Q.12 Identify the rule that suggests that the endothermic animals from cold climates
tend to have shorter extremities (ears and limbs) compared with animals from warmer climate.

1. Bergmann’s rule
2. Allen’s rule
3. Bottleneck effect rule
4. Survival of fittest

   Allen’s rule states that endothermic animals from cold climates evolve shorter extremities like ears and limbs to minimize heat loss, unlike those from warmer climates with longer appendages for heat dissipation.​

   Question Breakdown

   This tests ecogeographical rules explaining animal adaptations to climate via thermoregulation. Endotherms maintain body heat, so body shape optimizes surface-area-to-volume ratio.​

   • Bergmann’s rule: Larger body size in colder climates for heat conservation (overall mass, not extremities).

   • Allen’s rule: Shorter appendages (ears, limbs) in cold climates to reduce exposed surface area.

   • Bottleneck effect: Genetic drift from population crashes, unrelated to morphology.

   • Survival of fittest: Darwin’s natural selection principle, too broad.

   Option Analysis

   Option	Describes	Correct?	Reason
   Bergmann’s rule	Body size variation by climate	No	Focuses on overall size, not extremities ​.
   Allen’s rule	Shorter extremities in cold	Yes	Matches exactly: ears/limbs shorter for heat retention ​.
   Bottleneck effect	Genetic loss in small populations	No	Population genetics, not adaptation ​.
   Survival of fittest	Natural selection mechanism	No	General principle, not specific rule ​.

   Allen’s rule endothermic animals cold climates shorter extremities is a key ecogeographical principle for GATE Life Sciences ecology section. This PYQ solution details how cold-adapted animals like polar foxes have stubby ears/limbs to conserve heat.

   Allen’s Rule Explained

   Formulated by Joel Asaph Allen (1877), it predicts low surface-area-to-volume in cold via compact appendages. Warm-climate animals (e.g., desert foxes) have long ears for cooling. Driven by natural selection for thermoregulation.

   Real-World Examples

   • Arctic foxes: Tiny ears vs. fennec foxes’ huge ears.

   • Northern vs. southern rabbit breeds.​

   Solved PYQ

   Correct: Allen’s rule—shorter extremities minimize heat loss in cold.​

   GATE Prep Tip

   Link with Bergmann’s (body size). Practice: Cold = compact shape for endotherms.