Biotic and abiotic factors

Biotic factors include anything which comes from the activity of any living thing.

Examples of biotic factors are

• grazing
• predation
• competition for resources
• disease
• food availability

Abiotic factors are all the ones which do not come from living things.

Examples of abiotic factors are

• pH
• temperature
• light intensity
• moisture

Measuring abiotic actors

The main abiotic factors which you need to know are light intensity, temperature, pH and soil moisture.

Each of these factors can easily be measured using suitable meters.

• temperature using thermometer or temperature probes
• light using light meters
• moisture using moisture meters
• pH using pH meters or chemical test.

The rules for ensuring representative and reliable values are always the same.

• Take several readings to minimise the effect of odd readings and possible errors.
• Make sure that your sample is representative by including as much of the area as possible.

Keep errors to a minimum with an organised approach and attention to detail.

• For example, keeping your instruments (especially the probes that do the actual measuring) clean and free from contamination.
• Take careful and clear notes for every measurement you make.
• When measuring light intensity, you want to know which plants are in shade and which are in full sun, so measure in shaded areas as well as open ones.
• Make sure that the shade is natural and not from your own shadow!

Quadrats

Quadrats are good for sampling plants and slow moving animals.

The main sources of error involve your sample being either unreliable or unrepresentative.

Unreliable samples can be improved by taking a bigger This could be done by examining more quadrats or using bigger quadrats.

Unrepresentative samples mean that the quadrats have not covered the area to include any different zones which exist, or that the quadrats have been put down in a biased way (such as putting them in areas with pretty flowers!

This can be improved by random sampling, or by spreading the quadrats out to a prearranged plan.

Pitfall Traps

A pitfall trap is a smooth sided container sunk into the soil so that small ground living invertebrates fall in.

This allows us to note what species are living in the area.

Pitfall traps are no use for sampling larger animals, or those that can fly.

The main sources of error include bad sampling as with any technique.

• The trap needs to be exactly level with the ground so that animals can fall in.
• The sides need to be steep and smooth so that they can’t climb out again.

There must be no spaces between the trap and the soil for invertebrates to fall into and so miss our trap.

The trap needs a cover to keep out rain and prevent birds from eating our sample.

The cover needs to be far enough above the trap to leave space for the animals to get in.

It should have some small drainage holes in the bottom to allow water to escape.

Using and constructing paired-statement keys to identify organisms

A paired-statement key looks like the one below. Each feature is dealt with by a paired-statement which ether identifies the organism or sends you to another paired-statement to help identify the organism by another feature.

In this example, colour has been done in statement 1. So statement 2 only includes green coloured seaweed. The feature here is shape and the blank identifies Cladophora, so the blank should be long and thin. Statement 4 refers to the bladders feature, along its length, so that refers to egg wrack only. Finally, statement 5 refers to shape, specifically branched. You have already identified egg wrack, therefore the answer must be Bladder Wrack.

Biodiversity

• Biodiversity is a way of describing the variety of living things in an area.
• Biotic factors and abiotic factors control the biodiversity in an ecosystem.
• Human activities can also have a big impact on biodiversity.

A range of human influences that affect environments:

• pollution of air and water
• habitat destruction by
  • deforestation (tropical rain forest)
  • desertification
  • overfishing

Indicator Species

Indicator species are species that by their presence or absence indicate environmental quality/levels of pollution.

eg. Lichen, water creatures.

Topic Summary