BIO2242 Lecture Notes - Lecture 15: Allometry, Vacuum Cleaner
Lecture 15 – Animal Sizing and Scaling
• Size has strong influence on way animals interact with environment
• Mass influences a great many physiological, ecological and life history
variables
• Y = a Xb
o Trait of interest = constant x body masssomevalue
• If power (b) is 1 – relationship is isometric
• If power is b>/< 1 – relationship is allometric
o Use equation to tell us merging properties of
organisms of different size
• Problem: 90% of mammals weigh less than 23 kg → log
o Log transformation makes all lines linear
o Exponent less than 1 = Allometric
o If organism doubles in size (1kg → 2kg), metabolic rate increases by
factor less than 2
▪ Increases more slowly than mass
The Importance of Allometry
• Whole animal metabolic rate is the metabolic rate of an animal
• Mass specific metabolic rate is the metabolic rate per unit of body mass (MR
divided by mass)
• MR = amb
o If b is less than 1, mass specific metabolic rate decreases with mass
• As fish size decrease, mass specific energy rate increases
• Small fish with high mass specific metabolic rate, can only have fewer of
them
o Total biomass of fish left have to be lower
• Changing size distribution of species within environment, changing amount of
biomass that environment can support
o Higher populations → smaller amounts of biomass
• Metabolic rate important for dictating how much food they eat → Allometric
principles how much that is in population scale
Influence of Size on Blood Pressure
• Animals have to work against gravity
• The further heart has to pump blood, greater the pressure
o The higher the distance between the heart and the
target of blood – the greater of the pressure that’s needed
Allometric Scaling
Isometric
• Other than metric
• Not direct proportionality between function
and body size
o E.g surface area
• Graph: increase less or more
• E.g. Skeletal mass, metabolic rate, heart
rate
• Same as metric
• Direct proportionality between function
and body size
• Graph: linear relationship
• E.g. blood volume of mammals
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