Study Notes: Habitat Destruction (IGCSE Biology 0610)

Hello future Biologists! Welcome to this crucial chapter on Human Influences on Ecosystems. This topic helps us understand the significant impact our actions have on the planet's life support systems. We will focus specifically on how and why we destroy natural habitats and what the big consequences are.

Don't worry if conservation seems overwhelming—we’ll break down these big global problems into simple biological concepts. Let’s get started!


1. What is Biodiversity? (Core 20.2.1)

Before we talk about destroying habitats, we must understand what we are losing.

Defining Biodiversity

Biodiversity simply means the variety of life in an area. It is described as:

  • The number of different species that live in an area.

A rainforest has very high biodiversity (lots of different plants, animals, fungi, and microorganisms), while a field growing only one type of crop (a monoculture) has very low biodiversity.

Why is high biodiversity important?

Imagine a football team. If the team only has strikers, they might score goals, but they will fall apart defensively. A team with a variety of players (defenders, midfielders, keepers) is much stronger and more stable. In the same way:

  • Ecosystems with high biodiversity are more stable and resilient (can recover easily) from changes like disease or minor climate shifts.
  • Each species plays a vital role (e.g., pollination, decomposition). Removing one species can cause the whole ecosystem to collapse.
Quick Review: Biodiversity

Biodiversity = Variety of different species in an area.
High biodiversity = Stable ecosystem.


2. Reasons for Habitat Destruction (Core 20.2.2)

Habitat destruction occurs when humans remove or severely damage the natural environment where organisms live. This is usually driven by our increasing need for resources and space.

Major Causes of Habitat Destruction

Habitat destruction can be categorised into three main areas:

1. Increased Land Use (Housing and Agriculture)

As the human population grows, we need more space to live and more food to eat. This leads to:

  • Housing: Clearing natural land (like forests or wetlands) to build towns, cities, and infrastructure (roads).
  • Crop Plant Production (Farming): Natural grasslands or forests are converted into fields for agriculture.
  • Livestock Production: Huge areas of land are needed for grazing animals (like cattle) or for growing their feed.

Example: In the Amazon, vast areas of rainforest are cleared (deforested) to create space for cattle ranching or soya bean farms.

2. Extraction of Natural Resources

We need raw materials for industry and technology, which often involves damaging habitats to get them:

  • Mining: Digging deep holes or strip-mining requires removing large amounts of surface rock and soil, destroying the habitat above.
  • Logging: Cutting down trees for timber (wood) removes the homes of countless forest organisms.
3. Pollution (Freshwater and Marine)

Pollution doesn't always physically remove a habitat, but it makes it toxic or unsuitable for organisms to survive, effectively destroying the habitat's function.

  • Freshwater Pollution: Runoff from farms (fertilisers and pesticides) or waste from industry can kill aquatic life in rivers and lakes.
  • Marine Pollution: Large amounts of plastic waste, oil spills, and chemical runoff devastate ocean habitats, especially coral reefs and deep-sea environments.

Did you know? Even noise pollution can damage habitats. Constant loud noise can prevent animals from communicating, mating, or hunting successfully.


3. Undesirable Effects of Habitat Destruction

A. Impact on Food Webs (Core 20.2.3)

Ecosystems rely on complex food webs where energy is transferred from producers to consumers. When a habitat is destroyed, these webs fall apart.

  • If you remove a single species of plant (the producer), all the herbivores that eat it suffer.
  • If the herbivores die, the carnivores that rely on them starve.
  • This results in a domino effect, meaning a negative impact on one part of the web leads to the collapse of many other parts.

When humans alter food chains (e.g., by overharvesting a specific fish species), we remove a key link, leading to negative effects across the entire habitat.

B. The Specific Example of Deforestation (Core 20.2.4)

Deforestation is the large-scale removal of forests. The syllabus requires you to know several undesirable effects of this specific type of habitat destruction.

Effects of Deforestation:
  1. Reducing Biodiversity:

    Removing the trees immediately removes the habitat for countless species (insects, birds, mammals) that live in or rely on those trees. This drastically reduces the number of different species in the area.

  2. Extinction:

    If a species lives only in that specific forest habitat (it is endemic), and the forest is cleared, the species will likely go extinct (die out completely). Extinction is irreversible.

  3. Loss of Soil (Erosion):

    Tree roots act like glue, holding the soil together. When trees are cut down, the soil is exposed to heavy rain and wind. The topsoil (which is rich in nutrients) is quickly washed or blown away. This process is called soil erosion.

  4. Flooding:

    Trees play a critical role in the water cycle. Their leaves intercept rainfall, and their roots absorb massive amounts of water from the soil. Without trees, rainfall hits the ground hard, cannot be absorbed quickly, and runs directly into rivers, increasing the risk of flooding downstream.

  5. Increase of Carbon Dioxide in the Atmosphere:

    Forests are sometimes called "carbon sinks" because they take in huge amounts of CO₂ for photosynthesis. Deforestation increases atmospheric CO₂ in two ways:

    • Less Photosynthesis: Fewer trees mean less CO₂ is removed from the air.
    • Burning/Decomposition: If the cleared wood is burned, or if it is left to rot (decompose), the stored carbon is released directly back into the atmosphere as CO₂.

    This increase in CO₂ contributes to the enhanced greenhouse effect and climate change.

Memory Aid for Deforestation Effects (The FICES Mnemonic)

To remember the five key undesirable effects of deforestation easily, remember the acronym FICES:

Flooding
Increased CO₂
Carbon Dioxide Increase
Extinction / Erosion (Soil Loss)
Species Loss (Reducing Biodiversity)


Key Takeaways on Habitat Destruction

  • Biodiversity is the variety of species, making ecosystems stable.
  • Habitat destruction is driven mainly by the need for more land (housing, farming) and resources (mining).
  • Deforestation causes soil erosion (no roots to hold soil), increased flooding (no interception/absorption), and contributes to climate change by releasing CO₂.
  • Destroying one habitat has ripple effects across the whole food web.

Keep these points clear, and you will be able to ace any exam question on the human influence on habitats!