Read Why Predators Protect Diversity
Predators do more than eat prey. In these questions, identify what a predator controls, what happens when it is removed, and how prey avoid being eaten.
Predation and Diversity is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Read a predator-removal experiment
In the NSEB Pisaster graph, species richness stays high before sea-star removal but falls sharply after removal. Pisaster preys on mussels; without it, mussels can monopolise space and competitively exclude other species. The graph supports a keystone-predator role. Do not call the mussel the keystone predator or infer that the sea star directly competed with every species.
Predict the indirect effect
A predator normally limits prey abundance. Remove the predator and prey can become numerous, deplete shared resources, and intensify competition. Predators can therefore help maintain diversity and stability, even though each individual predation event harms prey. This is top-down control of a community.
Recognise defence and control examples
Prey may avoid predators by camouflage or deter them through distasteful chemicals and physical structures such as thorns. Plants defend against herbivores with compounds including nicotine and caffeine. Herbivory is often named separately, but in a broad ecological sense the herbivore is a predator of plants. Introduced species may spread when their natural predators are absent.
Interpret 'prudent' without intent
Textbooks call predators 'prudent' because unchecked exploitation can eliminate prey, then leave predators without food. This does not mean predators consciously calculate conservation. In assertion–reason items, connect overexploitation to the risk of losing both populations.
OlympIQ exam lens
- ✓Predator removal → release of dominant prey → stronger competition → possible loss of other species.
- ✓Pisaster is the predator; mussels are the prey that can dominate space.
- ✓Camouflage, distastefulness, thorns and defensive chemicals can protect prey.
- ✓Herbivores count as predators in the broad ecological sense.
- ✓Overexploitation can harm predator and prey; 'prudent' does not imply intent.
When a graph shows fewer species after predator removal, the missing predator may have protected diversity indirectly by suppressing a strong competitor. Separate that mechanism from direct competition by the predator itself.
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