Lecture 3: Body Size and Allometry

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Questions and Answers

Given a heart rate scaling exponent of -0.25, what would be the predicted approximate heart rate for a 2.5g pygmy shrew based solely on mass?

  • Approximately 3000 beats/min (correct)
  • Higher than 3000 beats/min
  • Lower than 1400 beats/min
  • Approximately 1400 beats/min

What physiological constraint limits the maximum heart rate of the pygmy shrew?

  • The rate at which cardiac muscle can contract (correct)
  • The metabolic rate of the animal itself
  • The size of the heart
  • The availability of oxygen to the heart muscle

According to the provided information, what is the approximate scaling exponent for heart mass in mammals?

  • 0.98 (correct)
  • -0.25
  • 1.0
  • 0.0059

Pronghorns are referred to as an “informative exception” in the context of allometry, why?

<p>They exhibit a unique scaling relationship. (A)</p> Signup and view all the answers

Why does the scaling exponent for lung mass differ from the scaling exponent for VO2max (aerobic capacity)?

<p>Lungs perform functions beyond oxygen exchange, such as thermoregulation and excretion of waste gasses. (B)</p> Signup and view all the answers

What is the primary distinction between isometry and allometry in the context of biological scaling?

<p>Isometry implies that body proportions remain constant with changes in size, while allometry means body proportions change with size. (A)</p> Signup and view all the answers

In the equation for basal metabolic rate (BMR), M = aW^b, what does the term 'b' represent?

<p>The mass exponent, reflecting how metabolic rate scales with body mass. (B)</p> Signup and view all the answers

Which of the following best describes the relationship between body size and BMR as suggested by the scaling equation M = aW^b?

<p>BMR scales with body mass through an exponential function where 'b' dictates the rate of change. (D)</p> Signup and view all the answers

What is the primary purpose of using logarithmic scales when analyzing allometric relationships, such as the one between body size and basal metabolic rate?

<p>To better visualize highly non-linear relationships as straight lines on a graph. (A)</p> Signup and view all the answers

What does the term 'allos' (from the Greek language) signify in the context of allometric changes in animal body proportions?

<p>Different or varied, reflecting a change in proportions. (C)</p> Signup and view all the answers

If the relationship between log metabolic rate (log BMR) and log mass (log M) is given by log BMR = log 70 + 0.72 log M, what does the value 0.72 represent?

<p>The scaling exponent of the BMR to body mass relationship (A)</p> Signup and view all the answers

Given the equation M = aW^b, how is mass-specific metabolic rate (BMR/g) calculated based on the information provided?

<p>BMR/g = 70W^-0.28 (B)</p> Signup and view all the answers

According to the provided information, which of the following is the most significant reason for why the relationship between surface area (SA) to volume (V) of an animal does not fully account for the measured scaling of metabolism?

<p>Ectotherm metabolism also scales at approximately 0.75, despite different scaling relative to heat loss. (A)</p> Signup and view all the answers

What is the approximate scaling exponent (b) for Maximum Metabolic Rate (VO2 max) in the provided data?

<p>0.86, which is higher than the BMR exponent (C)</p> Signup and view all the answers

According to the information, what is a key characteristic of mammal heart mass scaling?

<p>Isometric, which means it scales proportionally with body mass (A)</p> Signup and view all the answers

In the context of the provided text, how would you best describe what the 'informative exceptions' are when considering scaling constraints in biological systems?

<p>Novel adaptations that arise to circumvent scaling limitations. (A)</p> Signup and view all the answers

Using the provided information, what does the value of 'a' represent in the equation log M = log a + b log W?

<p>The y-intercept of the log-log plot (B)</p> Signup and view all the answers

What is the best explanation of the term 'Semi-lucid' as used in the context provided of measuring VO2 max?

<p>A partially aware state of the measured subject, which is essential for these methods (A)</p> Signup and view all the answers

Flashcards

Physiological Allometry

The relationship between body size and a physiological trait. The trait can change with the body size. For example, a larger animal typically has a lower heart rate.

Allometry

The study of how different organisms change in proportion as they grow in size. Often it is not just a proportional change; it can be exponential.

Basal Metabolic Rate (BMR)

The rate of energy expenditure of an organism at rest. A baseline measurement of how much energy an organism needs to survive.

M = aWb

A mathematical relationship that describes how changes in size affect a particular trait. The exponent 'b' in this equation indicates the degree of allometric change. For example, if 'b' is 0.75, it means the trait increases 75% for every 100% increase in size.

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Isometry

When a trait changes proportionally with body size. For example, imagine a dog growing bigger while maintaining the same body proportions. The dog simply becomes larger.

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Heart rate scaling with body mass

The relationship between the heart rate of an animal and its body mass, where heart rate decreases as body mass increases. This relationship is typically represented by the equation: Heart rate = 241 M-0.25, where M is the body mass.

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Heart mass allometry

The phenomenon where the mass of an animal's heart does not scale proportionally to its body mass. For example, a pygmy shrew's heart is much larger than predicted based on its body mass.

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Cardiac muscle contraction limit

A biological constraint where the cardiac muscle can only contract at a maximum rate of 1,400 beats/minute. This limits the heart rate of small mammals, even though their metabolic demands would require a faster heart rate.

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Informative exceptions in allometry

A deviation from the expected scaling relationship between a physiological trait and body mass. This suggests that the animal has evolved unique adaptations to meet its metabolic demands. Example: The pronghorn has a higher heart rate than predicted based on its body mass.

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Metabolic Allometry

The relationship between body size and metabolic rate. It's usually described by the equation log M = log a + b log W, where M is metabolic rate, W is body mass, 'a' is the intercept, and 'b' is the slope (mass exponent).

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Mass Exponent (b)

The exponent in the allometric equation (log M = log a + b log W) that indicates how metabolic rate changes with body mass. A higher exponent indicates a greater increase in metabolic rate with increasing body size.

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Slope of the Allometric Line

The slope of the line on a log-log plot of metabolic rate vs body mass. It represents the mass exponent (b) in the allometric equation.

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Mass-Specific Metabolic Rate

The metabolic rate per unit of body mass. It reflects the energy expenditure required to maintain body functions at a given body size.

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Maximal Metabolic Rate (VO2max)

The maximum rate of oxygen consumption during strenuous exercise. It reflects the organism's ability to produce energy aerobically.

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Physiological Scaling

The study of how the scaling of physiological traits affects the evolution and ecology of organisms. For example, how the scaling of metabolic rate influences the distribution and abundance of species.

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Study Notes

Lecture 3: 10 Jan

  • Topic: Size matters: body size, allometry, and physiological allometry
  • Reading: Pages 19-20, 184-192, 230-233
  • Covered: Causes, exceptions, correlates, and implications
  • Lecture details: Body size, allometry, and physiological principles

Scope of Animal Size

  • Subtopics: How small? and How big?

Scope of Invertebrate Size

  • Subtopics: How small? and How big?

Scope of Mammal Size

  • Subtopics: How small? and How big?

Scope of Bird Size

  • Subtopics: How small? and How big?

Patterns of Size Change: Isometry

  • Proportions remain consistent despite changes in size.

Patterns of Size Change: Anatomical Isometry

  • Proportions remain constant as size changes, exemplified by images of growing organisms like salamanders and fish

Patterns of Size Change: Anatomical Allometry

  • Proportions change with size, exemplified by images of humans at different ages

Physiological Allometry: Linear Axis Scales, Basal Metabolic Rate (BMR)

  • Relationship between body weight and metabolic rate plotted.
  • Metabolic rate (M) is related to body weight (W) by the equation: M = aWb, where -a is a proportionality constant -b is the mass exponent

Log Axis Scales & Allometry: BMR

  • Data presented on logarithmic scales to better visualize relationships.
  • The relationship of metabolic rate to body mass is approximately linear when plotting on log-log scales for animals.
  • Equation: log BMR = log 70 + 0.72 logM
  • BMR = 70M0.72

Mass-Specific Allometry: BMR/g

  • Focus on the metabolic rate per unit body mass.
  • Equation: M/W = aW(b-1)
  • BMR/g = 70W-0.28.

Log Scales & Mass-Specific MR

  • Plotting metabolic rate and body mass on a log scale reveals a relationship close to linear.
  • Equation: log M = log a + b log W; log BMR = log 70 + 0.72 log M.

What "Causes" Metabolic Allometry?

  • Heat production within the animal's volume, exchange with the environment across the surface area (SA): Small animals lose heat more quickly over their larger surface areas.
  • SA/V ratio: This explains why small animals need high metabolisms to compensate for faster heat loss.

Ectotherm Scaling

  • Metabolic rates of cold-blooded organisms (poikilotherms) are plotted on a log-log scale, showing an approximate linear relationship.

Scaling of Maximal Metabolic Rate (VO2max)

  • Relationship between body mass and maximal oxygen consumption (VO2max).
  • Equation: VO2max scales with the body mass0.86

Measuring VO2max

  • Methods demonstrated by images, which could include: Measurements using equipment or animals/humans in special experiments

Informative Exceptions

  • Animals (e.g., pronghorn) whose data deviate from the typical scaling patterns.

Allometry of components of aerobic metabolism in mammals, most similar to VO2max

  • Discussion of factors influencing and complicating the VO2max scaling patterns

Mammalian Cardiac Scaling, Matching heart function to metabolic rate

  • Relationship between heart mass and body mass.
  • Heart mass scales isometrically with body mass (approximately M0.98).
  • Heart rate scales inversely with body mass (approximately M-0.25)

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