Math with Mammals

While tearing down an old fence along the treeline at a city park, and clearing the brush back for a new fence at an Eagle Project, we came upon this little creature:

It is a mammal, and one that people often misidentify as a mouse, or even a shrew.  Can you guess what it is?

In this photo, you can see the basic body shape.  It is fatter than a mouse, and has a shorter tail.  Also, its ears are smaller than a mouse's would be.

Yep!  It's a vole!

Voles are in the rodent family, which comes from the word rodere meaning "to gnaw" or "to eat away".  This is fitting because they have two very long teeth in front with which they do a lot of gnawing.

Violet the Vole

With voles we see an example of  exponential growth.

One female vole - let's call her Violet - can have up to 10 litters in a year.  Each litter can have between 5 to 10 pups.  So for Violet alone, that's a potential of having 50 to 100 pups in a year.  But that's not all.  Each pup matures to an adult vole in four weeks.  So a month after Violet's first litter, she is already expecting a new litter of 5 to 10 babies, and so are her offspring from her first litter.  As the year progresses, her children, grandchildren, great grandchildren and great greats are producing litters of their own.  Voila!  You have a veritable vole explosion.

Here's a partial breakdown:

Litter #1:
Violet has 5 to 10 pups.  We'll call these pups Generation #1.
Total:  5 to 10 pups

Litter #2:
Violet has 5 to 10 pups.
Generation #1 has 50 to 100 pups, called Generation #2A
Total Pups:  55 to 110

Litter #3:
Violet 5 to 10 pups.
Generation #1 has 50 to 100 pups, called Generation #2B
Generation #2A has 500 to 1,000 pups, called Generation #3A
Total Pups:  555 to 1,110

Litter #4:
Violet 5 to 10 pups.
Generation #1 has 50 to 100 pups, called Generation #2C
Generation #2 has 500 to 1,000 pups, called Generation #3B
Generation #2B has 500 to 1,000 pups, called Generation #4B
Generation #3A has 2,500 to 10,000 pups, called Generation #5A
Total Pups:  3,555 to 12,110

You can see where this is going.  With 6 more litters to go in the cycle of this theoretical year, it is easy to see that the number of pups produced will be ASTRONOMICAL!  And this is starting with only one vole.  But Violet was not born in a vacuum and has parents, siblings, cousins and grandparents of her own, all producing young at the same pace.

So why don't we see voles everywhere we go?  Well, they have natural predators who eat them up, and help keep their population in check.  Thousands of snakes, raccoons, hawks and owls dine on these tasty little beasties every day, and save us from being overrun.