The Importance of Size

1
The Importance of Size

• Body Size and its Relationship to Mammalian Life
  History

2
Geometric Scaling Rules

• Scaling of Length, Area and Volume
• Area is proportional to L2
• Volume is proportional to L3
• So, doubling the length increases the area by a
  factor of 4 (22)and the volume by a factor of 8
  (23)
• Also, halving the length decreases the volume by
  a factor of 1/4 (1/2)2 and the volume by a
  factor of 1/8 (1/2)3

3
Scaling of Physiology

• Muscle strength is determined by cross-sectional
  area of muscle (L2), but
• Mass is determined by volume (L3)
• So, increase in size often requires changes in
  shape to accommodate these scaling relationships.
• For example, a gorillas femur is much thicker
  than a marmosets femur simply scaled up to
  gorilla size.
• Gorilla also has bigger muscles than a scaled up
  and proportional marmoset would have

4
Size and Life History

• Body size is strongly correlated with many life
  history traits of organisms
• Longevity and age at first reproduction ()
• Nutritional and energy requirements (-)
• Brain size (), litter size (-), gestation ()
• Home range size ()
• Susceptibility to predation (-)

5
Size and Diet

• Inverse relationship exists between body size and
  energy requirements, but larger primates eat more
  food daily
• Small primates need high energy diet, typically
  insects (insectivores)
• Large primates can make do with low energy diet,
  typically leaves, shoots and buds (folivorous)
• Frugivorous primates add insects or leaves to
  their diet (for protein), based on their body
  size

6
Size, Diet, and Energy

• Small primates must eat insects for their protein
  and energy (calories)
• They have relatively very high energy
  requirements
• Insects have much easily digested protein and are
  high in calories (per weight)
• Foraging time for sufficient insects is not
  excessive

7
Size, Diet, and Energy

• Large primates cannot eat insects for their
  protein and energy (calories)
• They dont have special adaptations that allow
  collection of sufficient quantity
• They have absolutely large daily food intake
  requirements
• Foraging for insects would take a large primate
  all day, and they would still starve!

8
Size, Diet, and Energy

• Small primates cant get their protein from
  leaves
• Leaves are low quality source of protein
• Difficult to digest cellulose without special
  enzymes or bacterial gut flora
• Full of toxins to discourage mammals from eating
  them
• Large primates have gut flora in separate
  chambers, long transit time due to long
  intestines, and lower relative energy
  requirements
• Large primates often subsist on fruit and leaves
• Some of the largest are obligate folivores

9
Size, Teeth, and Diet

• Molar tooth morphology can be used to determine
  diet of primates
• Eating fruit requires crushing while eating
  insects and leaves requires shearing
• Crushing leads to low, blunt cusps and large
  basins
• Shearing leads to sharp and long shearing crests
• Kays threshold of 500g seems to form a natural
  break between insectivores and folivores
• Kay measured shearing crests to distinguish
  between insectivorous, frugivorous, and
  folivorous primates

10
Size and Locomotion

• Body size has a tremendous influence on locomotor
  patterns among primates
• Constraints of body size involve mechanical
  forces involved in locomotion (i.e., gravity) and
  available platform sizes (i.e., arboreal vs.
  terrestrial)
• Suspensory behaviors are always practiced by
  large primates
• Leapers are always small
• Terrestrial primates are bigger than arboreal
  ones
• Quadrupeds can be any size

11
Regression Analysis

• If we can empirically determine the relationship
  between some anatomical variable and body size,
  we can estimate body size from fragmentary fossil
  remains using linear regression

Y mX b
Formula for line, m is slope and b is Y-intercept