Ecosystems 1 Flashcards
What is an ecosystem?
a defined area made up of living organisms that interact with eachother and factors present
- range in size
- are dynamic
eg. rockpool, field, tree
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 Territory Mates
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 same place at a given time
Community
All the populations of diff species who live in same 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 a community of organisms over time
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 water availability affect ecosystems?
- lack of water leads to water stress
- lack of water causes plants to wilt (water is needed to keep cells turgid and plant upright) except xerophytes
- needed for photosynthesis
How does oxygen availability affect ecosystems?
- in aquatic ecosystems fast-flowing cold water is beneficial as it contains a high O2 conc
- in water logged soil, air spaces are filled with water instead of oxygen
- needed for aerobic respiration
How do edaphic (soil) factors affect ecosystems?
different soil types have different particle sizes (which effects which organisms can survive there)
- clay - fine particles, easily waterlogged, clumps when wet
- loam - diff particle sizes, retains water, not easily waterlogged
- sandy - coarse/well separated particles, free draining, water not retained, easily eroded
What is biomass?
the mass of living material present in an organism
How is biomass transfer represented?
in food chains, food webs and pyramids of biomass
biomass at trophic level =
biomass in each organism x total no. organisms in trophic level
Why are producers not 100% efficient?
not all sunlight is converted into biomass
- some light energy is reflected or transmitted through the leaf so isn’t all used for photosynthesis
- other factors limit photosynthesis
Why isn’t all the biomass transferred between trophic levels?
- not all biomass is eaten (eg, bones, roots, etc)
- energy is lost to surroundings (as metabolic heat from movement and respiration)
- some parts of food eaten are indigestible so are egested as faeces
- some energy is lost as excretory materials (eg. urine)
ecological efficiency =
biomass transferred
_________________________ x 100
biomass before transfer (intake)
What is ecological efficiency?
efficiency which biomass is transferred from one trophic level to the next
How do human activities manipulate the transfer of biomass through ecosystems?
agriculture (environment is manipulated to favour crops being grown and animals being reared)
- plants and animals are provided with abiotic conditions they need (eg. water, warmth)
- competition from other species is removed (eg. using pesticides, fences to prevent predators)
- agriculture shortens food chains (only 2/3 trophic levels) so less energy is lost
What is decomposition?
chemical process where a compound is broken down into smaller molecules so that they are more usable and can be returned to the environment
What is a detritivore?
an organism that speeds up decay by feeding on detritus (dead, decaying matter) which breaks it into smaller pieces
- digest internally
- increases SA for decomposers to work on
eg. woodlice, earthworms
What is the difference between decomposers and detritivores?
- decomposers digest the dead matter externally (using enzymes) and then absorb it but detritivores digest it internally
- decomposers are fungi and bacteria but detritivores are animals
- detritivores break down the organic material into smaller pieces of organic material (increasing SA for decomposers) whereas decomposers break the organic material into inorganic material.
What is nitrogen fixation?
process where atmospheric nitrogen gas is combined with hydrogen to produce ammonia
N2 + H2 → NH3
-nitrogenase enzyme involved
How is nitrogen fixed by living organisms?
- by nitrogen fixing bacteria in root nodules
eg. Rhizobium - by nitrogen fixing bacteria in soil
eg. Azotobacter
How is nitrogen fixed by non-living processes?
- by Haber process
- by lightning
Define Sustainable resource
A renewable resource which is being economically exploited in such a way that it will not diminish or run out
Define interspecific competition
Competition between organisms of different species
Define intraspecific competition
Competition between organisms of the same species
Define climax community
Final stage of succession, where the community is said to be in a stable state
Define hummus
The organic component of soil formed by the decomposition of leaves and other plant material by soil microorganisms
Define plagioclimax
The stage in succession where artificial or natural factors prevent the natural climax community from forming
Define carrying capacity
The maximum population size that an environment can support
Define dominant species
The most abundant species in an ecosystem
Define seral stages
The stages of succession
What key features does a pioneer species usually have?
seeds or spores which can disperse long distances
low nutrient requirement
shallow roots
quick growing
What is a lichen? What makes it a good pioneer species?
Symbiotic mutualistic relationship between a fungi and an algae
The fungi is able to absorb mineral ions from rocks and provide them to the algae
The algae is able to photosynthesise, so creates its own organic molecules (which it can pass on to the fungus)
Why are new species able to colonise as succession progresses?
Because other species change the abiotic and biotic conditions so that new niches are created, allowing new species to colonise
Why are earlier successional species outcompeted by later successional species?
Early successional species are able to grow in hostile conditions. When the conditions become less hostile other species colonise. These new species might be able to grow/reproduce faster than the pioneer species, so the pioneer species are outcompeted.
Compare and contrast characteristics you might expect of the early and late successional plant species you might find in the UK
Early successional species = small grasses and shrubs, fast growing, small
Later successional species = taller, longer roots, slower growing, more ‘woody’, deeper roots
Why is the same climax community not found everywhere?
Because the climax community will depend on the climatic conditions in the area.
Describe and explain how succession occurs, leading to the formation of an oak woodland from bare rock
Pioneer species colonise the bare rock
Some of the individuals die and are decomposed, this increases the amount of organic matter
New niches are created, allowing new species to colonies (e.g. mosses and grasses which help to increase the amount organic matter further
Then small plants and shrubs colonise the area. They grow bigger than the mosses and grasses, blocking light and outcompeting them.
The small plants and shrubs will provide more shelter, they will decrease fluctuations in surface temperature and there will be a further increase in the amount of organic matter. Their roots can aid the break up of rocks, so increasing mineral content of the soil
Biodiversity increases as succession progresses and the ecosystem becomes more stable
Eventually larger trees will colonise and they will outcompete the earlier successional species
The woodland climax community is created
Describe and explain how succession occurs across a sand dune
Pioneer species colonise the sand dune. They are able to cope with the harsh conditions (lack of freshwater, very salty conditions, lots of wind, unstable land because the sand is constantly moving, risk of being buried by sand!)
The pioneer species are fast growing, so they are not buried by the sand
The roots of the pioneer species stabilize the sand dunes. Also, as some individuals die, there is a build up of organic matter.
The organic material improves the soil’s ability to retain water
Other species of plant are able to colonise
Some plants might have a symbiotic relationship with nitrogen fixing bacteria, so increasing the nutrient content of the soil
This allows other larger plants to colonise. The earlier successional species are outcompeted
Eventually larger trees will colonise, creating a woodland.
Describe and explain how succession could occur in a pond ecosystem leading to the formation of woodland
Seeds from pioneer species land in the pond and germinate. These grow under water and on the bottom of the pond.
As some of the individuals die and decompose there is a build up of organic matter on the bottom of the pond
This allows some plants (emergent) to start growing at the edges of the ponds
More plants die and decompose so the layer of organic matter at the bottom of the pond builds up. This causes the water to become shallower, so emergents are able to grow all across the pond. (It becomes a marsh/wetlands)
More and more organic matter builds up, so trees are able to colonise and grow. (This is called a swamp)
If the swamp dries out, a forest is formed.
What is primary succession?
When succession starts from pioneer species colonizing an area that has never had anything growing there
What is secondary succession?
When an area is returned to an earlier successional stage and succession takes place again.
What action can people take to slow down or stop succession? Why might they do this? How is this related to conservation? (an example: maintenance of acid grassland)
E.g. Remove trees, cut down trees by coppicing or pollarding, burn areas, cut grass (or use animals to graze grass)
If there are particular target species which do not occur in the climax community, then it is necessary to prevent a climax community from developing, so that the species habitat is available
What action can people take to speed up succession? Why might they do this?
E.g. planting trees (or other later successional species)
As above – if there is a species which occurs at the climax community you might want to encourage the climax community to develop more quickly
Define Population
all the organisms of one species in one area at one time
Define community
all the organisms of ALL species in one area at one time
When is random sampling used?
When you want to work out the average population of an area or compare the average of two areas
When is systematic sampling usually used?
When you want to investigate the change in a communities/population over a distance/area
Describe how you would randomly sample an area to estimate the population of stinging nettles in a field
Create a grid on the field (or on a map of the field)
Use a calculator to generate random numbers that are used as coordinates
Place the quadrate at the intersection of the coordinates
Estimate the abundance of nettles in the quadrat (e.g. using % cover)
Repeat many times so that the mean abundance calculated per quadrat is reliable
Multiple the number of plants per quadrat BY the number of times the quadrat fits into the total are of the field in order to work out the population in the whole field
Describe how you would systematically sample an area to investigate the effect of distance from a river on the population of a specific plant
Place a transect at 90O to the river
Place a quadrat at regular intervals along the transect
Estimate the abundance of the plant in the quadrat (e.g. using % cover)
Repeat the process with many transects which are parallel to each other
Plot a graph of distance on the x-axis against population of plant on the y-axis
Use spearman rank correlation to see if there is a significant correlation between them
How can a quadrat be used to measure percentage cover?
Count the number of small squares that are half or more filled with the plant
Work out what % each square is of the whole quadrat
Then multiply the number of squares half or more filled by the % each square is worth
What are the limitations of using percentage cover as a measure of abundance?
It is quite subjective
What are the advantages of using percentage cover as a measure of abundance?
It is quick and easy to do.
You don’t have to be able to identify individual plants
How can a quadrat be used to measure frequency of a plant?
Count the number of plants present in the quadrat
What are the limitations of using frequency as a measure of abundance?
It is time consuming
It cannot be used if you cannot identify individual plants
Write the equation for mark-release-recapture
DELETE IF NECESSARYYYY
Number of organisms caught in 1st sample x no of organisms caught in 2nd sample DIVIDED BY
Number of organisms marked in 2nd sample
Describe how you would use mark-release-recapture to estimate the population of bees in a county in the UK.
DELETE IF NECESSARYYYY
Capture a sample of bees
Count them
Mark them in a way which does not affect their ability to survive (e.g. using a fluorescent powder)
Release the bees, allow them to disperse and mix back into the population
Capture a second sample
Count the total second sample
Count the number of marked bees in the second sample
Use the equation to estimate population size
Take large samples to improve reliability
What are the assumptions of the mark-release-recapture methodology?
DELETE IF NECESSARYYYYY
No births and no deaths occur between the first and second sample
No emigration or immigration occur between the first and second sample
The first sample have time to mix fully into the population before taking a second sample
The mark doesn’t wear off and doesn’t affect the organisms ability to survive
How would a scientist decide how many repeats to carry out if they are doing random sampling to find out the population of a plant in a field?
Calculate a running mean as they collected each sample
Enough samples have been collected when the running mean becomes constant
How would a scientist decide how many repeats to carry out if they are using quadrats to randomly sample an area to find out the number of species present
Plot a graph with number of repeats (quadrats) on the x-axis and total number of species found on the y-axis
When the line levels off this means that new samples are not finding any new species, so stop collecting samples
How would a scientist decide how long to sample an area if they are random sampling to find out the number of species present in a number of areas
Sample for a known period of time and record how many species are found
Repeat for different periods of time
Select the optimum time beyond which further sampling doesn’t lead to any new species being found
State 2 examples of units which could be used to measure ‘biomass’?
g / m2 / month
kg / km2 / year
What is NPP?
Net primary production (NPP) is the chemical energy store in plant biomass after respiratory losses to the environment have been taken into account
What is a definition of gross primary production?
What does the GPP primarily depend on?
The total chemical energy stored in plant biomass, in a given area/volume, in a given time
This depends on the rate of photosynthesis
List the reasons why not all the energy is transferred from:
Sun 🡪 producer
Some of the radiation from the sun is reflected or absorbed (e.g. by clouds and dust) before it reaches the plant
Not all the light is the right wavelength to be absorbed by chlorophyll – so some is reflected
Some light doesn’t hit the chlorophyll molecules / chloroplasts
There might be another factor limiting the rate of photosynthesis (e.g. CO2 concentration or temperature)
Photosynthesis is not 100% efficient (so some of the energy which is absorbed is not converted into biomass)
What is a definition of net primary production?
The chemical energy stored in plant biomass after respiratory losses to the environment
What is the equation that links NPP with GPP?
NPP = GPP - R
How do you calculate net consumption of consumers?
The net production of consumers (N), such as animals, can be calculated as:
N = I – (F + R)
Where:
I represents the chemical energy store in ingested food
F represents the chemical energy lost to the environment in faeces and urine
R represents the respiratory losses to the environment.
List the reasons why not all the energy is transferred from:
Producer 🡪 herbivore (primary consumer)
The herbivore doesn’t eat all of the producer
Some parts of the producer are indigestible (so it is lost in egestion)
Some energy is lost in excretion
List the reasons why not all the energy is transferred from:
Herbivore 🡪 Carnivore
Some energy from respiration is used to allow muscle contraction and movement
Some energy from respiration is used to maintain body temperature – so it is lost as heat (only relevant for mammals)
Some parts of herbivores are indigestible to carnivores, so lost in egestion
Some energy is lost in excretion
Draw out the nitrogen cycle in full (including the names of all processes and microorganisms involved)
GO TO DISC CHAT
Draw out the phosphorus cycle in full
GO TO DISC CHAT
What is a saprobiont?
A microorganism which secretes hydrolytic enzymes. It then absorbs the products of digestion. This is called ‘extracellular digestion’
What is a saprobiont’s role in the nitrogen cycle?
Use enzymes to decompose proteins/DNA/RNA/urea
Releasing ammonia/ammonium compounds/ ions
What are mycorrhizae?
Fungi which associate with the roots of plants
How do mycorrhizae facilitate the uptake of water and ions by plants?
hey extend out from the roots of plants increasing the area from which ions and water can be absorbed
(remember there are enough mycorrhizae associated with the roots of just one oak tree that if you straightened them all out it would be long enough to wrap around the whole world!!!)
They are able to grow into rocks in the soil and extract phosphates which the plants would not be able to access otherwise
