Physiology 3: Body sizing and scaling Flashcards
Define allometry
Body parts grow at diff rates
Define isometry
Body parts grow at same rate
What is size important for?
Metabolism
Homeostasis
Growth
Reproduction
Larger animals have a _____ SA:V
smaller
Larger animals tend to:
Move ____ ____
_____ digestion rates
_____ respiration rates
Lose heat to the environ ___ quickly
Lose water to the environ ___quickly
more slowly
Slower
Slower
less
less
Define ontogenetic allometry
Body proportions change with development e.g baby’s head is much larger in proportion to adults
Define isometric scaling
Body proportions stay the same with development, quite unusual e.g froglets to frogs
Define static allometry
Body proportions differ between individuals of the same age and sex within a species. Often seen in sexually selected traits
Define evolutionary allometry
Body proportions between individuals of different species
Describe the equation used to describe allometric relationships
y = ax^b
y = size of body part
X = measure of whole body size
a = an initial growth index (size of y when x = 1)
b = scaling exponent. Proportional change in y per unit x
On an allometric relationship graph, what does it mean if b = 0, and what will the line look like?
There’s no relationship between size of body part and body size
= line is flat
On an allometric relationship graph, what does it mean if b = 1, and what will the line look like?
isometry
= positive straight line
On an allometric relationship graph, what does it mean if b = <1, and what will the line look like?
is b is less than 1 means negative allometry
= non linear curve (x increases at a greater rate than y)
On an allometric relationship graph, what does it mean if b = >1, and what will the line look like?
if b is greater than 1 means positive allometry
= non linear curve (y increases at greater rate than x)
On an allometric relationship graph, what is on the x and y axis?
x = body size
y = allometric trait (e.g body part, physiological trait)
On an allometric relationship graph what happens if the units for x and y aren’t the same?
If units are not the same for x and y, the value of b that represents isometry changes (its not b = 1)
What linearises the relationship on an allometric graph?
using a log-log scale
log y = log a + log x
Give an example showing the importance of units when looking at allometric relationships
Length of body trait vs surface area body
Linear dimension (m1) vs square dimension (m2)
So, isometry = m1/m2 = 0.5
b = 0.5 (new isometric description)
What is the problem with isometry (in terms of scaling)?
SA doesn’t scale at the same rate as volume
So, f you scale things purely linearly, the weight loading per each limb will increase
Describe the square cube law in isometric scaling
Isometric doubling of length will increase SA fourfold and vol (thus mass) eightfold
- Organism has 8x mass to support but area to support weight increases 4x
- Organism has 8x metabolically active tissue to support, but respiratory surface areas only increase 4x
What type of relationship is metabolic rate vs body size?
negative allometry
Give 1 reason why the relationship between metabolic rate and body mass not isometric?
Partly due to bigger animals losing less heat (due to larger SA:V), so can be less metabolically active
Why do marine mammals have a higher metabolic rate compared to terrestrial mammals?
they lose heat faster due to being surrounded by water
Why do larger animals have a lower metabolic rate when compared to body size than smaller animals?
The relationship between respiratory systems scales in terms of SA:V
Larger animals unable to get as much energy from their environ for the proportional amount of body mass they have
