World
The world is generated from a single number, its seed. It is 12 screens wide in total, and no two parts are alike: some regions are fertile and wet, others poor and dry. Nobody places the creatures: they spread, settle or leave on their own.
Where life is now
Green is fertile ground, dark is poor ground, blue is water. Each dot is one living creature: pale yellow lives on land plants, light blue on water plants, red mostly on meat.
Weather, place by place
There is no single weather for the whole world. Clouds form over wet regions, drift with the wind and rain where they are thick. Rain soaks the ground, plants grow with the water in the soil, lightning can start a fire on dry land, and in winter the cold regions go under snow.
Water in the soil
Clouds
Both maps are the state of the world at the moment this page was written. The weather is part of the simulation and follows from the seed: nobody chooses it.