6.3.1 - Ecosystems Flashcards
Define ecology
The study of the relationships between organisms and their environment
What is an ecosystem ?
An ecosystem is made up of all the living organisms that interact with one another in a defined area
What is meant by ecosystems being dynamic ?
They are always changing
What are the two main groups of factors that affect an ecosystem ?
Abiotic and biotic factors
What are biotic factors ?
- Living factors
- Such as organisms and the sizes of their populations
What are abiotic factors ?
- The non living or physical factors
- Such as the amount of rainfall received
What do biotic factors refer to ?
They refer to the interactions between organisms that are living or have once lived
What do biotic factors often involve ?
- They often involve competition
- Either interspecific or intraspecific
What do animals compete for ?
- Food
- Space
- Breeding partners
List some of the main abiotic factors
- Light
- Temperature
- Water availability
- Oxygen availability
- Edaphic (soil) factors
How are plants affected by light availability ?
Light is required for photosynthesis
What is the correlation between light availability and a plant species ?
In general, the greater the availability of light, the greater the success of a plant species
How do plants in low light adapt ?
- They might have larger leaves
- They may develop photosynthetic pigments that require less light
What does temperature affect the most ?
Enzymes controlling metabolic reactions
When do plants develop more rapidly ?
- In warmer temperatures
Define ectothermic animals
Animals that cant control their internal temperature, and so are more affected by the external environment
Define endothermic animals
Animals that control their internal temperature, and so are less affected by the external environment
What can changing temperatures in an ecosystem cause in animals ?
- Migration
- Hibernation
What can changing temperatures in an ecosystem cause in plants ?
Leaf fall, dormancy and flowering
What does a lack of water lead to in most animals and plants ?
Leads to water stress, which will lead to death
What does water cause plants to do ?
It causes them to wilt
Why does water cause plants to wilt ?
Water is required to keep cells turgid and so keep the plant upright
Why is it key to have cold water in aquatic ecosystems ?
A fast flowing cold water system as it contains high concentrations of oxygen
What happens if the water becomes too warm or the flow rate becomes too slow?
- Drop in oxygen concentration
- Can lead to the suffocation of aquatic organisms
How else is oxygen reduced for plants ?
In waterlogged soil, the air spaces between the soil particles are filled with water
What are the three main types of soil ?
- Clay
- Loam
- Sandy soil
Describe clay
- Fine particles
- Easily waterlogged
- Forms clumps when wet
Describe loam
This has different sized particles, retains water but does not become waterlogged
Describe sandy soil
- coarse well separated particles
- allow free draining
- does not retain water
- easily eroded
What is an ecological niche ?
It is a way of life that is unique to that species and describes its role in a community
What does an ecological niche describe ?
- The conditions necessary for survival of the species
- The species’ role in the ecosystem
How are niche and habitat different ?
While many species may share a habitat, that is not true of a niche
What are food chains and food webs ?
These are diagrams that scientists use to show the transfer of biomass and therefore the transfer of energy
What is a trophic level ?
Each stage in the food chain
How many trophic levels do food chains normally have ?
5
Why do food chains rarely have more than 5 trophic levels ?
There is not sufficient biomass and stored energy left to support any further organisms
What is the order of levels in the food chain ?
Producer —> consumer —> secondary consumer —> tertiary consumer —> quaternary consumer
What are producers ?
An organism that converts light energy into chemical energy by the process of photosynthesis
What are consumers ?
Organisms that obtain their energy by feeding on other organisms
What are decomposers ?
Decomposers break down dead organisms, releasing nutrients back into the ecosystem
How can food chains be presented diagrammatically ?
As a pyramid of numbers, with each level representing the number of organisms at each trophic level
Define biomass
The mass of living material present in a particular place or in particular organisms
How do you calculate biomass at each trophic level ?
Multiply the biomass present in each organism by the total number of organisms in that trophic level
How can this information be displayed diagrammatically ?
Pyramid of biomass
How do you measure biomass ?
Measure the mass of fresh material present
What do you have to take into account when measuring biomass ?
Water content must be discounted
What do scientists use to calculate biomass instead ?
You have to use the dry mass of the organism present
What are the problems involved with calculating dry mass ?
Organisms have to be killed in order to be dried
What are the units in measuring biomass ?
- Grams per square metre (land)
- Grams per cube metre (water)
Why is biomass in each trophic level nearly always less than the trophic level below ?
- When animals eat, only a small proportion of the food they ingest is converted into new tissue
What are the units for energy available at each trophic level ?
Kilojoules per metre squared per year
Why is energy worked out per year ?
To allow for changes in photosynthetic production and consumer feeding patterns throughout the year
What does a pyramid of energy show ?
The amount of biomass or energy converted to new biomass by each trophic level in a food chain
Define ecological efficiency
The efficiency with which biomass or energy is transferred from one trophic level to the next
What percentage of sunlight do producers turn into biomass ?
1% - 3%
Why is the percentage producers turn into biomass so low ?
- Approximately 90% is reflected
- Some is transmitted through the leaf
- Some is of unusable wavelength
- A proportion of the energy is lost, as it used for photosynthetic reactions
Define gross production
The total solar energy that plants convert to organic matter
How much of this energy is used in respiration for a plant ?
20%-50%
What happens to the energy that is not used in respiration ?
- Converted into biomass
- This is the energy available to the next trophic level
What is the net production ?
Gross production - respiratory losses
Define primary production
The generation of biomass in a producer
Define secondary production
The generation of biomass in a consumer
How much of the biomass in the food of consumers is converted into organic tissue ?
10%
Why is the efficiency at the consumer level so low ?
- Not all of the biomass of an organism is eaten, e.g. bones
- Some energy os transferred to the environment as heat through movement and respiration
- Some parts of an organism are indigestible, these parts are egested
- Some energy is lost from the animal in excretion
What does agriculture involve ?
Agriculture involves the manipulation of the environment to favour plant species that we can eat and to rear animals for food
Give examples of how conditions are manipulated by humans
- They are provided with abiotic conditions that they need to thrive such as watering and warmth
- Competition from other species is removed
- The threat of predators is removed
In a natural ecosystem what trophic level would humans occupy ?
The second, third or fourth trophic level
What is the relation between agriculture and food chains ?
Agriculture creates very simple food chains
What does a simple food chain ensure ?
- Minimum energy is lost since there are fewer trophic levels
- This ensures that as much energy as possible is transferred into biomass that can be eaten by humans
What is decomposition ?
A chemical process in which a compound is broken down into smaller molecules
What must happen to essential elements for them to be used by organisms ?
They must be processed into inorganic elements and compounds with a more usable form
What is a decomposer ?
An organism that feeds on and breaks down dead plant or animal matter, thus turning organic compounds into nutrients
How do decomposers obtain their energy ?
- From dead or waste organic material
- They are saprotrophs
What is this called (decomposer nutrition) ?
Saprobiotic nutrition
How do decomposers digest this food ?
- Externally by secreting enzymes onto dead organisms or organic waste matter
- The enzymes break down complex organic molecules into simpler soluble molecules
- The decomposers then absorb the molecules
What are detritivores ?
They are another class of organism involved in decomposition
What is a detritivores main role ?
They help to speed up the decay process by feeding on detritus (dead and decaying material)
How do detritivores speed up the decay process ?
They break down the detritus into smaller pieces of organic material, which increases the surface area for the decomposers to work on
Why is nitrogen essential ?
For making amino acids and nucleic acids in both plants and animals
Where do animals get nitrogen from ?
The food they eat
Where do plants get nitrogen from ?
From their environment
What needs to happen to nitrogen for it to be used by living organisms ?
It needs to be combined with other elements such as oxygen or hydrogen
What is the role of bacteria in the nitrogen cycle ?
Converting nitrogen into a form useable by plants
What would happen to ecosystems without nitrogen ?
Nitrogen would become a limiting factor for those ecosystems
Give two examples of nitrogen fixing bacteria
- Azotobacter
- Rhizobium
What do nitrogen fixing bacteria contain ?
The enzyme nitrogenase
What is the role of the enzyme nitrogenase ?
It combines atmospheric nitrogen with hydrogen to produce ammonia
Why is nitrogen converted to ammonia ?
This is because it can be absorbed and used by plants
What is azotobacter an example of ?
Free living soil bacterium
What is rhizobium an example of ?
Nitrogen-fixing bacteria that live inside root nodules
What are root nodules ?
These are growths on the roots of leguminous plants such as peas and beans
What kind of a relationship do the bacteria and plant have ?
A symbiotic mutualistic relationship
How does the plant gain from its relationship with the bacteria ?
Amino acids which are produced by fixing nitrogen gas in the air into ammonia in the bacteria
How does the bacteria gain from its relationship with the plant ?
Carbohydrates produced by the plant during photosynthesis
What is nitrification ?
The process by which ammonium compounds in the soil are converted into nitrogen containing molecules that can be used by plants
What is also involved in nitrification ?
Free living bacteria in the soil called nitrifying bacteria
What kind of a reaction is nitrification ?
Oxidation reaction
What are the two steps of nitrification ?
- Nitrifying bacteria (nitrosomonas) oxidise ammonium compounds into nitrites
- Nitrobacter oxidise nitrites into nitrates
Why are nitrate ions able to enter a plant ?
They are highly soluble, and are therefore the form in which most nitrogen enters a plant
What is denitrification ?
When denitrifying bacteria convert nitrates in the soil back to nitrogen gas
When does denitrification happen ?
In anaerobic conditions such as waterlogged soils
What is ammonification ?
The process by which decomposers convert nitrogen containing molecules in dead organisms into ammonium compounds
What are the main two reasons that CO2 levels fluctuate throughout the day ?
- Photosynthesis
- Respiration
How does photosynthesis affect CO2 levels ?
- It only takes place in the light
- So during the day CO2 is removed from the atmosphere, not the night
How does respiration affect CO2 levels ?
It is carried out during the day and the night, releasing CO2 constantly
When are atmospheric CO2 levels higher ?
Atmospheric CO2 levels are higher at night than the day
When do localised CO2 levels fluctuate ?
Seasonally
What does CO2 levels fluctuating seasonally mean ?
CO2 levels are lower on a summers day than a winters day, as photosynthesis rates are higher
What are the two main reasons that CO2 levels have increased greatly over the last 200 years ?
- Combustion of fossil fuels
- Released CO2 into the atmosphere from carbon that has previously been trapped for millions of years
- Deforestation
- Removed significant quantities of photosynthesising biomass.
- Less carbon dioxide is removed from the atmosphere
- Cleared forests are burnt, releases more CO2
What is succession ?
A process by which ecosystems change over time
Why does succession occur ?
As a result of changes to the environment, causing the plant and animal species present to change
What are the two types of succession ?
- Primary succession
- Secondary succession
What is primary succession ?
- This occurs on an area of land that has been newly formed or exposed such as bare rock
- There is no soil or organic matter
How is primary succession still taking place ?
- Volcanoes erupt, depositing lava
- Sand is blown by the wind to create new sand dunes
- Silt and mud are deposited at river estuaries
- Glaciers retreat depositing rubble and exposing rock
What is secondary succession ?
This occurs on areas of land where soil is present, but it contains no plant or animal species
What is each step of succession called ?
Seral stage
Describe the brief outline of a seral stage
At each seral stage key species can be identified that change the abiotic factors, especially the soil, to make it more suitable for the subsequent existence of other species
What are the main seral stages ?
- Pioneer community
- Intermediate community
- Has many other seral stages within it
- Climax community
What does primary succession begin with ?
The colonisation of an inhospitable environment
What is a pioneer species ?
A species that colonises an inhospitable environment
How do pioneer species arrive ?
They arrive as spores or seeds carried by the wind from nearby land masses or sometimes by the droppings of birds or animals that pass through
What are some adaptations of pioneer species ?
- Ability to produce a large quantity of seeds or spores
- Seeds that germinate rapidly
- The ability to photosynthesise to produce their own energy
- Tolerance to extreme environments
- The ability to fix nitrogen from the atmosphere
How is the basis of soil formed ?
The weathering of bare rock produces particles that form the basis of a soil
How does the soil obtain organic products ?
When organisms of the pioneer species die and decompose small organic products are released into the soil
What is the organic component of soil called ?
Humus
What does humus allow the soil to do ?
The soil becomes able to support the growth of new species of plant, known as secondary colonisers
How do secondary colonisers arrive ?
As spores and seeds
What happens as the environmental conditions improve ?
New species of plant arrive
What are these known as ?
Tertiary colonisers
How do tertiary colonisers survive ?
- These species can survive in conditions without an abundance of water
- However, they need to obtain most of their water and mineral salts from the soil
What happens at each stage of the intermediate community ?
The rock continues to be eroded and the mass of organic matter increases
What happens when organisms decompose ?
They contribute to a deeper, more nutrient rich soil, which retains more water
What does more nutrient rich soil allow for ?
- More favourable abiotic conditions
- Initially for small flowering plants then shrubs then small trees
Can the intermediate community have many seral stages ?
- Yes
- Seral stages continue until climax conditions are obtained
What happens at each different seral stage in the intermediate community ?
- Different plant and animal species are better adapted to the current conditions in the ecosystem
- They then outcompete many of the species that were previously present and become the dominant species
What is the final seral stage ?
Climax community
What are the features of a climax community ?
- Stable state
- Very few dominant plant and animal species
- Which species make up the community depends on the climate
How biodiverse is the climax community ?
It is not that biodiverse
Why is the climax community not that biodiverse ?
Dominant species outcompeting pioneer and other species, resulting in their elimination
When is biodiversity at its highest ?
Mid-succession
What are primary consumers in animal succession ?
- Insects and worms
- They are the first to colonise an area as they consume and shelter in the mosses present
When do secondary consumers arrive ?
When a suitable food source has been established and the existing plant cover will provide them with suitable habitats
When a suitable food source has been established and the existing plant cover will provide them with suitable habitats
The animals have to move in from neighbouring communities
What is it called when succession is stopped artificially ?
Plagioclimax
Who stops succession artificially ?
Humans
What is one of the main reasons deflected succession occurs ?
Agriculture
Give some examples of agriculture causing deflected succession
- Grazing and trampling of vegetation by domesticated animals
- Removing existing vegetation to plant crops
- Burning as a means of forest clearance
Why do scientists measure the distribution and abundance of organisms ?
This is a way of measuring and observing the biodiversity present within an ecosystem
What does the distribution of organisms refer to ?
Where individual organisms are found within an organism
What is the distribution of organisms like ?
Usually uneven throughout an ecosystem
Where are organisms generally found ?
- Where abiotic and biotic factors favour them
- Therefore, their survival rate is high as all the resources they need to live are available to them and selection pressures are low
How do you normally measure the distribution of organisms ?
A line or belt transect is normally involved
What does a line transect involve ?
Laying a line or surveyor tape along the ground and taking samples at regular intervals
What does a belt transect involve ?
Two parallel lines are marked and samples are taken of the area between these two specified points
What types of sampling are transects ?
Systematic sampling
What does the abundance of organisms refer to ?
The number of individuals of a species present in an area at any given time
What does immigration and births cause ?
Increase the number of individuals
What does emigration and deaths cause ?
Decrease the number of individuals
What is a population ?
A group of similar organisms living in a given area at a given time
Can populations be counted accurately ?
No
Why cant populations be counted accurately ?
- Some animals may elude capture
- It may be too time consuming
- Process could damage the environment
How can you increase the accuracy of a sample ?
- Use as large a sample size as possible
- The greater the number of individuals studied, the lower the probability that chance will influence the result
How can you reduce the effect of sampling bias ?
Use random sampling
How do you measure the abundance of plants ?
- Use quadrats
- The abundance of the organisms in that area is measured by counting the number of individual plants contained within the quadrat
What is used to measure animal abundance ?
Capture-mark-release-capture technique
What is the capture-mark-release-capture technique ?
- Capture as many individuals as possible in a sample area
- Mark or tag each individual
- Release the marked animals back into the sample area and follow time for them to redistribute themselves throughout the habitat
- Recapture as many individuals as possible in the original sample area
- Record the number of marked and unmarked individuals present in the sample (release all individuals back into their habitat)
- Use the Lincoln index to estimate the population size
