be deflected?
- Grazing
- Burning
- Application of fertiliser
- Application of herbicide
- Exposure to excessive amounts of wind
Why do ecologists usually study ecosystems?
To find out the abundance and distribution of a species is related to that of other species, or to environmental factors such as light intensity or soil pH.
What would you use to sample a small area? Describe what these are?
We can use quadrats. These are squares often with 1m sides, and can have strings across them every 10cm, separating it into 100 smaller squares.
What are the 2 types of data you can collect using a quadrat?
- Distribution- measuring the presence or absence of each species. Usually at least 50% of the plant needs to be in the quadrat to count.
- Abundance- numbers of individuals of each species- either counted or estimated (percentage cover).
What bit of equipment makes the percentage cover from a quadrat more accurate? How do you use it?
Using a point frame makes it more accurate. Lower it in to the quadrat, record any plants touching the needles. If the frame had 10 needles and you lower it 10 times in each quadrat, you will have 100 recordings. So every time an individual touches a needle it represents 1%.
What do you have to think about before placing quadrats?
- Where to place the quadrats
- How many samples to take
Why do you have to think about where you will place quadrats?
If you take samples from only one area of a field, the sample may be biased therefore, it won’t be representative of the whole habitat.
How do you know where to put quadrats when taking a sample? (Random sampling)
- Randomly place quadrats across the habitat, using random coordinates to plot coordinates for each one.
- Lay out 2 tape measures on 2 edges of the study site so they look like axis.
- Use calculator to generate 2 random numbers which can be used as coordinates.
How do you know where to put quadrats when taking a sample? (Systematic sampling)
Take samples at regular distances across the habitat, so you sample every part of the habitat to the same extent.
What table should you make while when recording species in different quadrats?
Make a cumulative frequency table while taking samples from across the habitat. Plot cumulative frequency against quadrat number. The point where the curve levels off tells you how many quadrats to use.
What equation can you use to estimate the size of a population of each species in a whole habitat?
Population size of a species = mean number of individuals of the species in each quadrat/ fraction of the total habitat area covered by a single quadrat
How can you measure the changes in abundance and distribution of species?
Using a transect.
What is a transect?
A line taken across a habitat.
How can you take a transect?
Stretch out a measuring tape then take samples at regular intervals along the tape. The distance between samples will depend on the length of the line you want to look at, and the density of plant you are looking at.
What are the 2 approaches to using a transect?
Line transect and belt transect
How to take a line transect?
At regular intervals, make a note of which species is touching the tape.
How do you take a belt transect?
- Interrupted belt transect -at regular intervals, place a quadrat next to the line studying each.
- Continuous belt transect- place quadrat next to the line, moving it along the line after looking in each quadrat.
What graph can you plot for a transect to show distribution and abundance of species?
A kite diagram.
Why would some conversationalists want to conserve habitats that haven’t reached their climax community?
Sub-climax communities have a higher diversity than climax communities as they still contain some sub-climax species as well as the climax species. Maintaining a range of communities that have not reached their climax means that we are conserving a much wider diversity of plants and animals that do not live in the climax community.
What is an abiotic factor?
Non-living components of an ecosystem that affect other organisms.
What is a biotic factor?
Environmental factors associated with living organisms in an ecosystem that affect each other.
Define the word ecosystem.
A community of animals, plants and bacteria interrelated with the physical and chemical environment.
Define the word habitat.
Habitat- the place an organism lives.
Define the word population.
Population- all the organisms of one species, who live in the same place at the same time, who can breed together.
Define the word community.
Community- all the populations of different species, who live in the same place at the same time, and who can interact with each other.
Define the word niche.
Niche- the role a species plays in an ecosystem.
What are some examples of biotic factors?
- Predation
- Competition
- Disease
What are some examples of abiotic factors?
- pH
- Relative humidity
- temperature
- concentration of pollutants
- Soil compactness
Why are ecosystems always changing?
For examples, populations of different species will always be rising and falling. Also, living elements always grow and die.
Why are ecosystems described as dynamic?
Ecosystems are always changing so we say they’re dynamic.
What are the 3 types of change in an ecosystem that affect population size?
- Cyclic changes
- Directional changes
- Unpredictable changes
What are cyclic changes in an ecosystem?
These changes repeat themselves in a rhythm. e.g. the way in which predator and prey species fluctuate is cyclic.
What are directional changes in an ecosystem?
These are changes that go in one direction, they tend to last longer than a lifetime of organisms in the ecosystem. Within this changes variables tend to increase or decrease. e.g. the deposition of silt in an estuary.
What are unpredictable changes in an ecosystem?
These have no rhythm and no constant direction e.g. lightning, hurricanes.
What is biomass transfer?
The transfer of biomass from one trophic level to another.
Define trophic level?
Trophic level- the level at which an organism feeds in a food chain.
Is energy in an ecosystem recycled?
Energy is not recycled, it flows through the ecosystem.
Give some examples of nutrient cycles you would find in an ecosystem?
- Nitrogen cycle
- Carbon cycle
How is energy captured into an ecosystem by plants?
Energy is captured by plants in photosynthesis to produce organic molecules like glucose from water and carbon dioxide, this energy is released from glucose during respiration. Mineral ions are also absorbed through the roots.
What is the order of the trophic levels, starting from plants?
- Producer
- Primary consumer
- Secondary consumer
- Tertiary consumer
- Quaternary consumer
What can we use to track the movements of materials and energy through the food chain?
A food web.
In a food web, what do the arrows represent?
The arrows represent the direction of energy flow. They point in the way the energy is moving.
Why is some biomass lost at each trophic level?
- Organisms need energy to carry out life processes. e.g. respiration which releases molecules like glucose. energy is also converted to heat and materials are lost by carbon dioxide and water.
- Biomass is lost as not all of an organism can be digested e.g. cellulose, bones, hair.
What happens to biomass at higher levels of the food chain?
There is less biomass in higher trophic levels.
What can ecologists draw to represent the biomass in each trophic level in an ecosystem?
A pyramid of numbers or a pyramid of biomass.
In a pyramid of biomass, what is each bar proportional to?
The bar is proportional to the dry mass of all the organisms in that trophic level.
Why would some people chose a pyramid of biomass over a pyramid of numbers?
Counting the number of organisms does not always provide an accurate picture of how much biomass exists at each trophic level.
How can an ecologist measure the dry mass of a trophic level?
An ecologist collects all the organisms and puts them into an oven at 80° until all the water in them has evaporated. Once the mass has stopped reducing, they can be certain all the water has evaporated.
What is the disadvantage of finding the biomass of a trophic level for a pyramid of biomass? How do ecologists get around this?
Drying out organisms can be very destructive, so ecologists often just measure the wet mass of the organisms and calculate the dry mass on the basis of previously recorded data.
What equation do you use to calculate the efficiency of biomass transfer?
Ecological efficiency= (biomass at the higher trophic level/ biomass at the lower trophic level) x100
why would 2 species never occupy the same niche in an ecosystem?
As each species interacts with biotic and abiotic factors, eats particular things, reproduces and excretes in particular ways, it would be impossible for two species to occupy exactly the same niche, as they would be in direct competition. Eventually one species or the other would evolve to become a better competitor and would out-compete the other species.
What is the difference between a producer and a consumer?
Producers gain their energy from the environment (usually the Sun). They use this energy to produce biomass by converting small inorganic molecules (CO2 and H2O) to large organic molecules that contain more energy. Consumers gain their energy and biomass by eating other organisms.
At the bottom of the ocean, there is no light, where does the producers get their energy from?
The producers are thermophilic bacteria and they use chemical energy.
In what ways are energy and materials lost from a food chain?
Energy is lost as heat via respiration and in biomass that is not eaten; materials are lost in excretion (carbon dioxide, water and nitrogenous waste), and in dead organisms and waste material that are not consumed
Why may ecologists prefer to draw a food web instead of a food chain?
A food web is more realistic than a food chain – each trophic level usually consists of more than one species of organisms and most consumers will eat more than one type of organism.
Why may ecologists prefer to draw a pyramid of biomass instead of a pyramid of numbers?
A pyramid of numbers does not reflect the varying sizes of organisms at each trophic level. A pyramid of biomass provides a more accurate picture of how much biomass exists at each trophic level.
Why are there fewer individuals at higher trophic levels in a good chain?
Energy and materials are lost as they flow through the trophic levels; there is less available for those organisms at higher trophic level
Why do most food chains only have 5 trophic levels?
There is not enough energy or material in the fifth level to sustain a viable population of organisms in the sixth level.
How does a pyramid of biomass help to show how energy is lost from a food chain between trophic levels?
Biomass contains chemical energy. Energy is lost between trophic levels and so the biomass decreases between trophic levels. The pyramid shape is a visual representation of this energy loss.
Why are ecologists interested in dry mass rather then wet mass?
because wet mass can vary with different conditions and different organisms have different water content in their bodies.
Define productivity.
Productivity- the rate of production of new biomass by producers.
What is a measure of productivity in an ecosystem?
The rate at which energy passes though each trophic level in a food chain is a measure of it’s productivity.
What is gross primary productivity?
Primary productivity- rate at which plants convert light energy into chemical energy through photosynthesis.
Why is converting light energy into chemical energy inefficient in the food chain?
- Only 40% of light energy from the sun enters the light reaction for photosynthesis- only half is involved in glucose production.
- ⅔ of the glucose is used for production of starch, cellulose, lipids and proteins contributing to growth- the rest is respired.
- Hence, only a small proportion of energy from the sun remains in the food chain.
What is net primary production?
The amount of light energy that stays in the food chain.
In what ways can humans improve primary production?
- Selectively breeding plants
- Greenhouses
- Crop rotation
- pesticides
- Fungicides
- Herbicides
Give an example of how selectively breeding plants have improved primary production.
Drought resistant strains have been bred, for example, drought-resistant barley in North Africa, wheat in Australia and sugar beet in the UK.
How does growing plants in greenhouses improve primary production?
Provides a warmer temperature, increases the rate of photosynthesis which increases the rate of production of biomass. Planting crops early to provide a longer growing season also helps to avoid the impact of temperature on final yield.
How does crop rotation improve primary production?
Crop rotation can help growing a different crop in each field on a rotational cycle. This stops the reduction in soil levels of inorganic materials such as nitrate or potassium. Including a nitrogen fixing crop like peas.
What does primary production involve?
Plants
What does secondary production involve?
Animals
In what ways can humans improve secondary productivity?
- Harvesting animals just before adulthood
- Selective breeding
- Being treated with antibiotics
- Not being able to move/ zero grazing
How does harvesting an animal jut before adulthood improve secondary production?
A young animal invests a larger proportion of it’s energy into growth than an adult. Harvesting animals just before adulthood minimises loss of energy from the food chain.
How does selective breeding improve secondary productivity?
Selective breeding has been used to improve animal breeds with faster growth rates, increased egg production and increased milk production.
How does treating animals with antibiotics improve secondary productivity?
Animals may be treated with antibiotics to avoid unnecessary loss of energy to pathogens and parasites.
How does selective zero grazing improve secondary productivity?
Mammals and birds waste a lot of energy finding food and keeping their body temperatures stable. Zero grazing for a pig and cattle farming maximises energy allocated to muscle by stopping the animals moving about, by supplying food to them, and keeping the environment temperature constant.
What are saprotrophs?
Organisms that feed saprotophically, including bacteria and fungi. They are involved in the decomposition.
What do saprotrophs do?
- 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 adsorbed, the molecules are stored or respired to release energy.
What would happen if bacteria and fungi did not break down dead organisms?
If bacteria and fungi did not break down dead organisms, energy and valuable nutrients would remain trapped in the dead organism.
Why is nitrogen impossible for plants to use directly?
Nitrogen is very unreactive. Therefore, plants need a supply of ‘fixed’ nitrogen such as ammonium ions or nitrate ions.
How can nitrogen fixation occur?
Nitrogen fixation occurs when lightning strikes or through the Haber process in making fertiliser (this accounts for 10% of nitrogen fixation). Nitrogen fixing bacteria supply the rest of it.
What are the nitrogen fixing bacteria?
- Azotobacter are bacteria that live freely in the soil and fix nitrogen gas, which is in the air in the soil, using it to manufacture amino acids.
- Rhizobium are bacteria that live in the root nodules of plants of plants such as peas and beans
What is the relationship like between plants and nitrogen fixing bacteria?
The nitrogen-fixing bacteria have a mutualistic relationship with the plant: the bacteria provide a plants with a fixed nitrogen and receive carbon compounds such as glucose in return.
How do the nitrogen fixing bacteria work?
Proteins such as leghaemoglobin in the nodules absorb oxygen and keep the conditions anaerobic. Under these conditions, the bacteria use an enzyme, nitrogen reductase, to reduce nitrogen gas to ammonium ions that can only be used by the host plant.
What is released during ammonification?
Ammonium ions
How are ammonium ions released via ammonification?
Ammonium ions are released through ammonification by bacteria involved in putrefaction of proteins found on dead or waste organic matter.
What o chemouautrotrophic bacteria do to cause nitrification?
Rather than getting their energy from the sunlight (like photoautotrophic bacteria), chemoautotrophic bacteria in the soil get energy from oxidising ammonium ions to nitrates and others by oxidising nitrites to nitrates.
What is an umbrella term for the bacteria involved in nitrification?
Chemoautotrophic bacteria
What substance does nitrification need to occur?
Nitrification needs oxygen as the ammonium ions and nitrates are being oxidised. Therefore, these reactions only happen in well-aerated soils.
After nitrification, what does a plant absorb from the soil? What will it use it for?
Nitrates can be absorbed from the soil by plants and used to make nucleotide bases ( for nucleic acid) and amino acids(for proteins).
What is denitrification?
Process of converting nitrates back into nitrogen gas.
How does denitrification occur?
Some bacteria convert nitrates back into nitrogen gas. When bacteria are growing under anaerobic conditions, such as waterlogged soils, they use nitrates as a source of oxygen for their respiration and produce nitrogen gas and nitrous oxide.
What is nitrogen fixation, nitrification and denitrification?
- Nitrogen fixation- conversion of atmospheric nitrogen into nitrate or ammonium.
- Nitrification- oxidation of ammonium to nitrite and nitrate.
- Denitrification- conversion of nitrates to nitrogen gas.
What is the carbon cycle driven by?
Respiration and photosynthesis.
What is the main form of carbon which cycles carbon between abiotic and biotic components?
Carbon dioxide.
What are some ways the the carbon cycle acts in biotic components in an ecosystem?
- Animals, plants and microorganisms respire to release carbon dioxide.
- Terrestrial plants use gaseous carbon dioxide in photosynthesis.
- Aquatic plants use dissolved carbonates for photosynthesis.
How can carbon enter rivers?
Carbon can enter lakes from weathering of limestone and chalk in the form of hydrogen carbonate.
How is carbon exchanged between the air and water?
Carbon dioxide dissolves in the water and then reacts to form carbonic acid.
Why has the balance of carbon in our atmosphere changed across the last centaury?
Combustion of fossil fuels has increased.
Draw a diagram of the nitrogen cycle.
What bacteria are involved in nitrogen fixing?
- Azobacter
- Rhizobium
What bacteria is involved in nitrification? What do they do?
- Nitrosamonas bacteria- turns ammonium to nitrites (NH4+ to NO2-)
- Nitrobacter bacteria- turns nitrites to nitrates (NO2- to NO3-)
