Topic 20.2 · Core
Biodiversity and Habitat Destruction
Biodiversity gets misread as a rough synonym for 'lots of animals' more often than any other term in this chapter. For this syllabus it means something narrower and more precise, and getting that definition exactly right is worth more than it looks.
What biodiversity actually measures
For this Cambridge syllabus point, biodiversity is the number of different species living in an area. An area holding an enormous population of just one or two species has low biodiversity, even though the total number of organisms is huge; an area with fewer organisms overall but many different species present has higher biodiversity. The count that matters is species, not individuals.
Why humans destroy habitats
Cambridge specifies six reasons behind habitat destruction, and a strong answer names the specific one a question is pointing at rather than reaching for a general “humans damage the environment” statement: expanding the area used for housing, for crop production, and for livestock production; extracting natural resources such as timber or minerals; and pollution of freshwater or marineenvironments. That last pair is worth pausing on, because it shows a habitat doesn’t have to be physically cleared to be destroyed — changing the water quality of an existing habitat can make it unsuitable for the species that depended on it, with the physical space left completely intact.
What happens once habitat is lost
Organisms depend on a habitat for food, shelter, breeding sites and the physical conditions they need to survive. Take any of those away and population sizes can fall; organisms may move elsewhere if suitable habitat still exists, but where it doesn’t, local extinction becomes possible, and in severe or widespread cases the species can be lost entirely. It’s worth keeping the two ideas separate rather than treating them as interchangeable: habitat destruction is the loss or degradation of the place and conditions organisms need, while biodiversity loss is the resulting reduction in the number of species present. One causes the other, but they are not the same statement said twice.
Habitat destruction through food webs
Habitat destruction doesn’t always work by bulldozing a species’ home directly — it can also work by changing the feeding relationships that species depends on. Removing or sharply reducing one species shifts the food available to its predators and the pressure it was placing on its prey or competitors, so a population that was never directly targeted can still rise or fall as a knock-on effect. This is exactly the food-web reasoning built up in Chapter 19: biodiversity is really what those food webs depend on for stability, since fewer species usually means fewer feeding routes and less resilience if any one part of the web changes.
Deforestation as a case study
Every mechanism above shows up at once, and at a larger scale, in a single specific form of habitat destruction that Cambridge treats as its own topic: deforestation, where clearing forest doesn’t just remove habitat but also destabilises soil, alters water movement and shifts the carbon cycle at the same time.