What limits the size of animals? (Chapter 1)
Ability to support static load – bone diameter, compressive strength
Availability of food that is of high energy value and rapidly digested
We see in Chapter 2:
- Dimensions
- Material
- Design
- Not Oxygen (does not seem to constrain body size because tracheas in insects can support
larger size, but we do not see larger size insects)
We see in Chapter 3:
- Speed
Chapter 2
Scaling deals with the structural and functional consequences of changes in size or scale among
otherwise similar organisms.
- Tension – all forces are pulling away from the object
- Compression – forces acting on the material push towards the body
Two measurements: mass and linear dimension
Mass is an important consideration for:
- Strength of supporting structures (skeletons)
- Demands on the muscular system in locomotion
- Need for food
Convection is fluid flow that occurs due to effects of material property heterogeneity and body forces on
a fluid (gas or liquid), most commonly density (incl heat) and gravity
Oxygen – mass transport by convection, hemoglobin and circulation (mammals), diffusion in gas
(tracheae in insects). Oxygen transportation does not seem to constrain body size. Tracheas in insects
can support larger sizes, but we do not see larger sizes
Isometric = geometrically similar = well-defined concept of geometric similarity
As the volume of a body is increased, its surface does not increase in the same proportion = rather, in
proportion to the two-thirds power of the volume
- (relative) Surface area per unit volume decreases with increasing volume
23 cube = surface area is 24, volume is 8. 24/8 = 3
Ability to support static load – bone diameter, compressive strength
Availability of food that is of high energy value and rapidly digested
We see in Chapter 2:
- Dimensions
- Material
- Design
- Not Oxygen (does not seem to constrain body size because tracheas in insects can support
larger size, but we do not see larger size insects)
We see in Chapter 3:
- Speed
Chapter 2
Scaling deals with the structural and functional consequences of changes in size or scale among
otherwise similar organisms.
- Tension – all forces are pulling away from the object
- Compression – forces acting on the material push towards the body
Two measurements: mass and linear dimension
Mass is an important consideration for:
- Strength of supporting structures (skeletons)
- Demands on the muscular system in locomotion
- Need for food
Convection is fluid flow that occurs due to effects of material property heterogeneity and body forces on
a fluid (gas or liquid), most commonly density (incl heat) and gravity
Oxygen – mass transport by convection, hemoglobin and circulation (mammals), diffusion in gas
(tracheae in insects). Oxygen transportation does not seem to constrain body size. Tracheas in insects
can support larger sizes, but we do not see larger sizes
Isometric = geometrically similar = well-defined concept of geometric similarity
As the volume of a body is increased, its surface does not increase in the same proportion = rather, in
proportion to the two-thirds power of the volume
- (relative) Surface area per unit volume decreases with increasing volume
23 cube = surface area is 24, volume is 8. 24/8 = 3
