Topic 2 -Energy Expenditure: Body Size, Locomotion, and Reproduction

Chemical Energy

Energy stored in the bonds of food molecules that animals release through metabolism.

Bioenergetics

The study of energy relationships and transformations in living organisms.

Oxidative Phosphorylation

Process in which ATP is produced from energy sources via electron transport and oxygen.

ATP "Energy Battery"

Adenosine triphosphate stores readily usable energy in its terminal phosphate bonds.

Exergonic Reaction

Spontaneous, energy-releasing (−ΔG) reaction, typically catabolic.

Endergonic Reaction

Energy-consuming (+ΔG) anabolic reaction that builds complex molecules.

Activation Energy

Initial energy input required to push reactants into an unstable, high-energy state.

Catabolic Pathways

Metabolic routes that break molecules down to release energy, often captured as ATP.

Anabolic Pathways

Metabolic routes that build complex molecules and require energy input.

Gibbs Free Energy (ΔG)

Usable energy in a system; ΔG = ΔH – TΔS describes energy change of reactions.

Bomb Calorimeter

Device that measures food energy content by complete combustion.

Metabolism

Sum of all chemical reactions occurring within an organism.

Metabolic Rate

Heat energy released per unit time from all metabolic reactions.

Basal Metabolic Rate (BMR)

Energy expenditure of a resting, post-absorptive endotherm at a neutral temperature.

Stable Metabolic Rate (SMR)

Resting metabolic rate measured at a specified body temperature.

Field Metabolic Rate (FMR)

Metabolic rate of a free-living animal performing normal activities in the wild.

Calorie (nutritional)

Kilocalorie; energy to raise 1 kg of water 1 °C, used on food labels (abbrev. Cal).

Scaling Effects

How anatomical or physiological parameters change with body mass.

Isometric Scaling

Growth where proportions stay constant as size changes; governed by the square-cube law.

Square-Cube Law

If length doubles, surface area scales ×4 and volume/mass ×8, causing functional mismatches.

Allometric Scaling

Growth or evolution where proportions change with size, deviating from isometry.

Scaling Exponent

Power-law exponent describing how a trait varies with body mass (e.g., mass^0.75).

Kleiber’s Law

BMR scales to body mass^0.75; large animals have lower mass-specific metabolism.

Mouse-to-Elephant Curve

Log-log plot of BMR vs. mass illustrating Kleiber’s Law from small to large mammals.

Metabolic Cost of Locomotion

Extra energy (kcal kg⁻¹ km⁻¹) needed beyond BMR to move a unit mass a unit distance.

Cost of Transport

Energy required to move one kilogram of body mass one kilometer.

U-Shaped Cost Curve

Relationship where cost per distance decreases then rises as velocity increases.

Maximum Aerobic Velocity

Highest speed sustainable using aerobic metabolism before anaerobic pathways engage.

Anaerobic Respiration

Energy production without oxygen, yielding lactic acid and limited duration power.

Inertia

Resistance of a mass to acceleration or deceleration.

Momentum

Tendency of a moving mass to maintain velocity (mass × velocity).

Drag

Force opposing motion through a medium, increasing with surface area and velocity².

Reynolds Number

Dimensionless ratio of inertial to viscous forces predicting flow regime around bodies.

Laminar Flow

Smooth, parallel fluid layers over a surface with minimal mixing and turbulence.

Turbulence

Chaotic, mixed flow with rapid velocity gradients, increasing drag.

Fusiform Shape

Streamlined, torpedo-like body that promotes laminar flow and reduces drag.

Propulsive Thrust

Forward-directed force generated by muscles or wings during locomotion.

Lift

Aerodynamic force perpendicular to airflow that supports weight in flight.

Symmetrical Gait

Left and right limbs alternate in a regular pattern (e.g., walk, trot).

Asymmetrical Gait

Limbs move together, producing a suspended phase (e.g., gallop, bound).

Duty Factor

Percentage of stride cycle a foot stays in contact with the ground.

Forelimb-Hindlimb Phase

Timing relationship between fore- and hind-limb footfalls in a gait cycle.

Intermittent Locomotion

Energy-saving strategy inserting rest or glide phases between active movement bursts.

Endotherm

Animal that generates metabolic heat to maintain a stable internal temperature.

Ectotherm

Animal whose body temperature and metabolism largely track external temperatures.

Circadian Rhythm

Endogenous, entrainable ~24-hour biological cycle in physiology or behavior.

Free-Running Period (τ)

Length of a circadian cycle under constant conditions, usually ~24 h.

Entrainment

Resetting a biological rhythm to match an external cycle (e.g., light-dark).

Zeitgeber

External “time-giver” cue (light, temperature) that synchronizes circadian rhythms.

Temperature Compensation

Ability of circadian clocks to keep ~24 h period despite temperature changes.

Q10 Temperature Coefficient

Ratio of reaction rates over a 10 °C range; ≈1 indicates temperature compensation.

Ultradian Rhythm

Endogenous cycle with a period shorter than 24 h (e.g., heartbeat, REM cycles).

Infradian Rhythm

Endogenous cycle longer than 24 h (e.g., menstrual, seasonal).

Circalunal Rhythm

Biological cycle synchronized to the ~29.5-day lunar month.

Circatidal Rhythm

Endogenous ~12.4-hour cycle aligned with tidal periods.

Circannual Rhythm

Year-long endogenous cycle governing seasonal behaviors (molting, breeding).

r-Selection

Reproductive strategy emphasizing many low-investment offspring and high growth rate.

K-Selection

Strategy investing heavily in few offspring with high survival probability.

Gametogenesis

Production of gametes; eggs are typically energetically costlier than sperm.

Parental Care Energetics

Energy costs associated with nurturing and protecting offspring after birth or hatching.

Lactation Cost

Energy (often ≥40 % of budget) required by mammals to produce milk for young.

Nest-Building Cost

Metabolic and time expenditure to construct shelters for eggs or offspring.

Thermogenesis

Metabolic heat production used by endotherms to maintain body temperature.

Torpor

Daily short-term controlled reduction in body temperature and metabolism.

Hibernation

Extended seasonal torpor with greatly reduced metabolism and temperature.

Buoyancy (Aquatic)

Upward force in water reducing weight support costs for aquatic animals.

Power-to-Drag Ratio

Measure of swimming performance; higher ratios allow greater speed.