Habitat DestructionCambridge IGCSE Biology: Revision notes
Section 1
What is biodiversity?
Biodiversity is the number of different species that live in an area. High biodiversity generally makes an ecosystem more stable and resilient; habitat destruction is one of the biggest threats to biodiversity worldwide.
Section 2
Why do humans destroy habitats?
Humans destroy natural habitats for several reasons:
- increased area for housing — expanding towns and cities replace natural habitats
- crop plant production — clearing land to grow food crops
- livestock production — clearing land for grazing animals
- extraction of natural resources — for example mining, quarrying and logging
- freshwater and marine pollution — contaminates and destroys aquatic habitats even without physically removing them
Section 3
How habitat destruction disrupts food webs
Habitat destruction alters the food webs and food chains within an ecosystem. Removing a habitat removes the species that lived there, which breaks the feeding links connecting them to other species. This can cause knock-on population changes throughout the whole food web — even for species not directly affected by the habitat loss itself.
When explaining habitat destruction in an exam, always mention that it disrupts food webs, not just the species living directly in that habitat.
Section 4
Deforestation: a case study in habitat destruction
Deforestation is a major and well-studied form of habitat destruction, with several undesirable effects:
- reducing biodiversity — many species lose their habitat entirely
- extinction — species with nowhere else to live may die out completely
- loss of soil — without tree roots to bind it, soil is eroded by wind and rain
- flooding — fewer trees means less water is intercepted and absorbed, increasing surface run-off
- increase of carbon dioxide in the atmosphere — fewer trees remove less CO2 by photosynthesis, and burning cleared vegetation releases stored carbon directly
Clearing rainforest for cattle grazing removes habitat, increases soil erosion on the exposed land, and releases carbon dioxide both from burning vegetation and from the loss of photosynthesising trees.
Section 5
When habitat loss leads to extinction
Habitat destruction is one of the main reasons organisms become endangered or extinct (along with climate change, hunting, overharvesting, pollution and introduced species). As habitat area shrinks, population size falls, which reduces genetic variation and makes the remaining population less able to survive further environmental change or disease — increasing the risk of complete extinction.
Endangered species can be conserved through monitoring and protecting species and habitats, education, captive breeding programmes, and seed banks.
Don't say habitat destruction only affects the species living there directly — it also reduces genetic variation in surviving populations, making them vulnerable long-term.
Must Know
- Biodiversity is the number of different species living in an area.
- Humans destroy habitats through housing, crop and livestock production, resource extraction, and pollution.
- Habitat destruction disrupts food webs, causing knock-on effects across a community.
- Deforestation reduces biodiversity, causes extinction, soil loss, flooding, and increases atmospheric CO2.
- Shrinking habitats reduce population size and genetic variation, increasing extinction risk.
- Endangered species are conserved through monitoring/protection, education, captive breeding and seed banks.
That's the notes covered.
Carry on to the next subtopic.