Phys Eco Exam 2 Section 2: Metabolic Rate & Body-Size Scaling

What is metabolic rate?

The overall use of chemical energy by an organism, including oxidation of food to produce ATP.

What do most maintenance metabolic-rate measurements exclude?

Digestion.

What is specific dynamic action?

Metabolic heat produced through digestion, including fermentation.

What affects specific dynamic action?

Diet composition and meal size. It occurs in all animal groups.

What is basal metabolic rate (BMR)?

Minimum metabolic rate of an endotherm that is not moving, digesting, or thermoregulating.

What is resting metabolic rate (RMR)?

Metabolic rate of an endotherm that is not moving or thermoregulating.

When is RMR used instead of BMR?

For animals that cannot tolerate fasting.

What is standard metabolic rate (SMR)?

Metabolic rate of an ectotherm that is not moving or digesting, measured at a specific body temperature.

Why must temperature be specified for SMR?

Ectotherm metabolic rate changes with body temperature.

What is scaling?

Examining the consequences of changes in body size.

How can body size be measured?

Linear dimensions such as length/height or mass/weight.

What is an isometric relationship?

A relationship directly proportional to body size.

What is an allometric relationship?

A relationship not directly proportional to body size.

How are scaling relationships usually displayed?

On logarithmic scales, often log-log plots.

How can body-size energy requirements be expressed?

As whole-animal or mass-specific energy requirements.

How do whole-animal and mass-specific energy needs relate to body size?

Both have allometric relationships with body size.

What does the slope of a log-log scaling relationship represent?

The exponent of the scaling relationship.

How does whole-body maintenance O₂ consumption scale with body mass?

Exponent of approximately 0.65–0.75, averaging 0.70 across species.

How does mass-specific O₂ consumption scale with body mass?

Exponent of approximately −0.3.

How widely does metabolic scaling occur?

Across vertebrates, invertebrates, endotherms, ectotherms, and even plants.

How do energy requirements differ between small and large animals?

Small animals require more energy per unit body mass.

How does gut capacity scale in small mammals?

Isometrically, so gut capacity per unit body mass remains similar.

What digestive advantages do larger animals have?

More room for digestion, more energy available for storage, and the ability to eat poorer-quality food.

Why must smaller animals eat higher-quality food?

Their mass-specific energy requirements are greater.