1. Ecology
Peter Williams

2. Energy Transfer
Energy is transferred down through the ecosystem (organisms living in a particular area).
→ The main way energy enters an ecosystem is through photosynthesis, plants convert UV light energy into a form that can be used by other organisms and store it (biomass). Plants are called producers as they produce organic molecules that are useful for other organisms, through sunlight
Energy is then passed through the ecosystem in stages (food chains), when animals eat other animals:
1.Producer creates energy from UV light
2.Primary consumer consumes producer
3.Secondary consumer consumers primary consumer
4.Tertiary consumer
5.Decomposers recycle uneaten waste products back into the ecosystem
→ Not all energy is taken in from sources, e.g plants can only take in certain wavelengths, animals can only digest some materials. Around 90% of total available energy is actually lost.

3. Calculating energy transfer
Energy between trophic levels can be calculated:
Net Productivity= gross productivity - respiratory loss
% efficiency of energy transfer between trophic levels = net productivity of a level/net productivity of previous level X100
Primary Productivity can also be calculated (talking about primary producers):
net primary productivity = gross primary productivity - plant respiration
NPP=GPP-plant respiration
Net primary productivity is the difference between the energy the producer takes in and the energy the producer uses as resources (e.g to grow). The energy left over is the amount of energy that the primary producer can pass onto the next trophic level.

4. Factors affecting abundance and distribution
Definitions:
→ Habitat: The place an organism lives
→ Populations: All the organisms of a species living within the habitat
→ Populations size/ Abundance: The number of individuals of a species living in a particular area
→ Community: Populations of different species within a habitat
→ Abiotic factors: Non-living features of an ecosystem (weather/available water)
→ Biotic factors: Living features of an ecosystem (predators/available food)
→ Distribution: What part the species occupies of a particular area
Population Size/abundance varies due to abiotic factors and biotic factors:
Abiotic factors:
→ When abiotic conditions are ideal for a species, the organism may grow fast and reproduce successfully
→ e.g when the temperature is ideal for a mammal to live in, the metabolic reactions take place without needing to waste energy on maintaining the internal body temperature. This means the energy can be used for other things like growth and reproduction, increasing population size
→ When abiotic conditions are not ideal for a species, the organism cannot grow as fast or reproduce as successfully
→ e.g when the external temperature is significantly lower than the mammals internal body temperature, energy will be wasted maintaining the body temperature. This means energy that could have been used for growth and reproduction is used up to maintain the optimum temperature to survive. Therefore the organism does not grow as fast or reproduce very successfully, decreasing population size

5. Factors affecting abundance and distribution
Biotic factors:
1. Interspecific competition (competition between different species)
→ e.g red and grey squirrels compete for the same food and habitats
→ This reduces resources available for both species, they will have less energy for growth and reproduction, so the population sizes for both species will be lower than they could be if there was only one of the species living in that area
2. Intraspecific competition (competition within a species)
→ The limit within species is different than 2 species competing against each other. The species population increases with the resources; when resources are plentiful, species population increases. When resources are limited, the species population decreases.
→ When the species population declines, there is a lower species population. This means less competition for food and habitat, which makes better reproduction and growth, causing species population to rise again
→ The species population can only rise to the carrying capacity, the maximum species population that the habitat can support.

6. Factors affecting abundance and distribution
3. Predation (predator and prey populations are linked)
→ As predator size increases, there becomes less food available for the predators, the predator size then begins to decrease
→ As predator size decreases, the prey size increases so there is more food available, the predator size then begins to increase
Distribution varies because of abiotic and biotic factors:
Abiotic:
→ Plants may grow in certain parts (e.g south-facing slopes) for the greatest light intensity
→ Plants may not grow near shoreline because the soil is too saline (salty)
→ Large trees don’t grow in polar regions because temperature is too low
Biotic:
→ A species may be forced out of the habitat because of interspecific competition. If a better adapted species moves into the habitat, it will out-compete the less well-adapted species and therefore will not be able to exist alongside the better-adapted species.
→ e.g the grey squirrel out-competes the red squirrel as it can store more fat over winter and therefore has a better chance of survival
Niche:
→ Every species occupies a niche. This is the role of the species within the habitat:
→ Biotic interactions: what it eats/eaten by
→ Abiotic interactions: oxygen it breathes/ CO2 it breathes out
→ A niche may only be occupied by a single species
→ The abundance of different species may be explained by the niche concept. Species that occupy similar niches may compete for the same food supply, meaning both species will live there, but with a smaller species populations of both species
→ The distribution of different species may also be explained by this concept, a species may only exist where the conditions that make up their niche role also exist. (a pigeon could not exist in a desert because there is different food that it does not eat there)

7. Investigating populations and abiotic factors
→ Abundance/population size (number of individuals of a particular species in a particular area) is measured by taking samples and counting the individuals in the sample taken.
→ Percentage cover can also measure abundance, this is how much of the area is being investigated that is occupied by a species
→ Distribution- where a particular a particular species is within the are being investigated
Random sampling
→ Sample area is a small area within the area being investigated
→ Samples should be taken at random to avoid bias (e.g dividing the area into grids and using a random number generator to pick the area to sample)
→ Using the appropriate technique to take the sample from the chosen sample area
→ Taking as many samples as possible will make the process more reliable as it gives a better estimate for the whole area
→ The populations size of the area can be estimated by taking an average of the data collected in each sample and multiplying by size of the whole area
Sampling techniques
Frame quadrats
→ Used to investigate plant populations
→ Square frame divided into 100 smaller squares by strings across the frame
→ This frame is placed on the random sample area which is taken by random sampling of the area
→ The population size of the species is recorded in each quadrat
→ The percentage cover of a species of plant can be measured by counting how much of the quadrat is covered by the species (count a square if it is more than half covered)
→ Frame quadrats are a quick method of investigating areas with species that fit within a small quadrat (1m x 1m)
→ Areas with large plants and trees need very big quadrats, which are normally marked with tape, without a frame

8. Investigating populations and abiotic factors
Point quadrats
→ Used to investigate plant populations
→ Is a horizontal bar on two legs with a series of holes at set intervals
→ Placed on ground at random points within the area being investigated
→ Pins are dropped through holes in frame and every plant that touches the pin is recorded, if pin touches overlapping plants, all the plants are recorded
→ The numbers of individuals within a species is recorded in each quadrat
→ Percentage cover can also be measured by calculating number of times a pin touched a species as a % of the total pins dropped
→ Point quadrats are useful in areas where there is lots of dense vegetation close to the ground
Transects
→ Used to investigate distribution of plant populations
→ We can use transects to find out how plants are distributed across an area, for example how the species population changes from hedge to a field
1. Line transects- A tape measure is placed along the transect and the species that touch the tape are recorded
2. Belt transects- Data is collected along the transect using frame quadrats placed next to eachother
3. Interrupted transects- Instead of investigating the whole transect of either a line or belt, we can take measurements at intervals (e.g placing point quadrats at right angles to the direction of the transect at set interval like every 2 meters)

9. Investigating populations and abiotic factors
Measuring abiotic factors
Climate
→ Temperature- Thermometer
→ Rainfall- Rain Gauge, a funnel attached to a measuring cylinder. Rain falls down funnel into cylinder, allowing us to measure volume of water collected over a period of time
→ Humidity- Hygrometer (measures amount of water vapour in air)
Oxygen availability
→ Oxygen sensor measures the amount of oxygen that is dissolved in the water (Aquatic habitats)
Solar input
→ Light intensity is measured using a light sensor
Edaphic factors (soil conditions)
→ pH is measured using indicator liquid (sample of soil is mixed with an indicator liquid that changes colour depending on pH. pH probes may also be used)
→ Moisture content is also measured, the mass of the soil is measured before and after drying at 100oC. The difference in mass is calculated in a % of the original mass, showing water content
Topography (shape and features of earth surface)
→ Relief (how height of land changes across a surface) is measured using a GPS device at different points across the surface.
→ Slope angle (measured using clinometer)
→ Aspect (direction slope is facing is measured using a compass)

10. Succession
Succession is the process in which the ecosystem changes over time, this includes biotic condition (animals & plants) and abiotic conditions (resources, temperature etc.)
Primary succession
→ Occurs on newly formed land, for example a volcano explosion that has no organic material, just rock
Secondary succession
→ Happens on a land that has been cleared of all plants, but some organic material may remain , for example after a forest fire
Seral stages
1. Primary succession occurs when a species colonise a new land surface
→ The first species to colonise the area are called the pioneer species
→ The abiotic conditions are harsh, there is no soil to retain water. Only the pioneer species may grow because they are specialised to cope with the harsh conditions
→ The pioneer species change the abiotic conditions , as the pioneer species die, microorganisms decompose the dead matter into basic soil
→ The conditions are now less hostile (e.g basic soil may retain water), other organisms may now live in these conditions and move in. As these new species die, they add more organic material into the soil, meaning the soil can retain even more water
2. Secondary succession occurs
→ As there is already a soil layer, organisms take advantage, the soil layer allows bigger plants to move into the area and out-compete the original pioneer species. The new species become the dominant species in the ecosystem
→ As succession carries on, the ecosystem becomes more complex, the species diversity increases
3. Climax community
→ The ecosystem reaches a steady state, it is supporting the largest and most complex community of plants and animals it can and won’t change much more
Preventing succession
→ Stopping the normal climax community within that ecosystem can be prevented, when it is prevented, it is called a plagioclimax
→ Cutting the grass is preventing bigger plants like bushes and trees growing, larger plants cannot establish themselves and therefore the climax community consists of mainly grass.