# Human Impacts and Future Ecosystems

> How people change ecosystems through habitat loss, invasive species, pollution and climate change, and how we can restore them, including Aboriginal fire management.

From HSC Biology on WhizzNotes, free study notes for NSW students: https://whizznotes.com/biology/future-ecosystems/. Updated 3 November 2026.
Year 11 and Year 12 boxes go deeper than the Year 10 text around them.

### Story time: The fox-free island
Dirk Hartog Island off Western Australia once had at least ten kinds of small native mammals. Sheep, goats and feral cats arrived, and most of them disappeared.

From 2014, workers removed every sheep, goat and cat from the island. Then they began bringing animals back: banded hare-wallabies, rufous hare-wallabies, dibblers, woylies and more. Many are breeding well. The island is slowly returning to something like the ecosystem it was 200 years ago. Damage can be fast, but with planning, some of it can be undone.

**In short:** Human activities such as habitat loss, invasive species, pollution, overharvesting and climate change are changing ecosystems and driving extinctions. Australia has lost more mammal species than any other continent, and solutions include protected areas, feral animal control, revegetation and cultural burning.

## Starting point: what you already know

- Food webs link species, so a change to one can affect many (see Ecosystems, Food Webs and Energy Flow).
- Populations are limited by food, space, predators and disease (see Population Dynamics and Sampling).
- Burning fossil fuels adds $\mathrm{CO_2}$ to the air.

## How humans change ecosystems

| Impact | What happens | Australian example |
|---|---|---|
| **Habitat loss** | Land cleared for farms, cities and roads | Almost 40% of Australia's forests have been cleared since 1788 |
| **Fragmentation** | Habitat broken into small patches | Koalas cross roads between patches and get hit by cars |
| **Invasive species** | Introduced species spread and harm natives | Foxes and cats eat small mammals. Rabbits strip vegetation. Cane toads poison predators |
| **Pollution** | Chemicals, plastics and nutrients enter ecosystems | Fertiliser run-off causes algal blooms in rivers. Plastic harms turtles and seabirds |
| **Climate change** | Warmer, more extreme weather | Mass coral bleaching on the Great Barrier Reef. Bigger, hotter bushfires |
| **Overharvesting** | Taking species faster than they breed | Overfishing of some fish stocks |

Australia has the worst rate of mammal extinction of any continent, with more than 30 mammal species lost since 1788. Feral cats and foxes are a major cause.

### Worked example: Eutrophication step by step
1. Fertiliser washes into a river after rain.
2. Extra nitrates and phosphates make algae grow fast (an **algal bloom**).
3. Algae block light and plants below die.
4. Decomposers break down the dead plants and algae and use up the oxygen.
5. Fish suffocate. Large fish kills in the Darling River have followed this kind of chain.

## Looking after future ecosystems

- **Protected areas**: national parks and marine parks.
- **Wildlife corridors**: strips of habitat that link patches so animals can move and breed.
- **Feral animal control**: fencing, baiting and predator-free islands and sanctuaries.
- **Revegetation**: replanting local native species.
- **Captive breeding** and reintroduction, as in the story.
- **Reducing emissions** to slow climate change.

## Cultural burning

For tens of thousands of years, Aboriginal people have cared for Country with **cultural burning**: small, cool, patchy fires lit at the right time and place, following knowledge of plants, animals and seasons.

- Cool fires burn slowly and low, so trees and animals survive.
- They reduce fuel, so later wildfires are less intense.
- The mosaic of burnt and unburnt patches gives animals food and shelter.

After the 2019 to 2020 bushfires, more fire agencies began working with Aboriginal fire practitioners. This knowledge belongs to the communities who hold it, and it is shared on their terms.

**Mind map**

```text
Human impacts
  Damage
    Habitat loss and fragmentation
    Invasive species
    Pollution and eutrophication
    Climate change
    Overharvesting
  Solutions
    Protected areas
    Wildlife corridors
    Feral control
    Revegetation
    Captive breeding
  Cultural burning
    Cool, patchy fires
    Less fuel
    Knowledge shared on community terms
```

### Year 11: Predicting future ecosystems
Scientists use **models** to predict how ecosystems will change, based on past data and present trends. For example, as temperatures rise, many species are moving their ranges **south** or **uphill**. Species that cannot move fast enough, like the mountain pygmy possum in the Australian Alps, face high risk.

Evaluating a solution in an exam: say **what** it is, **how** it helps, and give a **limitation**. Example: "Wildlife corridors let koalas move between patches, increasing gene flow, but they are costly and need land that farmers may use."

**Biological control** uses a natural enemy to control a pest. The myxoma virus and calicivirus reduced rabbits. The cane toad, released to control beetles, is a famous failure, which is why biological controls are now tested carefully before release.

### Year 12: Biodiversity and genetic diversity
Small, isolated populations lose **genetic diversity** through inbreeding and genetic drift (Module 6). This makes them less able to adapt to change or disease. Tasmanian devils have very low genetic diversity, which is one reason devil facial tumour disease (a contagious cancer) spread so easily. Conservation programs now track genetic diversity as well as numbers.

## Quick summary

- Habitat loss, fragmentation, invasive species, pollution, climate change and overharvesting all damage ecosystems.
- Australia has lost more mammal species than any other continent, largely to cats and foxes.
- Fertiliser run-off causes algal blooms and fish kills (eutrophication).
- Solutions include protected areas, corridors, feral control, revegetation and captive breeding.
- Aboriginal cultural burning uses cool, patchy fires to reduce fuel and care for Country.

## Quiz

Try these questions from the chapter quiz.

1. Which is an invasive species in Australia?
   - A. Koala
   - B. Wombat
   - C. European red fox
   - D. Kookaburra
   - Answer: C. European red fox. Foxes were introduced and prey on native animals.

2. Breaking a forest into small separate patches is called
   - A. fragmentation
   - B. revegetation
   - C. eutrophication
   - D. speciation
   - Answer: A. fragmentation. Habitat is split into fragments.

3. What causes an algal bloom in a river?
   - A. Too little light
   - B. Extra nutrients such as fertiliser run-off
   - C. Cold weather
   - D. Too many fish
   - Answer: B. Extra nutrients such as fertiliser run-off. Nitrates and phosphates feed fast algal growth.

The whole chapter quiz is on the page, for signed-in students: https://whizznotes.com/biology/future-ecosystems/#quiz