Ecosystems and Biomes: KS3 Geography Explained

An ecosystem is a community of living organisms — plants, animals, and microorganisms — interacting with each other and with their non-living environment (soil, water, climate, and nutrients). Every component depends on every other: remove one and the whole system shifts. A biome is a large-scale ecosystem sharing a broadly similar climate and vegetation type.

What is an ecosystem and what does it contain?

The word "ecosystem" was coined by British ecologist Arthur Tansley in 1935. It describes not just the organisms living in a place but the full set of relationships between those organisms and their physical environment.

Every ecosystem has two fundamental components:

Biotic (living) components:

Producers (autotrophs): Plants and algae that convert sunlight into energy through photosynthesis. They form the base of every food web.

Primary consumers: Herbivores that eat plants (rabbits, caterpillars, deer).

Secondary consumers: Carnivores or omnivores that eat herbivores (foxes, sparrowhawks, weasels).

Tertiary consumers: Predators at the top of the food chain (golden eagles, large predatory fish).

Decomposers: Bacteria and fungi that break down dead organic matter, returning nutrients to the soil and completing the cycle.

Abiotic (non-living) components:

Climate (temperature, rainfall, seasonality)

Soil type (composition, drainage, pH, nutrient content)

Topography (altitude, slope, aspect)

Water availability

Light intensity

The interaction between biotic and abiotic components makes every ecosystem unique — and explains why changing one element (such as temperature, through climate change) triggers cascading effects across all others.

How do food webs show energy transfer?

A food chain is a simple, linear sequence showing what eats what:

Grass → Rabbit → Fox → Golden eagle

A food web is more realistic: it shows the multiple, overlapping pathways through which energy passes in an ecosystem. In a UK deciduous woodland, for example:

Oak trees, hawthorn, bramble → caterpillars → blue tits → sparrowhawks

Oak trees → grey squirrels → tawny owls

Leaf litter → earthworms → blackbirds → foxes

All dead matter → decomposers (earthworms, fungi, bacteria) → soil nutrients → plants

Energy transfer is inefficient. Only approximately 10 per cent of the energy at one trophic level (feeding level) passes to the next. The rest is lost as heat during respiration, used for movement, or passed to decomposers. This explains why food chains rarely exceed five links, and why ecosystems can support far more herbivores than carnivores, and far more plants than herbivores.

Trophic level | Example (UK woodland) | Approx. energy available
Producer (plants) | Oak, hawthorn, grass | 100%
Primary consumer (herbivore) | Rabbit, caterpillar | ~10%
Secondary consumer (carnivore) | Fox, sparrowhawk | ~1%
Tertiary consumer (top predator) | Golden eagle | ~0.1%

This pyramid of energy has direct consequences for conservation: removing a top predator (such as wolves from British uplands, extirpated centuries ago) does not just remove one species — it alters the behaviour and population dynamics of everything below it.

What is a biome and how are they distributed globally?

A biome is a large-scale ecosystem characterised by a distinct climate, vegetation type, and associated animal life. Biomes are distributed globally according to latitude (distance from the equator) and altitude (height above sea level), both of which affect temperature and rainfall.

The major terrestrial biomes include:

Biome | Climate | Location examples
Tropical rainforest | Hot, wet all year (>2,000 mm rain/yr) | Amazon Basin, Congo Basin, SE Asia
Tropical grassland (savanna) | Hot, distinct wet and dry seasons | Sub-Saharan Africa, northern Australia
Hot desert | Hot days, cold nights; very low rainfall (<250 mm/yr) | Sahara, Arabian Desert, Atacama
Mediterranean scrub | Hot dry summers, mild wet winters | Southern Europe, California
Temperate deciduous forest | Moderate temperature, 4 seasons; 600–1,500 mm rain/yr | Western Europe, eastern North America
Boreal forest (taiga) | Long cold winters, short warm summers | Canada, Russia, Scandinavia
Tundra | Extremely cold; permafrost; very low precipitation | Arctic regions, high mountain tops

Global biome distribution broadly mirrors climate zones: tropical biomes near the equator, where solar radiation is most intense; cold biomes at higher latitudes; desert biomes at approximately 30° North and South, where descending air in the Hadley Cell creates dry conditions.

Altitude creates a vertical zonation that mirrors latitudinal change: climbing a high mountain in the tropics, you pass from tropical rainforest at the base, through temperate forest, then alpine meadow, and finally to a zone resembling arctic tundra at the summit.

What does a UK deciduous woodland ecosystem look like?

The UK's native biome — temperate deciduous woodland — is one of the most studied ecosystems in the world and a useful local example for KS3.

Climate: Moderate year-round temperatures, typically 8–12°C annual average in lowland England; 600–800 mm of rain spread across the year.

Vegetation structure: Deciduous woodland has a layered structure:

Canopy layer: Dominant trees (oak, ash, beech, elm) at 15–30 m, which intercept most light in summer.

Shrub layer: Hazel, hawthorn, holly, and elder at 5–15 m.

Field layer: Bluebells, brambles, bracken, and ground-covering flowering plants — many bloom in spring before the canopy closes and shades them out.

Ground layer: Mosses, lichens, and leaf litter.

Characteristic food web: A simplified UK deciduous woodland food web:

Producers: oak, hawthorn, hazel, bramble, bluebell

Primary consumers: caterpillars, aphids, rabbits, grey squirrels, woodmice, deer

Secondary consumers: blue tits, robins, hedgehogs, weasels

Tertiary consumers: tawny owl, sparrowhawk, fox

Decomposers — including earthworms, woodlice, millipedes, and hundreds of fungal and bacterial species — are essential for breaking down the leaf litter that accumulates each autumn, releasing the nutrients that allow producers to grow the following spring.

In practice, very little ancient deciduous woodland remains in the UK: most was cleared for agriculture centuries ago. Ancient woodland (defined as woodland that has existed continuously since at least 1600) covers only about 2.5 per cent of the UK's land area.

What are the human threats to ecosystems?

Ecosystems across the world — including the UK's remnant woodlands — face a range of human-driven threats. The SEEP lens helps organise them:

Environmental: Climate change is altering temperature and rainfall patterns, shifting the ranges of species and disrupting the timing of seasonal events (such as the synchrony between caterpillar emergence and bird breeding). Deforestation for agriculture or logging destroys habitat and fragments ecosystems, reducing biodiversity and disrupting nutrient cycles.

Economic: Agricultural intensification — use of pesticides, fertilisers, and monocultures — reduces the diversity of habitats and directly kills insects and other invertebrates. The UK has lost 97 per cent of its wildflower meadows since the 1930s, largely through agricultural improvement.

Social: Invasive non-native species (introduced deliberately or accidentally through trade and travel) can displace native species. The American grey squirrel, introduced to Britain in the 1870s, has almost eliminated the native red squirrel from England and Wales by outcompeting it and carrying the squirrelpox virus (to which red squirrels have no immunity).

Political: Ecosystem protection depends on national and international policy (e.g. protected areas, environmental legislation, international biodiversity agreements). Weak enforcement or policy reversals can rapidly undermine decades of conservation effort.

The concept of interdependence — that every species in an ecosystem depends, directly or indirectly, on every other — means that human threats do not affect species in isolation. Removing pollinators (bees and other insects) affects the plants that depend on them for reproduction; changing plant communities affects the herbivores; altered herbivore populations affect predators. These cascading effects make ecosystem management a genuinely complex, system-level challenge.

Frequently asked questions

What is the difference between an ecosystem and a biome?

An ecosystem is any community of living organisms interacting with their non-living environment — it can be as small as a pond or a woodland clearing. A biome is a much larger-scale classification: a broad type of ecosystem (such as tropical rainforest or tundra) defined by its climate and dominant vegetation type. A single biome contains many individual ecosystems, each with slightly different species assemblages.

Why is interdependence important in geography?

Interdependence means that every component of an ecosystem — every species, every nutrient cycle, every abiotic factor — is connected to every other. This matters geographically because changes in one part of a system (whether from climate change, land use, or an invasive species) ripple through the whole system in ways that are difficult to predict. Simple, single-cause explanations of environmental change are almost always incomplete.

How does latitude affect biome distribution?

Solar radiation is most intense at the equator and decreases towards the poles, creating a temperature gradient from tropical to polar regions. Since temperature is a primary control on vegetation type, biome distribution broadly mirrors latitude: tropical rainforests near the equator; temperate forests at mid-latitudes (roughly 40–60°); boreal forests and tundra at high latitudes. Rainfall patterns — controlled by atmospheric circulation — further modify this basic pattern.

What can be done to protect ecosystems in the UK?

Conservation approaches include expanding protected areas (Sites of Special Scientific Interest and National Parks), rewilding (reintroducing lost species, reducing active management), habitat restoration (replanting native woodland, restoring peat bogs and wildflower meadows), and agri-environment schemes that pay farmers to manage land in wildlife-friendly ways. At the local level, school wildlife gardens and urban green corridors help maintain biodiversity in fragmented landscapes.

For Socratic KS3 geography practice that builds your understanding of living systems and global patterns, visit aitutors.me.