BIOD43H3 Lecture Notes - Lecture 2: Allometry, Fossorial, Approximation Error
Tutorial 2:
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Stress scope indicates how much stress can be resisted by a loaded bone. Measurements of
limb bone stress in a variety of mammals during locomotion have shown that, within each gait,
the forces applied over bones increase proportionally with speed. Animals with greater stress
scope values should be able to attain greater speeds than animals with a lower stress scope.
Answer:
If locomotor performance in large mammals is constrained by the ability of musculoskeletal
structures to withstand forces during activity, it is expected that absolute maximum running
speed would be proportional to stress scope and therefore would scale according to Mb–0.27.
Consequently, a length-based measurement of performance would scale in proportion to Mb–
0.60.
• According to the geometric similarity principle, body length scales with mass proportion
to Mb -0.33.
• Relative running velocity scale as -> Mb – 0.27 + Mb 0.33 = Mb – 0.60
o Need to consider this relationship of stress scope and body length
2. The author warns that data on the running speed of animals may be of aiale ualit.
He then states that the magnitude of errors will be larger in small ranges of body mass than
in large ones. How can he conclude this?
He says that there are potentially some errors associated with the analyses because some
values have been estimated or measured with poor-precision methods. These errors will be
larger in small ranges of body mass than in large ones. Recompiled data were used, sacrificing
precision for completeness, hence quantity over quality.
Assuming there is no systematic bias in measurements, the analyses would underestimate the
real relationships between relative speed and Mb. When more than one value had been
reported for the same species, the single fastest running speed documented was chosen in an
attempt to reduce the effect of differences in procedure and/or motivation among studies.
Answer:
• In smaller animals, the error is going to be higher, less precision as you increase body
size
• The precision with which we can measure variation in speed increases with increasing
speed.
• Since larger animals tend to run at greater absolute velocities, relative error would be
less in these groups than in smaller animals.
3. Why were arboreal and fossorial species excluded from analyses?
These species have highly specialized habits and limb morphologies. 1975a). There are
significantly different allometric exponent for the limb bones dimensions (diameter and length)
of rodents and insectivores from those expected under elastic similarity, mainly due to limb
adaptations to their habitat.
Selective forces that shape their limb structures are different from those that shape variation
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Document Summary
Stress scope indicates how much stress can be resisted by a loaded bone. Measurements of limb bone stress in a variety of mammals during locomotion have shown that, within each gait, the forces applied over bones increase proportionally with speed. Animals with greater stress scope values should be able to attain greater speeds than animals with a lower stress scope. Consequently, a length-based measurement of performance would scale in proportion to mb . He then states that the magnitude of errors will be larger in small ranges of body mass than in large ones. He says that there are potentially some errors associated with the analyses because some values have been estimated or measured with poor-precision methods. These errors will be larger in small ranges of body mass than in large ones. Recompiled data were used, sacrificing precision for completeness, hence quantity over quality.
