Ecosystem - an ecological unit which includes all organisms living in a particular area and all of the ABIOTIC factors (non-living) in a local environment.
Population - all the individuals of a givenspecies in a particular area.
Community - all the living organisms in an ecosystem.
all interconnected by food chains and food webs.
Habitat - the place where the communities live e.g. a field, rocky shore.
Niche - the "role" of an organism - where it lives, what it eats and when, when it is active etc. Each species has it's own unique niche.
Environment - conditions surrounding an organism. Includes both BIOTIC (competition & predation) and ABIOTIC factors (temperature, rain fall).
Energy Flow in Ecosystems
Energy originates from LIGHT and is fixed into the ecosystem through PHOTOSYNTHESIS.
The energy stored in plants is then passed onto organisms along food chains.
Sun (provides energy, not part of food chain) > producer > primary consumer > secondary consumer > tertiary consumer
At each trophic level, approx. 10% of the energy is used for growth and storage - which is the energy that can be passed on to the next tropic level, when the organism is consumed.
-> 90% is wasted between one trophic level to the next. E.g. 100kJ > 10kJ > 1kJ > 0.1kJ
Food-in (100% energy) > feces, urine, gas 60% > respiration 30% = energy that is stored or used for growth 10% - passed on.
Food Chain: Pyramids
- easy to produce
- misleading - shape can become inverted if there are small numbers of big organisms (a tree) or big numbers of small organisms (parasites).
- measuring biomass (dry mass) of organisms kg/m(squared).
- difficult to measure (need to kill organism) = unethical
- almost always pyramid-shaped
- measures amount of energy (kJm(squared)/yr(minus 1)
- difficult to measure
- always pyramid-shaped
Air & Water
V /\ /\
PHOTOSYNTHESIS RESPIRATION COMBUSTION
V ----------------/\ /\ /\-----------------
PLANTS > ANIMALS DECOMPOSERS mushroom
V V V /\
DEATH AND DECAY ----------------
Fossil Fuels ------------------- /\ (to COMBUSTION)
Important Features of Carbon Cycle
1) CARBON gets to ecosystems through PHOTOSYNTHESIS
2) How different eaters get carbon..
- Herbivores eat plants
- Carnivores eat other animals
- Omnivores eat a mixture of the two
3) Decomposers get carbon by digesting dead organisms - known as saprotrohic nutrition.
4) All living organisms return carbon to the air in the form of carbon dioxide, through respiration.
5) When plants / animals are not decomposed, they get turned into fossil fuels over millions of years.
6) Carbon in fossil fuels is released when they are burned - COMBUSTION.
7) Microorganisms are important in the cycle because they return carbon from dead material into the atmosphere.
Constant Atmospheric Carbon Dioxide Levels
- only in natural situations does the carbon cycle keep carbon dioxide levels more or less the same.
Human activity is affecting the global carbon balance in two ways:
1) burning of huge quantities of wood and fossil fuels
- adding CO2 into the air!
2) clearing large areas of forest (deforestation), which normally absorbs some of the carbon in the atmosphere.
> In combination, the total amount of carbon dioxide is much higher than it naturally would be.
Nitrogen Cycle is essential as 78% of atmospheric air is nitrogen.
- Nitrogen is needed by animals and plants for proteins and nucleic acids
- Bacteria is ESSENTIAL
1) Atmospheric nitrogen is fixed by bacteria. The bacteria lives free in the soil or in the root nodules of leguminous plants. The atmospheric nitrogen is converted into ammonia and then into amino acids by the bacteria.
Atmospheric nitrogen > Ammonia > Amino Acids
2) The protein (amino acids) in plants is passed along the food chain.
3) When living organisms die, microorganisms return nitrogen to the soil in the form of ammonium compounds.
Animals get rid of excess amino acids by deamination, and nitrogen is return to the soil via urine.
4) Ammonium compounds are converted back into nitrates by nitrifying bacteria.
Ammonium compounds > nitrites > nitrates
5) Nitrates converted back into atmospheric nitrogen by DENITRIFYING BACTERIA.
Other processes may be included on exam diagrams
1) Haber Process - converts atmospheric nitrogen > nitrate fertilisers + ammonia
2) Lightening - nitrogen > nitrites
Taking Abiotic Measurements:
Temperature - use a thermometer
pH -only taken for soil / water. Indicator paper / liquid or an electronic pH monitor
Light Intensity - difficult because of variation. Connect a light sensor to a data logger and take readings over a period of time
Oxygen - only in aquatic habitats. Use an Oxygen Electrode to take readings
Air Humidity - measured with a hygrometer
Moisture Content - of the soil is calculated.
1) Find the mass of a soil sample
2) Put in the oven and dry out
3) Work out mass lost, worked as a percentage (%) of original mass
E.g. Soil Sample - 100kG
Dry Sample - 50kG = 50%
Studying Ecology - Quadrat Frames
Three Key Factors when working out diversities:
1) Species Frequency - how abundant a species are
2) Species Richness - the total number of different species in an area
3) Percentage Cover - how much of the surface is covered by a particular plant species (cannot be used for animals because they move too much!)
> To measure all of these, use a frame quadrat - area inside is a quadrat
Quadrat frames are laid on ground (river, sea, pond bed if it's aquatic environment). The total number of species as well as the number of individuals of each species.
Sampling method - unpractical to cover whole area! The data from sample is then used to calculate figures for the entire area. Random sampling is used to ensure there is no bias data.
Studying Ecology - Quadrat Frames
Species frequency is calculated by counting how many quadrats each species appears in and is given as a percentage. E.g. if a species was found in 5/20 quadrats, it's frequency would be 25%.
Species richness is measured by counting the total number of species found in all samples. Assume this is same number for entire area.
Percentage cover is measured dividing the area inside the quadrat frame into a 10x10 grid and counting how many squares each species takes up. Plants can overlap - so the total can be over 100%.
Important to take random samples and the size of the quadrat - smaller quadrats are more accurate, but they take longer to collect data and are inappropriate for large plants + trees.
Plotting a graph of cumulative species number found against a number of quadrats sampled should show how many quadrats you need to sample in further studies of the same habitat.
Pins are dropped through the holes in the frame and each plant a pin hits is recorded. If several plants are hit by one pin, all of them are recorded.
A tape measure is laid along the area you want to study and quadrat is placed at regular intervals (every 2 meters) at a right angle to the tape.
Line & Belt Transects
Line of sample is called a transect. When you want to look at trends in an area e.g. the distribution of a species.
LINE - place a tape measure along the transect and record what species are touching the tape
BELT - data collected between TWO TRANSECTS a short distance apart. Done by placing framed quadrats along the transect.
Sampling MUST be random - it's important that the sample accurately represents the ecosystem as a whole.
This can be done by picking sites randomly - divide whole area onto a grid and use a random number generator to select each co-ordinate.
****NEED TO LOOK AT DATA HANDLING AND FORMULAS FOR THIS SECTION
- SEE PAGE 54 & 55
Dynamics of Ecosystems
Population growth is stopped by limiting factors
Limiting factors put an upper limit on a population's size.
Many limiting factors are abiotic - e.g. temperature, soil, or water pH
Some of these things, can affect the RATE of POPULATION GROWTH as well as limiting the total size.
Interactions between organisms can limit the population size
Two important interactions: competition and predation
1) Competition occurs when a lot of organisms are competing for some sort of limited resource - often food, but can be shelter, nesting sites and mates.
2) If the organism are the same species, it is called INTRASPECIFIC COMPETITION. If they are from different species, it is called INTERSPECIFIC COMPETITION.
INTERSPECIFIC COMPETITION affects the population distribution
Sometimes, interspecific competition can prevent a species from living in an area at all.
E.g. since the introduction of the grey squirrel, the native red squirrel has disappeared from areas because of interspecific competition. In the few areas where both live, both populations are smaller than they would be if there was only one kind of squirrel there.
Intraspecific competition happens between members of the same species in a population.
As the population grows there will be more competition for FOOD and SPACE.
The population grows until some factor becomes limiting, and then it will begin to decline. A smaller population means there is less competition for space and food, which is better for survival and reproduction - so the population grows again.
The population varies around an average figure - carrying capacity.
Predator and Prey populations are interlinked
The presence of predators affects the size of populations.
*When there is a graph showing a predator / prey population - REMEMBER
1) The theory is that as the population of the prey grows, there is more food for predators and so the predator population grows.
2) As the predator population gets larger, more prey are eaten so the prey population falls.
3) There is then less food for the predators so the population of predators go down.
> You rarely get this exact pattern, because it's unusual to get a situation where a species is eaten by just one predator or a predator eats just one prey.
Before now, the factors discussed have been density dependent - have a greater impact as the population gets more dense. E.g. disease.
Some other factors, flooding and forest fires are density independent - they can affect populations of any density. The factors are completely unrelated to population density.
Succession is the process where plant communities gradually develop on bare land. Eventually, a stable climax community develops and after that, big changes don't tend to happen.
Two types of Succession:
Primary Succession - happens on land where there is no proper soil and no living organisms. New land created by volcanic eruption is a good example of where a primary succession will occur.
Secondary Succession - happens when most of the living organisms in an area are destroyed, but the soil and some living organisms remain.
E.g. woodland that has been burned down by a forest fire, areas subject to severe pollution, or land that is cleared for housing or new roads.
Each stage is known as a seral stage
> in each stage: the plants change the environmental conditions and make them suitable for the next plants to move in.
You need to know an example of succession
bare sand dunes > mature woodland
marram grass > grass community > shrub community > tree community
1) The first "poineer" species to colonize the area need to be able to cope with harsh abiotic conditions on the sand dunes - little / no freshwater available, high salt levels, the wind is strong and there is no proper soil.
- Marram grass is ideal - good xerophytic adaptations
2) As pioneer species die, they are broken down by microorganisms. The dead marram grass adds organic material to the sand creating a very basic "soil", which can hold more water than plain sand.
3) The soil means that abiotic conditions are less hostile and so other, less specialised grasses begin to grow. These eventually out-compete the original colonisers via interspecific competition.
4) As each new species moves in, more niches are created and the area is more suitable for more species.
5) After the grass communities have been out-competed, the area will be colonised by shrubs e.g. brambles.
6) Eventually, the area becomes dominated by trees. The trees dominate because they create a canopy - preventing light from reaching herbaceous plants.
Diversity INCREASES and Species CHANGE as succession progresses:
Pattern of Change:
- species present become more complex
- total number of organisms increases
- number of species increases
- larger species of plants arrive
- animals begins to move into the area - each seral stage, larger animals move in
- food webs become more complex
- these changes all mean the ecosystem becomes more stable
Different Types of Climax Community
Various factors can stop succession going any further and lead to a climax community. - Climax is classified based on what caused the succession to stop.
1) Climatic Climax - succession has gone as far as the climate will allow. E.g. trees cannot grow at high altitudes, so the largest plants are shrubs.
2) Human activities - stop succession by felling trees / ploughing fields / grazing animals on farm land. Some ecosystems are deliberately "managed" to keep them in a particular state. When succession is stopped artificially, it's called a PLAGIOCLIMAX. E.g. farmland, if upkeep stopped, it would develop into a woodland.