Impact of Environmental Change (HT + biology only)

SPEC 4.7.2.4 • PAPER 2

BIOLOGY ONLY (8461)

HIGHER TIER ONLY

Impact of Environmental Change

How temperature, water and atmospheric gases shift species distribution — and how to evaluate the impact when AQA hands you a graph or scenario.

The Big Idea

This lesson is about distribution — where species live — and how environmental changes shift it. AQA tests this with data: you'll get a graph, table or scenario, and your job is to evaluate the impact.

Key Term

Distribution = where in the environment a species is found (geographic range, habitat, depth, altitude). Not the same as population size.

Spec Statement

"Students should be able to evaluate the impact of environmental changes on the distribution of species in an ecosystem given appropriate information ."

Biology Only + Higher Tier Only

Section 4.7.2.4 appears only on GCSE Biology Paper 2 Higher tier (8461/2H). Not in Combined Science; not in Foundation tier.

The Three Named Changes

The spec lists exactly three types of environmental change. Memorise them — they're often the first 1–2 mark points in any question on this topic.

1 — Temperature

Air, water and soil temperatures shift species ranges (latitude / altitude / depth).

2 — Availability of Water

Rainfall, soil moisture, surface water, groundwater. Drought or flooding shifts which species can live where.

3 — Composition of Atmospheric Gases

CO₂, O₂ (in water bodies), pollutant gases (e.g. SO₂). Affects photosynthesis, respiration, and sensitive species.

Watch The Wording

The spec says "availability of water" — not just "water". Don't write "water increases" — write "availability of water decreases/increases" or use a specific change like "rainfall falls" or "drought".

Three Sources Of Change

The spec also lists three causes. Mark schemes often expect students to identify which source applies in a given scenario.

SourceExamplesDistribution Effect

SeasonalAnnual temperature cycles, monsoons, dry/wet seasonsMigration; species numbers rise and fall through the year (e.g. summer visitors)

GeographicDifferences with latitude, altitude, distance from coastWhy species are found in some regions and not others (e.g. polar vs tropical)

Caused by human interactionClimate change, deforestation, pollution, draining wetlands, urbanisationHabitat loss/shift; rapid changes that species may not adapt to in time

Common Trap

Students often default to "humans cause it". But seasonal and geographic changes are also valid spec answers. Read the question — if a graph shows species numbers across a year, it's likely seasonal; if it compares altitudes, it's geographic.

Change 1: Temperature

Most species have a narrow temperature range they can survive in. When average temperature shifts, species ranges shift too.

Key Effects On Distribution

Cold-adapted species (alpine, polar) shift poleward or to higher altitude — habitat shrinks.

Warm-adapted species can expand their range into newly suitable areas.

If species cannot disperse fast enough (e.g. plants, isolated populations), their distribution shrinks and they may go locally extinct.

Change 2: Availability of Water

Less Water Available

Drought reduces rainfall and soil moisture.

Wetlands shrink or dry out.

Rivers and lakes drop in level.

Distribution shifts: drought-tolerant species (e.g. succulents, deep-rooted grasses) expand; moisture-dependent species (e.g. amphibians, ferns) decline.

More Water / Flooding

Heavy rainfall or sea-level rise floods habitats.

Soil becomes waterlogged → low oxygen for roots.

Aquatic species can expand into newly flooded areas.

Terrestrial species adapted to drier conditions may be displaced.

Synoptic Link

Water availability is an abiotic factor from lesson 7.01 (spec 4.7.1.2). Knowing the abiotic factor framework helps you write specific answers — "moisture level decreases" beats "less water".

Change 3: Composition of Atmospheric Gases

Changes in the gases in air (or dissolved in water) directly affect species that depend on or are sensitive to them.

Gas ChangeEffect On Species Distribution

↑ CO₂ (from burning fossil fuels)Direct: plants may grow faster (more raw material for photosynthesis). Indirect: drives global warming → temperature effects on cold-adapted species. Oceans absorb more CO₂ → ocean acidification → harms shellfish, coral and other calcifying species.

↑ Methane / other greenhouse gasesPowerful greenhouse gases (e.g. CH₄ from livestock, landfill, melting permafrost). Contribute to atmospheric warming → indirect distribution effects on temperature-sensitive species worldwide.

Pollutant gases (e.g. SO₂, NOₓ from burning fossil fuels)Sensitive species (e.g. lichens) decline or disappear in polluted areas; tolerant species dominate. Lichens are used as bioindicators of air quality. Acid rain (from SO₂ dissolving in rainwater) acidifies lakes → harms fish.

Synoptic Link → Lesson 7.10

The greenhouse-gas mechanism is covered in detail in lesson 7.10 (Global warming, HT only). For 4.7.2.4 questions you just need to know that changes in atmospheric gas composition shift species distributions — directly (e.g. plant growth, lichen tolerance) or indirectly (via warming).

Stay In Scope

The spec for 4.7.2.4 only asks you to recognise that gas composition affects distribution. Detailed pollution mechanisms belong to lesson 7.09 (Waste Management). Note: "oxygen levels in water" is an abiotic factor for aquatic animals (spec 4.7.1.2) — not strictly a change in atmospheric gas composition.

The HT Skill: Evaluate

"Evaluate" is the highest-demand command word for this topic. AQA gives you data (graph, table, scenario) and you must judge the impact — not just describe it.

Four-Step Evaluation Framework

1

Read the data — identify the trend (what's changing, by how much, over what time/place).

2

Link to a named change — temperature, water availability, or atmospheric gases. State which source (seasonal / geographic / human).

3

Predict the distribution effect — which species gain, which lose? Explain mechanism (adaptation, dispersal, tolerance).

4

Reach a judgement — balance impacts. Note uncertainties. Use data from the question to support your conclusion.

"Evaluate" vs Other Verbs

Describe: state the trend (what happened).

Explain: give reasons (why it happened).

Evaluate: weigh up impacts, consider both sides, reach a judgement (so what?).

Worked Example 1: Seasonal Change

A graph shows the number of three bird species in a UK woodland across one year.

Evaluating Using The Framework

Step 1 (Read data): X stays roughly constant year-round; Y peaks in June–July, absent in winter; Z peaks in December–January, low in summer.

Step 2 (Named change/source):Seasonal changes in temperature (and food availability/day length).

Step 3 (Effect): Y migrates IN for warm summer (warm-adapted, food abundant); Z migrates IN for cold winter (cold-adapted, escaping summer heat elsewhere). X tolerates both — resident.

Step 4 (Judgement): Seasonal temperature shifts the distribution of Y and Z in and out of the woodland. X's distribution is unaffected by seasonal change at this site.

Worked Example 2: Human-Caused Change

Scenario: A small lake in a national park has warmed by 1.8 °C over 40 years due to climate change. The lake originally contained a cold-water fish species (the Arctic charr) and a warm-tolerant aquatic insect (the damselfly nymph). Evaluate the likely impact on the distribution of each species.

Model Evaluation

Step 1 — Read the data:

Average temperature has risen by 1.8 °C over 40 years — a sustained, directional change (not seasonal fluctuation).

Step 2 — Identify the change and source:

Change = temperature. Source = human interaction (climate change from greenhouse gases).

Step 3 — Predict the effects:

Arctic charr — adapted to cold water, low temperature tolerance. As the lake warms, its suitable habitat shrinks (perhaps only the deepest, coldest layer remains). Distribution may contract to the lake bottom; if water becomes too warm even there, local extinction is possible.

Damselfly nymph — warm-tolerant. Distribution may expand within the lake as more of the water column becomes suitable. May even spread to lakes that were previously too cold.

Step 4 — Judgement:

The same temperature change has opposite effects on the two species: distribution shrinks for the cold-adapted charr, expands for the warm-tolerant damselfly. The overall impact depends on dispersal ability and whether the charr can survive in remaining cold microhabitats.

Common Errors

Wrong

"Distribution = how many of the species there are."

Right

"Distribution = where the species is found (range, habitat, altitude). Population size is a separate measure."

Wrong

"Temperature rise kills all species."

Right

"Some species gain (warm-adapted expand); others lose (cold-adapted contract). Depends on adaptation and dispersal ability."

Wrong

"Environmental change always means humans."

Right

"Three sources on the spec: seasonal, geographic, and human interaction. Read the data to decide which applies."

Wrong

Describe the graph without evaluating impact.

Right

For "evaluate" questions, go beyond description — link trend to cause, identify winners and losers, reach a judgement.

Wrong

"Species will move to a new habitat."

Right

Many species cannot disperse fast enough (especially plants, isolated populations). Distribution may shrink rather than shift cleanly.

Examiner Alerts

Alert 1 — Use The Data

"Given appropriate information" is in the spec wording. Quote numbers or trends from the data in the question. Generic textbook answers without referring to the data lose marks.

Alert 2 — Distribution ≠ Population

"Distribution" is about location / range. If a question asks about distribution, don't just say numbers go up or down — say where the species is or isn't found.

Alert 3 — Three Named Changes, Three Named Sources

Use the spec terms: temperature, availability of water, composition of atmospheric gases; seasonal, geographic, human interaction. Mark schemes credit these specific terms.

Alert 4 — Balance The Evaluation

"Evaluate" means weigh up. If a change favours one species but harms another, say BOTH. A one-sided answer caps at Level 2.

Practice — Recall

13.1 Name the three types of environmental change that affect the distribution of species, according to the spec. 3 marks

13.2 A scientist observes that a population of mountain hares is found at progressively higher altitudes each decade. Suggest which of the three named changes is most likely responsible. 1 mark

13.3 State whether this change is most likely seasonal, geographic, or caused by human interaction, and justify your answer. 2 marks

13.1

Temperature (1); availability of water (1); composition of atmospheric gases (1).

13.2

Temperature (1) — hares are moving to higher altitudes to find cooler conditions as their original altitude warms.

13.3

Caused by human interaction (1) — the change is sustained and directional over decades, consistent with climate change driven by human activity (1). It is not seasonal (would repeat each year) and not purely geographic (geographic changes don't shift over decades in one direction).

Practice — Evaluate Data

The graph below shows the percentage of pond surface covered by two species of pondweed in a UK pond between 2010 and 2026. Over this period, the annual mean water temperature rose from 11 °C to 13 °C.

Evaluate the impact of the temperature change on the distribution of the two pondweed species. 4 marks

1

Read the data: Species P (native) decreased from ~60 % to ~20 % cover; Species Q (introduced) increased from ~10 % to ~50 % cover. Mean temperature rose by 2 °C. (Mark for using data.)

2

Identify the cause: The change in temperature is the named environmental change; this is likely caused by human interaction (climate change). (1)

3

Predict effects: The native Species P appears to be less tolerant of higher water temperatures — its distribution within the pond contracts. Species Q is warm-tolerant and expands its coverage. (1)

4

Judgement: The temperature rise has had opposite effects on the two species — distribution of P decreased while distribution of Q increased. Note: correlation, not proof of causation — other factors (nutrients, light, competition) could contribute. (1)

Tip: Level 3 answers quote numbers from the graph and acknowledge the limits of the data (e.g. other factors).

Practice — 6-Marker

An upland peat bog in northern England has been monitored for 50 years. During this time, summer rainfall has decreased by 25 % and average summer temperatures have risen by 1.5 °C. The bog supports populations of Sphagnum mosses (water-dependent), a ground-nesting bird species, and a heather plant that tolerates drier conditions.

Evaluate the likely impact of these changes on the distribution of the three species. 6 marks (Level marked)

Level 3 (5–6): coherent evaluation with named changes, named sources, all three species addressed, balanced judgement using data.

A

Identify the changes: two named changes — temperature (up 1.5 °C) and availability of water (rainfall down 25 %). Source: likely caused by human interaction (climate change), sustained over 50 years.

B

Sphagnum mosses: water-dependent. Reduced rainfall lowers the bog's water table; warmer temperatures increase evaporation. Distribution of Sphagnum is likely to shrink — confined to remaining wettest areas or lost entirely.

C

Ground-nesting bird: depends on the bog habitat structure. As Sphagnum declines and bog dries, nesting habitat is degraded. Distribution likely contracts. The bird may also struggle if its food (insects, larvae) declines with the moss.

D

Heather: tolerates drier conditions. As the bog dries, suitable habitat for heather expands across the site. Distribution increases.

E

Judgement: Two changes acting together favour drier-adapted species (heather) at the expense of water-dependent species (Sphagnum) and the bird that depends on the wet bog. Overall biodiversity of the bog community is likely to decrease even if heather expands.

Level 2 answers describe each species without linking explicitly to the named changes. Level 1 answers list facts without judgement.

Recap & Next Up

3

Named changes

3

Sources of change

4

Evaluation steps

Three Things To Take Away

1

Three named changes: temperature, availability of water, composition of atmospheric gases. Three sources: seasonal, geographic, human interaction.

2

Distribution ≠ population. Distribution is about where a species is found. Environmental changes shift it.

3

"Evaluate" needs both sides + use of data. Identify winners and losers; quote from the data given; reach a judgement.

Next: Lesson 7.09

Biodiversity, Waste Management, Land Use, Deforestation & Maintaining Biodiversity (4.7.3.1–7.3.4, 7.3.6) — the human-impact angle in detail, with named conservation measures.