AP® Environmental Science review sheet from Aim for Five (aimforfive.com/enviro/units/9/9-10)
Unit 9 · Topic 9.10
9.10 Human Impacts on Biodiversity
Human activity is driving species loss far faster than the natural background rate. Habitat loss and fragmentation are the biggest threats, and the main causes are summed up as HIPPCO. Protected areas, wildlife corridors, habitat restoration and sustainable land use are the main ways to protect biodiversity.
Key terms
- habitat loss
- habitat fragmentation
- HIPPCO
- wildlife corridor
- overexploitation
- protected area
HIPPCO: the main threats
| Letter | Threat | Example |
|---|---|---|
| H | Habitat destruction and fragmentation | Clearing tropical forest for cattle ranches and soybean or palm oil plantations |
| I | Invasive species | Burmese pythons eating native mammals in the Everglades (topic 9.8) |
| P | Population growth | More people need more land, water, food and energy |
| P | Pollution | Pesticides, fertilizer runoff, plastics, oil spills |
| C | Climate change | Species forced to shift ranges; coral bleaching |
| O | Overexploitation | Overfishing, poaching, overhunting, such as the passenger pigeon, hunted to extinction by 1914 |
Habitat loss and fragmentation
Habitat loss is the single largest threat to biodiversity. Habitat fragmentation is when roads, farms, logging and development break a large habitat into smaller, isolated patches. It harms species even when total habitat area doesn't shrink much:
Small patches support small populations, which are more likely to die out from bad luck, disease or a bad year, and lose genetic diversity through inbreeding. Roads and fields block animals from moving to find mates, food or new territory, and animals that try to cross are often killed. Edge effects change conditions at the borders of each patch, making them hotter, drier, windier and more exposed to predators and invasive species, so interior species lose habitat as edges multiply.
These ideas connect to island biogeography (topic 2.3): habitat patches act like islands, and smaller, more isolated 'islands' hold fewer species.
Other human impacts
Climate change shifts the conditions species need, sometimes faster than they can move or adapt. Domestication has kept some species abundant (there are far more cattle and chickens today than their wild ancestors ever numbered), but relying on a few high-yield crop varieties and breeds has reduced genetic diversity in agriculture, leaving crops more vulnerable to new diseases and pests. Overexploitation can be dramatic: American bison fell from tens of millions to fewer than a thousand by the late 1880s.
Ways to protect biodiversity
- Protected areas such as national parks, wildlife refuges and marine protected areas. In 2022, nearly 200 countries agreed to a global goal of protecting 30 percent of land and ocean by 2030.
- Wildlife corridors: strips of habitat, such as forested river corridors, or structures like highway overpasses and underpasses that connect isolated patches. Banff National Park in Canada uses overpasses over a major highway, and wildlife crossings have sharply cut collisions there.
- Habitat restoration: replanting native vegetation, removing invasive species, restoring wetlands and streams.
- Sustainable land use: sustainable forestry and agriculture that keep habitat functioning while producing food and wood (topics 5.15 and 5.17).
- Laws and treaties that limit overexploitation and protect endangered species (topic 9.9), plus reducing pollution and greenhouse gas emissions.
Worked examples
Try each one yourself first, then open the solution.
- Example 1Calculator allowed
How fragmentation shrinks interior habitat
A square forest measures 10 km by 10 km. Edge effects extend 1 km into the forest from every edge, so only land more than 1 km from an edge is good interior habitat. (a) How much interior habitat does the forest have? (b) A road (assume its width is negligible) is built straight through the middle, splitting the forest into two 5 km × 10 km halves. How much interior habitat is left? (c) What percent of interior habitat was lost?
Show the solutionHide the solution
- Step 1: (a) Removing 1 km from each side leaves an interior square of (10 − 2) km × (10 − 2) km = 8 km × 8 km = 64 km².
- Step 2: (b) Each half is 5 km × 10 km. Removing 1 km from every edge, including the new road edge, leaves (5 − 2) km × (10 − 2) km = 3 km × 8 km = 24 km². Two halves: 2 × 24 = 48 km².
- Step 3: (c) Percent lost = (64 − 48) ÷ 64 × 100 = 16 ÷ 64 × 100 = 25%.
- Step 4: Notice the forest's total area is still about 100 km², yet interior species lost a quarter of their habitat.
Answer: (a) 64 km². (b) 48 km². (c) 25% of interior habitat lost, with almost no change in total forest area.
- Example 2
Proposing and justifying a solution
A new highway separates a mountain lion population's hunting grounds from its denning areas. Propose one solution and explain how it helps the population.
Show the solutionHide the solution
- Step 1: Problem: the highway fragments the habitat, blocks movement and causes roadkill when animals try to cross.
- Step 2: Solution: build a wildlife crossing (an overpass covered with native vegetation, or an underpass), with fencing that guides animals toward it.
- Step 3: Benefit: lions can reach both hunting and denning areas safely, collisions drop, and individuals from both sides can mate, keeping genetic diversity higher.
Answer: Build a vegetated wildlife overpass or underpass with guide fencing; it reconnects the habitat, reduces roadkill and keeps the population genetically connected.
Common mistakes
- Saying fragmentation is harmless if total area stays the same. Smaller, isolated patches with more edge support fewer species and smaller populations.
- Listing 'pollution' or 'climate change' as the leading threat. Habitat loss is generally the biggest single cause of biodiversity decline.
- Describing a wildlife corridor as a protected area. A corridor connects habitats; its main job is allowing movement.
On the exam
- Expect to identify a human cause of biodiversity loss in a scenario and propose a specific solution, such as a wildlife corridor for fragmentation.
- Edge-effect and habitat-area calculations can appear; draw the shape and subtract the edge from each side.
Connected topics
Videos
Check yourself
4 questions on 9.10 Human Impacts on Biodiversity. Pick an answer to see if you got it, and why.
| Forest fragment | Area (hectares) | Forest-interior bird species |
|---|---|---|
| 1 | 1 | 2 |
| 2 | 10 | 7 |
| 3 | 100 | 15 |
| 4 | 1,000 | 24 |
Hypothetical survey data from fragments of a once-continuous forest
Which conclusion is best supported by the data?
Which action would best help forest-interior birds in the smaller fragments?
A tropical frog species is declining because its forest is cleared for palm oil plantations, a non-native fungus is infecting it, and collectors capture it for the pet trade. Which parts of HIPPCO are affecting the frog?
Commercial honeybee colonies are bred for traits such as high honey production and gentleness. Which is a likely consequence of this domestication?
0 of 4 answered