What is predation? Explain the roles of predators in an ecosystem and describe how prey defend themselves.
How to lay out the answer. Follow the frame, then write it in your own words.
1 · Define in one line. Predation is a (+, −) interaction in which a predator feeds on its prey; herbivores are predators of plants.
2 · Role 1: energy transfer. Predators pass the energy fixed by plants to higher trophic levels.
3 · Role 2: control of prey. They keep prey numbers in check; the prickly pear cactus in Australia was controlled by a cactus-feeding moth. Biological control works this way.
4 · Role 3: species diversity. They reduce competition among prey; removing the starfish Pisaster led to the extinction of over 10 invertebrate species.
5 · Describe prey defences.
Camouflage in some insects and frogs.
The distasteful Monarch butterfly.
Thorns in Acacia and cactus.
Poisonous cardiac glycosides in Calotropis.
6 · Link to real life. Farmers use ladybird beetles to control aphids, and the caffeine in tea is a plant defence chemical.
7 · Close in one line. So predation keeps ecosystems balanced and drives the evolution of prey defences.
Scoring tip: Name the textbook examples: Pisaster, the prickly pear and its moth, the Monarch butterfly and Calotropis. Examples carry the marks.
