Petri 1.0.1 is distributed with two sample dishes, "Sample Dish One" and "Sample Dish Two". This ReadMe file describes these two dishes, and discusses some aspects of creating successful survival strategies.
Sample Dish One
This dish has two life forms, grass and bugs. Grass and bugs are both Easy Species. The dish is at cycle 1400 when you open it, and the grass and bugs are scattered about.
Grass is a general purpose plant that's easy to make and easy to grow. As a plant it does not move around by itself, and lives off of visible light. Grass has a moderate life span and reproduces well. With lots of light and no predators it will grow to fill the dish.
Bugs are a kind of animal. They will sometimes move on their own, if they have enough energy, and will move to eat some grass. Bugs lose energy when moving, so they need to eat to get their strength back. Bugs can also gain a little energy by absorbing ultraviolet light.
In this dish the bugs must eat grass to get enough energy to reproduce or to move. Often they will over-eat an area, consuming all the grass, and leaving them without a good source of energy. The ultraviolet light can keep them alive until the grass grows back. When grass grows close enough to these "dormant" bugs, they will eat it and start moving and reproducing again. But if the grass does not reach the dormant bugs, they will eventually die.
Sample Dish Two
This dish has two life forms, grass and big dogs, which are both Easy Species. The dish is at cycle 800 when you open it, and grass is everywhere except for a little patch of big dogs near the center. This is a wrap-around dish.
This grass is the same as the grass in Sample Dish One.
Big dogs are animals, and they get all of their energy from eating grass (OK, so this is not like real life). Big dogs move around a lot, and they eat lots of grass. These behaviors help them to spread out, but have the effect of making it more difficult to find a mate. They reproduce easily (using low energy) in order to make up for the fact that opportunities to mate are rare. Big dogs have a more difficult time surviving as a species, and so their population is generally low.
Species Survival Strategies
As you create new species, you decide how life forms will interact with their environment (absorb light energy, move around), interact with life forms of other species (eat, be eaten), and interact with life forms of their own species (reproduction). Creating new species will cause you to think about how the life forms are to survive. What will keep them going? What will give them an advantage in the life-and-death struggle in the Petri dish?
Plant Species Survival Strategies
Plant species survival strategies can be very simple. Plants normally don't move and they don't eat other life forms. In a dish that contains only plant species, the empty space in the dish is the only thing that they compete for. All species take up more space as they reproduce, yet they will only give up their space as life forms get old and die. When this happens, it allows a competing species to try to grow into that empty location.
Plant species that reproduce quickly and live a long time give up their space very slowly, making it hard for other species to get more room. Dishes that contain these species tend to fill up quickly and change very slowly. If you create several species that absorb different kinds of light (visible / infrared / ultraviolet) and put them into the same dish, you can control the growth rate of each species by adjusting the amount of each kind of light in the dish.
In dishes that contain both plants and animals, other factors come into play. Since the plants don't move and they don't eat other life forms, they can devote all of their energy to reproduction-this can give them an advantage over the animals. But these same behaviors cause the plants to be found in groups by animals that can eat them, and since the plants don't run away, they are easily eaten.
Animal Species Survival Strategies
Animal species survival strategies tend to be more complicated than plant species survival strategies because animals generally move around. This behavior makes animals spread out much faster than plants, but gives them one big drawback-reproduction is more difficult when they wander off in all directions. The key to creating successful animal species is balanced behavior. How does the species survive while it wanders around?
Animal limitations-it is important to note that Petri life forms (in this version of the program) are limited in how they sense other life forms around them. Life forms don't have any long distance sensors-they can't detect other life forms unless they actually bump into them. This means two life forms can't see, hear, or smell each other across an empty space; they can't choose to move toward each other or away from one another. Eating and reproduction occur only when two life forms make contact accidentally.
Animals can move for one of two reasons. The "moving" trait controls random movement, while the "eating" trait controls move-to-eat movement. Random moving occurs only when the life form has enough energy to move and only as often as you have specified. The time between moves and the direction of movement are both random. Move-to-eat behavior occurs only when the life form eats, and the direction of movement is random to any adjacent space with food in it.
Random movement consumes energy, but can put the life form in a better position to find food or a mate. But since random movement is energy consuming, the life form may not have enough energy afterwards to "kill its food" or to reproduce. You define what those energy requirements are.
Move-to-eat movement is energy producing, since eating provides energy to the life form. With more energy after moving and eating, the life form may be able to reproduce. Depending on the "hungry" levels you choose, a life form may eat several times in a row or just once. Sometimes a hungry life form can burrow far into a plant-filled area by eating over and over again. These life forms can easily get separated from others of their species, and die of old age, alone, surrounded only by food.
Reproductive behavior can vary greatly for animal species. When two life forms produce a baby, the baby is given an initial level of energy that is not more than the parents put into it-the baby does not get free energy. Of course there are trades to be made between high-energy and low-energy babies.
High-energy babies have a greater chance of surviving in the environment because they can survive long enough to perhaps come into contact with food before they die. But high-energy babies can't be made very often because the parents have to store up enough energy to produce them.
Low-energy babies have a greater need for immediate feeding in order to survive. If food is not close by they will die. But low-energy babies can be made more frequently because the parents don't have to store up as much energy for them. Low-energy babies can be made in greater numbers but will survive less often than high-energy babies.
Survival strategies of species in a Petri dish can be compared to those of real world species. There are some real species that produce very few babies, but do everything possible to guarantee their survival. There are other real species that produce many babies "hoping" that at least a few will survive. Both strategies can work in the right settings.
Potential Learning Opportunities
Petri species are controlled by relatively few genetic traits. Even so, the interactions among different life forms can be quite unexpected. There are some interesting learning opportunities. Consider the following example.
One of the most striking behavioral consequences that can be demonstrated in a Petri dish with just two species is that of over-using the environment. A species that eats all of its food supply does not survive for very long.
There are so many possible combinations for dishes with multiple species that relatively few have been tried to date. Who knows what interesting-and possibly useful-examples may be developed.
I hope you enjoy using Petri and making up your own species and dishes. If you come up with something that's really interesting, let me know-I'd like to be able to share it with others.
