Metabolic Rate, Dormancy, and Body Temperature

Overview of Metabolic Rates

• Metabolic Rate: The rate at which organisms convert energy for biological functions.

• Fick Equation: Models the flow of oxygen in the body and scales with size, determining metabolic rates based on body size and heart rate.

Heart Rate and Metabolism

• Larger Animals: Exhibit lower heart rates and cardiac output compared to smaller animals.

• Oxygen Consumption: Measured during different locomotion types (swimming, running, flying).

• Power Equation: Represents the non-linear relationship between heart rate and oxygen consumption.

Data Transformation for Analysis

• Transforming Data: Logarithmic transformation aligns the data into a linear format, aiding in statistical analysis.

• Common Relationships: Suggests that species share similar relationships between heart rate and oxygen consumption.

Endothermic Animals and Temperature Regulation

• Endothermic Hibernators: Examples largely from mammals; show variation across species in how they respond to seasonal changes in temperature.

• Response Strategies:

  • Avoidance: Migration or hibernation minimizes exposure to harsh conditions.

  • Regulation: Actively spending energy to maintain body temperature.

  • Conformity: Ectotherms allow body temperature to fluctuate with the environment.

Heterothermy in Animals

• Heterothermy: The ability to regulate body temperature strategically.

  • Regional Heterothermy: Some body parts maintain different temperatures.

  • Timing: Daily or seasonal changes in body temperature to conserve energy.

• Examples:

  • Red Deer: Seasonal heart rate and body temperature changes; lower during winter to save energy.

  • Willow Tit: Mild hypothermia observed; able to survive cold nights.

Temperature Effects on Metabolism

• Q10 Effect: A 10°C change can significantly alter metabolic rates.

• Body Temperature Fluctuation: Small changes can save substantial energy (up to 40%).

Metabolic Strategies in Different Species

• Torpor vs. Hibernation:

  • Torpor: Shorter state of significantly lowered metabolic rates.

  • Hibernation: Extended periods of low metabolic rates, usually accompanied by deeper temperature drops.

• Examples of Daily Torpor:

  • Bats: Mexican free-tailed bats vs. big brown bats in hibernating strategies.

  • Hummingbirds: Exhibit nightly torpor due to temperature drops in mountainous tropical areas.

Physiological Differences in Hibernators vs. Torpid Animals

• Metabolic Rates: Hibernating animals display dramatically lower rates compared to torpid ones.

• Body Temperature: Lower average temperatures and duration of torpor/hibernation.

Costs of Arousal and Energy Saving Strategies

• Arousal Costs: Significant energy expenditure occurs during re-warming from torpor.

• Maintenance of Body Weight: Animals like the pocket mouse can maintain body weight on reduced food intake by entering torpor.

Summary of Thermoregulation Patterns

• Bergmann's Rule: Larger animals are typically found in colder climates due to advantages in heat conservation.

• Allen's Rule: Animals in colder climates tend to have shorter limbs and extremities to reduce heat loss.

• Cooling and Warming Rates: Larger animals take longer to cool and warm, affecting their strategies for entering torpor or hibernation.