Fieldwork and competition (CCEA)

• Biodiversity: a measure of the number of different species living in an area.

• Population: the number of organisms of the same species living in an area.

• Habitat: where a population lives.

• Environment: an organism’s surroundings. It contains factors that influence the organism. These factors can be divided into abiotic and biotic factors.

• Abiotic non-living factors eg temperature.

• Biotic: living factors eg a predator.

• Community: several populations of different species living in habitats close together.

• Ecosystem: an area where a community of organisms live and are affected by a range of environmental factors.

The distribution of organisms in a habitat can be affected by abiotic factors such as temperature and light.

Counting all organisms in a large area is often difficult due to time limits and because animals may hide.

To address this, small sections within the larger area are sampled.

Effective sampling should be:

reliable, a large sample size is needed – 20 to 30 quadrats counted.

representative of the habitat being investigated. Quadrats should be placed randomly to produce valid results and avoid bias.

Quadrats are a small square frame that can be used to investigate the abundance of plants and non-motile animals in a habitat.

Procedure

1. Place two measuring tapes at right angles to create a co-ordinate grid.
2. Use a random number generator to make random coordinates.
3. Place a quadrat at each coordinate.
4. Count the numbers of each species in each quadrat.
5. Use a key to identify unknown species.
6. Record results in a table.
7. Calculate the average of each species per quadrat.
8. Multiply the average by the total area to estimate the population size of each species in the habitat.

The belt transect is used to study changes across a habitat.

Procedure

1. Place a measuring tape (10m) across the habitat.
2. Place a quadrat at regular intervals (eg every 1 m) along the transect line.
3. Count the numbers of each species.
4. Record results in a table.
5. Repeat step 2-4 to get reliable results.
6. Calculate the average number of each species at each interval.
7. Plot results on a bar graph.

Results

Conclusion:

The number of sea lettuce and barnacles decrease with increasing distance from the shoreline whereas the number of sea anemones increase because there are different conditions at various distances from the shore.

An organism’s surroundings (abiotic and biotic factors) can influence its distribution.

Biodiversity is measured by using quadrats and belt transects.

Other plants and animals can affect the distribution of an organism.

Biotic factors, like predation and competition, strongly influence species distribution. For example, high predator numbers can reduce prey populations, while limited food resources can heighten competition and impact survival.

Biotic factors are much more difficult to measure than abiotic.

Competition between animals is usually for:

• food
• water
• territory
• mates

Competition between plants is usually for:

• light
• water
• minerals
• space

Competition for these resources can affect population growth.

Organisms have adapted to their individual environments and to any competition for resources.

Human effect on the ecosystem

Humans can also influence the normal balance of an ecosystem.

Humans disrupt ecosystem balance through activities such as:

• deforestation
• pollution
• overfishing
• climate change

These actions alter habitats, reduce biodiversity and destabilise food webs, impacting the health and endangering species.

Red and grey squirrels

The grey squirrel is not native to the UK - it was introduced from North America.

There is great competition between the red and grey squirrel with the population of the grey outweighing that of the red in some areas.

This has happened for a number of reasons.

• The grey squirrel eats a wider range of food and can survive in areas of mixed woodland whilst the red squirrel cannot.

• The grey squirrel carries a disease that is fatal to red squirrels while the grey remains unaffected.

However, grey squirrels are much larger than red squirrels and need more food to survive.

In areas where seeds are small (eg conifer forests) the grey squirrel struggles to obtain enough food and the red squirrel dominates.