Predation in Ecosystems

Term 1, Week 2, Lesson 3

Do Now

Examine the images of the three Australian animals below. For each one, predict whether it is a predator, prey, or both. Write one sentence justifying your reasoning for each.

1. Wedge-tailed eagle
2. Quokka
3. Eastern brown snake

Wedge-tailed eagle, quokka, eastern brown snake.

Daily Review

1. Competition between members of the same species is called:
   • 1. Interspecific competition
   • 2. Intraspecific competition
   • 3. Predation
   • 4. Symbiosis
2. Which of the following is an example of interspecific competition?
   • 1. Two male kangaroos fighting over a mate
   • 2. Feral cats and quolls hunting the same prey
   • 3. A pack of wolves hunting together
   • 4. Bacteria decomposing leaf litter
3. The competitive exclusion principle states that:
   • 1. Two species can always share the same niche
   • 2. Competition only occurs between different species
   • 3. Two species competing for the same niche cannot coexist indefinitely
   • 4. All organisms must compete for mates
4. An abiotic factor in a desert ecosystem would include:
   • 1. Lizards
   • 2. Cacti
   • 3. Bacteria
   • 4. Temperature
5. Resource partitioning allows species to coexist by:
   • 1. Eliminating competition entirely
   • 2. Using the same resources at the same time
   • 3. Dividing up resources to reduce direct competition
   • 4. Increasing the number of predators in the ecosystem

Learning Intentions

Today we are learning about predator-prey relationships and how predation influences population dynamics in ecosystems.

Success Criteria

• Define predation and identify the roles of predator and prey in an ecosystem
• Describe adaptations that predators and prey have developed in response to each other
• Interpret predator-prey population graphs to explain cyclical changes in population size

Keywords

predation

An interaction where one organism (the predator) hunts and consumes another organism (the prey).

predator

An organism that hunts and eats other organisms.

prey

An organism that is hunted and eaten by a predator.

adaptation

A feature or behaviour that helps an organism survive in its environment.

camouflage

Colouring or patterns that help an organism blend in with its surroundings.

mimicry

When one species evolves to resemble another species (often a dangerous one) to avoid predation.

predator-prey cycle

The cyclical rise and fall of predator and prey populations over time.

Learning Activities

Activity 1 — I DO: Predator-Prey Relationships and Adaptations

Teacher presents predator and prey adaptations using Australian examples, then introduces predator-prey population graphs.

Key points to cover:

Predator Adaptations:

• Speed and agility: Wedge-tailed eagles can dive at over 300 km/h to catch prey.
• Stealth and ambush: Saltwater crocodiles lie motionless in water before striking.
• Venom: Eastern brown snakes use potent venom to immobilise prey quickly.
• Sharp claws and teeth: Quolls have sharp teeth adapted for catching and eating small mammals and insects.
• Camouflage: Wobbegong sharks blend into the reef floor to ambush fish.

Prey Adaptations:

• Camouflage: Leaf-tailed geckos blend in with tree bark to avoid detection.
• Warning colouration (aposematism): Blue-ringed octopus displays bright blue rings to warn predators of its deadly venom.
• Mimicry: Some harmless flies mimic the appearance of wasps to deter predators.
• Speed and escape: Wallabies use powerful hind legs to flee from predators at high speed.
• Defensive structures: Thorny devil lizards have spines covering their body to deter predators.

Predator-Prey Population Cycles:

• As prey populations increase → more food available → predator populations increase.
• As predator populations increase → more prey consumed → prey populations decrease.
• As prey populations decrease → less food → predator populations decrease.
• As predator populations decrease → less predation → prey populations recover.
• This creates a cyclical pattern with a time lag between predator and prey peaks.

Introduce the classic lynx and snowshoe hare dataset as an example of this cycle.

Check for Understanding: Mini-whiteboard: “If prey populations suddenly crash, what happens to predator numbers? Why is there a time lag?”

Predator-prey population cycle graph showing lynx and snowshoe hare.

Activity 2 — WE DO: Guided Graph Analysis

Students work through a predator-prey population graph step-by-step with the teacher.

Using the lynx-hare graph displayed on the board, work through the following as a class:

1. Identify which line represents the predator and which represents the prey.
2. Mark the peak of the prey population. What happens to the predator population shortly after?
3. Mark the peak of the predator population. What happens to the prey population shortly after?
4. Identify the time lag between the prey peak and the predator peak. Approximately how long is it?
5. Describe the overall pattern in one sentence.
6. Predict what would happen if a disease wiped out most of the hare population. Sketch the next part of the graph.

Activity 3 — YOU DO: Independent Graph Interpretation

Students independently interpret a new predator-prey graph and answer structured questions.

The graph below shows the estimated populations of dingoes and wallabies in a national park over a 20-year period.

Dingo and wallaby predator-prey population graph.

Answer the following questions:

1. Which organism is the predator and which is the prey? How can you tell from the graph?
2. In which year did the wallaby population reach its highest point?
3. What happened to the dingo population after the wallaby peak? Explain why.
4. Describe the relationship between the two population curves. What pattern do you notice?
5. Estimate the time lag between the wallaby population peak and the dingo population peak.
6. In Year 15, the wallaby population dropped sharply. Suggest two possible reasons for this — one related to predation and one related to an abiotic factor.
7. Predict what would happen to both populations if dingoes were removed from the national park. Explain your reasoning.

Reflection

1. Define predation in your own words.
2. Match the adaptation to the correct type:

Adaptation	Predator or Prey?
Camouflage to blend into the reef floor
Bright warning colours
Venomous bite to immobilise food
Spines covering the body

3. Explain why there is a time lag between changes in prey population and changes in predator population.
4. A predator-prey graph shows that the rabbit population is currently at a peak. Predict what will happen to the fox population over the next few years.