# Predator-Prey Interactions

Psychology I · Ethology · https://tryals.app/learn/psychology-i/predator-prey-interactions

## The Evolutionary Arms Race

Predator-prey interactions drive an endless **arms race**: prey adaptations favor counter-adaptations in predators, continuing the cycle indefinitely. 

**Crypsis** is camouflage helping an organism avoid detection. **Aposematism** is bright warning coloration used by toxic species so predators learn to avoid them.

| Strategy | Definition | Example |
| --- | --- | --- |
| **Crypsis** | Avoids detection | Camouflaged insect |
| **Aposematism** | Advertises toxicity | Poison dart frog |

According to the **Red Queen Hypothesis**, a species must keep evolving merely to maintain relative fitness, running just to stay in place.

## Mimicry & Group Defense

**Mimicry** exploits predator learning. In **Batesian mimicry**, a harmless species mimics a dangerous one, like a hoverfly resembling a wasp. In **Müllerian mimicry**, multiple dangerous species converge on a shared warning pattern.

| Mimicry Type | Core Mechanism | Free-Rider Status |
| --- | --- | --- |
| **Batesian** | Harmless mimics dangerous | Yes, free-rider |
| **Müllerian** | Both are dangerous | No, mutual benefit |

Group living offers protection via the **dilution effect** (individual risk falls as group size rises) and the **many-eyes effect** (increased collective vigilance).

## Practice questions

7 of this lesson's 12 practice questions, with answers. The full set is in the app.

### 1. Under the **Red Queen** hypothesis, a prey species that keeps evolving faster defences may end up no safer than it started. Why run at all?

A. Because predators stop evolving once prey defences become sufficiently strong
B. Because evolution has no direction, so the effort is genuinely wasted
C. Because the improvements accumulate and eventually the prey wins outright
D. Because the predator is improving too, so standing still loses

**Answer:** D. Because the predator is improving too, so standing still loses

**Why:** Both sides improve, so absolute gains cancel and only relative position matters. Stop adapting and you do not hold your ground, you lose it. This is why sexual reproduction is worth its enormous cost: shuffling defences faster than parasites can track them is the whole return.

Page: https://tryals.app/practice/psychology-i/predator-prey-interactions/under-the-red-queen-hypothesis-a-prey-species-that-keeps-evolving

### 2. Select every statement that is TRUE about predator-prey adaptations.

A. The many-eyes effect improves early detection of predators.
B. Aposematism advertises toxicity so predators learn to avoid the animal.
C. Joining a larger group cuts the chance that any given attack falls on you.
D. Batesian mimics are themselves toxic or dangerous.
E. Crypsis works by advertising an animal's toxicity.

**Answer:** A. The many-eyes effect improves early detection of predators.; B. Aposematism advertises toxicity so predators learn to avoid the animal.; C. Joining a larger group cuts the chance that any given attack falls on you.

**Why:** Aposematism, the dilution effect, and the many-eyes effect are all true. Crypsis conceals rather than advertises, and Batesian mimics are harmless (only their models are dangerous) - so those two are false.

Page: https://tryals.app/practice/psychology-i/predator-prey-interactions/select-every-statement-that-is-true-about-predator-prey-adaptations

### 3. A harmless hoverfly gains protection by resembling a stinging wasp. Yet if hoverflies become very common relative to wasps, the protection weakens. Why does the mimic's advantage depend on how rare it is?

A. Because the protection is borrowed from predators' experience.
B. Because mimicry only evolves in small populations and breaks down genetically once the population grows.
C. Because hoverflies compete with each other for food when abundant, which weakens them and makes them easier to catch.
D. Because predators can distinguish hoverflies from wasps individually, and simply encounter more hoverflies when they are common.

**Answer:** A. Because the protection is borrowed from predators' experience.

**Why:** Batesian mimicry is parasitic on a reputation the mimic did nothing to earn, and every hoverfly eaten without consequence is evidence against the rule. Contrast Müllerian mimicry, where each additional bearer is genuinely defended and strengthens the lesson, one system is undermined by its own success, the other reinforced by it.

Page: https://tryals.app/practice/psychology-i/predator-prey-interactions/a-harmless-hoverfly-gains-protection-by-resembling-a-stinging-wasp

### 4. Crypsis works by making an animal impossible to see. Aposematism works by making it impossible to miss. Both are anti-predator adaptations. How can advertising yourself to predators be a defence at all?

A. Because aposematism is only viable alongside a real defence.
B. Because bright colours startle a predator for long enough that the animal can escape.
C. Because conspicuous species are generally faster than cryptic ones, so being spotted costs them little.
D. Because predators prefer dull-coloured prey, so brightness works as a kind of camouflage in reverse.

**Answer:** A. Because aposematism is only viable alongside a real defence.

**Why:** A toxic caterpillar gains nothing from the predator that eats it; it gains from every other predator that ate one before and learned. Conspicuousness is what makes the lesson generalise, so the strategy trades individual concealment for population-level protection, and needs a real defence, a memorable signal and predators that learn, all at once.

Page: https://tryals.app/practice/psychology-i/predator-prey-interactions/crypsis-works-by-making-an-animal-impossible-to-see-aposematism

### 5. Sort each anti-predator strategy as crypsis or aposematism.

**Answer:**

- Crypsis (avoid detection): A moth colored exactly like tree bark, A stick insect resembling a twig, A flounder matching the seabed's pattern
- Aposematism (warning coloration): A bright poison-dart frog's vivid skin, A wasp's bold black-and-yellow stripes, A monarch butterfly advertising its toxicity

**Why:** Crypsis hides the animal (bark moth, twig insect, flounder); aposematism advertises toxicity with bold coloration (poison frog, wasp, monarch). One avoids detection; the other invites it, so predators learn to stay away.

Page: https://tryals.app/practice/psychology-i/predator-prey-interactions/sort-each-anti-predator-strategy-as-crypsis-or-aposematism

### 6. A harmless hoverfly mimicking a wasp is Batesian; several toxic butterflies converging on one pattern is Mullerian. Why does that difference change who benefits?

A. Because Mullerian mimicry requires the species to be closely related
B. Because Batesian mimics are always more numerous than their models
C. Because the Batesian mimic exploits a warning it does not back up
D. Because Batesian mimicry occurs only between insects of the same order

**Answer:** C. Because the Batesian mimic exploits a warning it does not back up

**Why:** One is a free rider, the other a shared investment. This is why Batesian mimicry is frequency-dependent, too many mimics and the signal stops working for anyone.

Page: https://tryals.app/practice/psychology-i/predator-prey-interactions/a-harmless-hoverfly-mimicking-a-wasp-is-batesian-several-toxic

### 7. Under the Red Queen hypothesis, a prey species that stops evolving new defences will hold its ground as long as the predator does not improve.

**Answer:** False

**Why:** False. The point of the metaphor is that competitors and parasites keep evolving, so standing still means falling behind, you must run to stay in the same place. It is the leading explanation for why sexual reproduction persists despite its twofold cost.

Page: https://tryals.app/practice/psychology-i/predator-prey-interactions/under-the-red-queen-hypothesis-a-prey-species-that-stops-evolving