18.6 The Impact of Change

A free GCSE Biology lesson for AQA (8461) from OBA School: how changes in temperature, water and atmospheric gases affect where species live. Watch the video, read the explanation and worked examples, then try the revision questions. You can work through the full lesson, with every video, practice quizzes and printable worksheets with mark schemes, in our free online course.

What you will learn

• Explain how changes in temperature, water availability and atmospheric gases affect the distribution of species
• Describe changes that are seasonal, geographic or caused by human interaction, with examples
• Interpret data showing changes in the distribution of a species
• Evaluate whether data supports a conclusion about environmental change

Key words

• Distribution: Where a species is found, and how widely it is spread across an area.
• Environ- mental change: A change in the abiotic (non-living) conditions of a habitat, e.g. temperature or water.
• Seasonal change: A change that happens each year with the seasons, such as cold winters or dry summers.
• Geographic change: A difference in conditions from place to place, e.g. with latitude, altitude or distance from the sea.
• Migration: The regular movement of animals from one area to another, often with the seasons.

What changes the distribution of species?

Every species is adapted to a particular range of conditions. If the environment changes, a species may move to a new area, spread further, or disappear from an area. The main changes are:

• Temperature; Examples of how it affects distribution Warmer conditions let some species spread towards the poles or up mountains. Species that need cold conditions lose habitat.
• Availability of water; Examples of how it affects distribution Droughts or draining of wetlands remove habitats of water-loving species. Floods or wetter climates favour others.
• Composition of atmospheric gases; Examples of how it affects distribution Sulfur dioxide pollution kills many lichens, so fewer lichen species grow near polluted areas. More CO₂ in sea water makes it more acidic, harming corals and shellfish.

Seasonal, geographic and human changes

• Seasonal; Example Many birds migrate south in autumn because temperatures fall and their food (e.g. flying insects) becomes scarce. They return in spring.
• Geographic; Example Different plants grow at the top of a mountain from at the bottom, because it is colder and windier higher up.
• Human interaction; Example Global warming, draining wetlands for farmland, building dams, and air pollution all change conditions, so species move or die out.

Worked example: rate of change uphill

The lowest altitude at which an alpine plant grew was 820 m in 1980 and 905 m in 2020.
Change = 905 − 820 = 85 m in 40 years
Mean rate = 85 ÷ 40 = 2.1 m per year (2 s.f.)

Answer: the plant’s lower limit moved up by about 2.1 m per year

Using data about distribution

Fewer lichen species grow near the city centre. Many lichens are killed by sulfur dioxide, and the air near the centre is likely to contain more of it from traffic and heating. Lichens are useful because their distribution shows the composition of the air.

Exam tip: When you explain a change in distribution, name the environmental factor (temperature, water or gases), say whether the change is seasonal, geographic or human, and explain why the species can or cannot survive there.

When evaluating a conclusion, check: is there enough data, over a long enough time? Could another factor (for example, a new food source or less pollution) explain the change? A correlation does not prove one factor caused the change.

Common mistakes

• Saying animals “decide” to move because they want to. Explain that individuals survive and breed only where conditions suit them, so the distribution changes.
• Forgetting the third factor: the composition of atmospheric gases (e.g. sulfur dioxide or CO₂), not just temperature and water.
• Claiming one set of data proves global warming caused a change. Other factors could be involved, so say the data supports or suggests a link.
• Mixing up seasonal changes (every year) with long-term changes such as climate change.

Revision questions

Try these, then check your answers below each one.

Question 1. Which list contains only environmental (abiotic) changes that can affect where species live? (Choose from: New pathogens, rainfall, number of prey, Temperature, availability of water, composition of atmospheric gases, Temperature, new predators, new diseases, Food supply, competition, availability of water.)

Answer: Temperature, availability of water, composition of atmospheric gases

Working: The three environmental changes in the specification are temperature, water availability and the composition of atmospheric gases.

Question 2. True or false? Finding fewer lichen species near a busy city centre suggests that the air there contains more sulfur dioxide.

Answer: True

Working: True. Lichen distribution reflects the composition of the air.

Question 3. The lowest altitude at which a mountain plant grows rose from 760 m to 880 m over 40 years. Calculate the mean rate at which it moved uphill.

Answer: 3 m per year

Working: 880 − 760 = 120 m. 120 ÷ 40 = 3 m per year.

Related lessons

• Previous lesson: 18.5 Global Warming
• Next lesson: 18.7 Maintaining Biodiversity
• In this chapter: 18.1 The Human Population Explosion
• In this chapter: 18.2 Land and Water Pollution
• In this chapter: 18.3 Air Pollution

Continue in the full course

This lesson is section 18.6 (AGCBH1806) of our free GCSE Biology course for AQA. In the full course you get every video for this section, a self-marking practice quiz, a printable worksheet with a mark scheme, chapter tests, and your progress saved. Go to the full GCSE Biology course.