Alien Bodies

Lesson 11

Food and Food Gathering or Capture

What do your aliens eat, and how do they obtain their food? How do they get the food inside their bodies? Do they break it up somehow to make it easier to digest?

The snorvep eats little, soft-bodied slug-like creatures. It captures them with its long tongue and swallows them whole.

Food Requirements, Metabolism, and Body Size

• endotherms (animals that burn energy to heat up their bodies, like cats) or
• ectotherms (animals that get their body heat from the environment, like lizards)?

Do your aliens eat meat, plants, or a combination to get the energy that they need?

On earth, the wawrm-blooded endotherms need about ten times as many calories as cold blooded ectotherms that have the same weight. Use the Some Animal Weights and Caloric Requirements on Earth chart to figure out how much food your animals need to eat each day.

For example, the snorvep is cold blooded and weighs about 8 pounds. I see that a warm-blooded animal that weghs 8 pounds needs about 40 calories per pound per day.

8 pounds * 40 calories = 320 Kilocalories a day

A snorvep is cold-blooded, so we divide

320 Kilocalories for an endotherm (warm blooded animal)   = 320   =    32 KiloCalories
10                                                    10

Following the Energy Trail

The snorvep eats little slugs that are just about all meat. However, we know that, at each step of a food pyramid, only 10% of the energy goes to the next level. The rest of the energy is used up in keeping the body repaired, movement, digestion, and reproduction. (In warm blooded animals, energy is also used in heating the body.)

If the snorvep eats 32 KiloCalories a day, we can multiply by 10 and figure that the slugs eat 320 KiloCalories a day.

The slugs are herbivores, so they eat plants. But once again, only 10% of what they eat becomes the bodies of the herbivores. So the plants actually need 3,200 (320  times 10 KiloCalories of plant captured solar energy) KiloCalories to live and grow.

For simplicity's sake. I am going to assume that the solar radiation received by the snorvep's planet is the same as what we receive on earth. When we go to the page called Following the Energy Trail we see that, at the equator, the ground receives a maximum of about 3000 KiloCalories per square meter (close to a square yard) of solar energy in each 24 hour day. However, only about 30 KiloCalories actually get turned into plant biomass because plants don't turn it all into plant tissue

So if the slugs need 3200 KiloCalories of plant biomass a day, and the plants produce growth containing 30 KiloCalories per square meter a day, we will need to do a little more simple math:

Slugs need 3200 KiloCalories per day of plant biomass      = 3200 = 290 meters squared per snorvep
Plants produce 30 KiloCalories per day per meter squared        30

However, the planet is very cloudy, foggy, and wet, so I would guess that only about a half of the sun's energy actually gets down to the plants. That means that it will take twice as many meters squared to produce the necessary food.

2 *290 meters squared= 580 per day

Let's round this up to 600 square meters a day.

Now, what will the snorvep eat tomorrow? Well, it takes about 90 days for the slugs to grow from eggs to reproducing adults. The snorvep will need 600 square meters times 90 days of space to eat regularly.

600 times 90 = 54,000 meters squared.

This is a square about 232 meters to a side. (We find this by taking the square root of 54,000.  Use a calculator.)

A kilometer is 1000 meters long.
(A Kilometer is about two thirds of a mile.)

Under ideal growing conditions, each snorvep needs a space about 50 meters square.

I have represented the area needed by one snorvep under ideal conditions by coloring a square green.

However, real life is not ideal. There will be rocks and puddles of water in the plant area, and and passing animals will break some of the plants as they go by. Let's double this growing area (green diagonal lines).

Ranchers say of pasture, "Take half and leave half." They mean that allowing extra space will ensure that their animals are well fed and the pasture undamaged and able to grow back. It is important to "walk lightly on the land", to be sure that whatever resource is consumed has the opportunity to regenerate itself. For example, if the snorvep eats all the slugs in its feeding area it will wipe out its own food source. Some slugs musts be left to be the parents of a new generation. The level of use that can be continued indefinitely is called the carrying capacity of an environment. I have put pink diagonal lines in the diagram to represent the carrying capacity of the snorvep's environment.

Each snorvep has been assigned a space that is 100 meters on each side.

100 meters times 100 meters = 10,000 square meters.

In a square kilometer (1000 meters to a side, so 1000 meters times 1000 meters = 1,000,000 square meters) there could be

1,000,000 square meters in a square Kilometer     = space for 100 snorveps.
10,000 square meters per snorvep

So the carrying capacity is about 100 snorveps per square kilometer. There could be small socially organized groups of them because they could live fairly close together.

Questions:

Consider that each mature snorvep weights only about 8 pounds. If snorveps weighed 800 pounds each, could they have a society? Would their rather limited mobility and required feeding area make social development difficult?

Notice that there are no seasons on the snorvep's planet. If there were seasons, you would need to figure out what resources they would need to survive the winter (or a hot summer of drought).

Another Question:

What and how much do your aliens need to drink, and are there any adaptations that they need to make in this area?

Assignment: Describe what your aliens eat and draw a food pyramid diagram for them. Calculate the land area required to support each alien.