Caloric Requirements for the Animals in Your Ecosystems

                                     Units Nine and Ten --- Land Ecologies

World Builders

What Do Food Pyramids Really Tell Us?

If we know the Primary Productivity of our plants, we can estimate how many animals that biome can support and what sizes those animals can be.

You should have described your animals in the Land Animals Assignment, including their weight.

For the purposes of this class we will assume that your animals have metabolic rates similar to our earthly animals, which means that under similar conditions they will need about the same number of KiloCalories per day. Of course, we do not know anything about the needs of the life forms on other worlds, although they, too, will need some energy.

Now let's figure out how many KiloCalories (food calories) your animals will need per day.

There is a law called Kleiber's Law which can help us with this. The Formula is

Kilocalories per day = K0.75 (BW)

This means that

the number of Kilocalories that your animal needs per day                                                = K0.75 multiplied by the Body Weight of the animal in kilograms.

1 pound = 0.45 kilograms
Multiply the number of pounds by 0.45 to get Kilograms

Now, let's do it! For an animal that weighs 5 pounds (a puppy, maybe)

Kilocalories per day for a 5 pound mammal =

K0.75   X  (5 pounds  X  0.45 to 
                 convert to Kilograms)

Find the type of animal from the chart below. Go to the last column on the right and get K0.75 .

Kilocalories per day for 5 pound mammal =

 K0.75 X  (weight in pounds  X  0.45)

 24.7  X  (5   X  0.45) =

 24.7  X  2.25  =  55.57

Choose Your Animal Type
Use this number
Reptile -- lizard, snake, turtle -- Cold Blooded Ectotherm
K = 10
Marsupial -- kangaroo, opposum -- has baby in pouch
K = 49
Placental Mammal -- dogs, cats -- baby grows in mother
K = 72
Non-passerine bird -- ostrich, chicken -- non-perching birds
K = 78
Passerine bird -- little perching birds -- robins, sparrows
K = 129
from: Patrick J Morris

NOTE "Cold blooded" animals that do not heat their bodies, (for example: lizards and crocodiles,) require many fewer calories per day than endotherms, who are "warm blooded". Warm blooded animals try to keep their bodies at a constant temperature, and this uses many Kilocalories.

The numbers above do not apply to very small animals such as mice and humming birds, that weigh less than half a pound,. These animals have a large surface area compared with their volume, and so lose a lot of heat.  They would need to eat many more KiloCalories.

Copyright © 1999, 2003. Elizabeth Anne Viau and her licensors. All rights reserved. This material may be used by individuals for instructional purposes but not sold. Please inform the author if you use it at