Fiddler Crabs🦀 & Babies👶🏽


To begin, Allometry is the growth of portions of the body at different rates. In order to have a negative allometry, one body part should continue to increase, while another part of the body begins to decrease. To have positive allometry there should be two body parts that increase over time together.

After completing the Desmos activity there is an example for both negative and positive allometry. The example of a positive allometry is the fiddler crab claw size was compared to its body growth over time. Which was positive being that the claw and body both increase in size as it matures? The example for negative allometry is a human’s head and body growth. Given that the head of a baby’s head is bigger than it’s body, as the baby matures the head shrinks and the body grows.

An example of a power function used to depict allometry is the power function formula f(x)=kx^p. An example of this formula working in an allometry scenario is the growth of a body and its metabolism. For this creature, the formula used to figure if it is a negative or positive allometry is 4.14(x)^0.66= M(b) (for the growth of the metabolism) and  M(b)/x= y (for the growth of the creature’s body). This creature is an example of negative allometry. Because of the metabolism increases, while the body decreases over time. Here is the formula plugged in with numbers 2 &3 below…

4.14(2)^0.66 = 6.54154206223
6.54154206223/2 = 3.27077103111

4.14(3)^0.66 = 8.54870575972
8.54870575972/3 = 2.84956858657


What other examples can you find for allometry? Is the example a negative or positive example of allometry?


3 Comments Add yours

  1. Allometry can occur in most living organisms,such mouses,elephants,cats and etc. The size does not matter, the body is till growing to certain age depending on gender and the brain is still developing but the heart does not grow. Its the size of your fist. These organs do not grow in proportion. The picture above would be a positive allometry.


  2. I like the way you compared the Allometry to the humans head. The head is big when you’re a baby but as you grow it shrinks with is the definition of Allometry. I’m not sure but I think that the sigh of the coefficient of the power function matters when talking about the allometry. I also would like to have more in class activities about this topic.


  3. Dr. Fisher says:

    This is a great explanation of allometry! One thing to note: you state that “In order to have a negative allometry, one body part should continue to increase, while another part of the body begins to decrease.” It’s not that one body part shrinks. It’s that it grows slower than the other body part. For example, a baby’s head is smaller than an adults head. Our heads don’t shrink as we grow; they just grow slower than the rest of our body.

    Having said that, I really enjoyed reading your post, and I think you did a great job connecting allometry to power functions.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s