ANT333Y1 Lecture Notes - Lecture 19: Folivore, Ontogeny, Allometry

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ANT333 Lecture #19 Effects of Body Size
Size and Shape
Gould (1974) “Yet, however much we celebrate diversity and revel in the peculiarities of animals, we
must also acknowledge a striking “lawfulness” in the basic design of organisms. This regularity is
most strongly evident in the correlation of size and shape.”
Uniform body size in all mammals
Shape
Above a certain size, large terrestrial oganisms look basically alike - they have thick legs and
relatively short, stout bodies
An organism assumes a form best adapted to its size
In other words, point here is, that size may influence morphology, ecology, physiology and evolution
of an organism
Small vs. Large Organisms
Under identical physical forces but they are differentially affected.
Cohesion force that holds things together
Gravity pulling down force
Kinetic energy of motion
Modes of growth
Relative weakness of gravitational forces also permits a mode of growth that large animals could
not maintain
Insects discard their external skeleton & secrete a new one
A large mammal without any supporting structures would collapse to a formless mass under
influence of gravitational forces during a molt
The Effects of Size
There are 2 factors to consider with respect to body size:
o Surface area (length x width) &
o Volume (length x width x height)
The Effects of Size
As body size increases, surface area changes as function of square of linear dimensions (L2).
Two (2) dimensions that change in size: length x width.
The Effects of Size
As body size increases, body volume changes as function of cube of linear dimensions (L3).
Volume changes in three (3) dimensions: length x width x height.
If an animal were to double in length, breadth, and width, its cross-sectional dimensions would
increase 4x, and its volume would increase 8x
Size and Weight
Strength of bones is function of cross-sectional area of bone.
Animal whose linear dimensions doubled would weigh 8x as much
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Ant333 lecture #19 effects of body size. Gould (1974) yet, however much we celebrate diversity and revel in the peculiarities of animals, we must also acknowledge a striking lawfulness in the basic design of organisms. This regularity is most strongly evident in the correlation of size and shape. Above a certain size, large terrestrial oganisms look basically alike - they have thick legs and relatively short, stout bodies. An organism assumes a form best adapted to its size. In other words, point here is, that size may influence morphology, ecology, physiology and evolution of an organism. Under identical physical forces but they are differentially affected. Cohesion force that holds things together. Relative weakness of gravitational forces also permits a mode of growth that large animals could not maintain. Insects discard their external skeleton & secrete a new one. A large mammal without any supporting structures would collapse to a formless mass under influence of gravitational forces during a molt.

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