Risk compensation (Peltzman effect)

Biological Parallel

Armor doesn't reduce death—it just changes how you die. Three-spined sticklebacks with heavy lateral plate armor forage in open water where predators hunt, while low-armored morphs hide in vegetation—yet armored fish show higher parasite loads from trophically transmitted parasites in their riskier foraging zones. Hermit crabs occupying thin-walled *Cerithium atratum* shells face 27.3% higher predation than those in thick-walled *Tegula viridula* shells, yet continue selecting the thinner shells when foraging in high-resource exposed areas—demonstrating life-history trade-offs between protection and foraging access. Freshwater snails (*Helisoma trivolvis*) reduce feeding rates under predation risk but compensate by selecting microhabitats with higher resource density—phenotypic plasticity allows trading foraging efficiency for perceived safety. Even heavily armored lobsters hide during their 7-day soft-shell molting window, showing predator-deterrence fails when protection is temporarily lost. The pattern: organisms with better defenses take compensating risks through risk-sensitive foraging, with responses corresponding to perceived safety rather than actual survival probability. Protection from one threat class (predation) permits vulnerability to different threats (parasites, shell-crushing predators)—defense enables riskier foraging, which reallocates rather than eliminates mortality risk, following predator-prey dynamics.