predator-prey relationships

Predators evolve to become better hunters → Prey evolve to better avoid detection or escape.
Selection pressures lead to adaptations in both predators and prey.
Example: Transparent Deep-Sea Squid (Glass Squid)
- Collected from 800m depth.
- Highly transparent → Prevents forming a silhouette against downwelling light.
- Red-tinted stomach prevents detection by bioluminescent searchlights.
- Reflective structures around the eyes reduce visibility.

Camouflage can be divided into two major categories:

Category	Definition	Examples
Primary Defences	Prevent detection by predators.	Background matching, masquerade, countershading.
Secondary Defences	Reduce capture risk once detected.	Startle responses, eye spots, spines, venom.

Most intuitively simple form of camouflage.
Animals resemble their environment, blending in to avoid detection.
Challenges in defining "matching":
- Does an animal match spatial structure, colour, contrast, or texture?
- A species perfectly adapted to one background may be highly visible in another.
Examples:
- Moths, frogs, lizards with colour patterns that blend into tree bark or foliage.
- Cuttlefish dynamically adjust their skin pattern to match their background.
Experimental Evidence:
- Study on noctuid moths (genus Catocala) using blue jays:
  - Birds trained to peck at images of moths camouflaged on different backgrounds.
  - Higher detection success when moths were on non-matching backgrounds → Confirms background matching effectiveness.

Breaks up an animal's body outline, making detection harder.
Predators use edge detection to identify prey, so high-contrast patterns interfere with this.
Example:
- A fish with bold vertical bands that break up its body shape.
Experimental Evidence:
- Artificial Moth Experiment (Stevens et al., 2005)
  - Paper moths with different patterns pinned to tree bark.
  - Birds foraged on these "moths," revealing that disruptive patterns along the body edge significantly increased survival.

Darker dorsal (top) side, lighter ventral (underside).
Balances out self-shadowing, making animals appear flatter and harder to detect.
Common in terrestrial and aquatic animals.
Examples:
- Deer, fish, seabirds.
- Sharks and marine fish exhibit countershading, though possibly for different reasons.
Experimental Evidence:
- Artificial Caterpillar Study (Rowland et al.)
  - Pastry caterpillars dyed to mimic different shading patterns.
  - Countershaded models had higher survival than non-countershaded ones.

❌ Myth: Countershading prevents silhouettes when viewed from below.

Refuted by physics: Light from above is always brighter than a white ventral surface.
Only true silhouette reduction happens in bioluminescent animals (e.g., midwater fish).

Natural selection should favour the best camouflage → So why do some species maintain multiple morphs?
Answer: Apostatic Selection (Negative Frequency-Dependent Selection)
- Predators form a search image for common morphs, ignoring rarer ones.
- When one morph becomes too common, it experiences more predation, keeping variation stable.
Examples:
- Shoal Crabs: Juveniles display a variety of colour patterns.
- Grouse Locusts: Different morphs coexist despite predation.
Experimental Evidence:
- Herring Gull & Crab Experiment
  - Predators targeted the more common morph, shifting preference when another morph became dominant.

Unlike camouflage, which prevents detection, masquerade prevents recognition.
Animals resemble inedible or unimportant objects, even if fully visible.
Examples:
- Twig caterpillars resemble sticks.
- Leaf insects mimic leaves.
- Nudibranchs blend into coral reefs.
Key Research (John Skelhorn, Newcastle University):
- Predators actively misidentify masquerading prey as inedible objects.

Predators evolve better detection skills → Prey evolve better defences.
Camouflage, disruptive colouration, and countershading all help prey avoid detection.

Apostatic selection ensures polymorphism persists by creating frequency-dependent predation.