Populations are a dynamic element of nature. They are dependent on food, space and predation to change. When a large population has enough food then it may continue growing. As the population grows for one group of animals so it grows for another group of animals. For example if there are a lot of mice then the owl population may increase as there is a lot of food for the owls. Conversly though if the population of mice decreases then the Owls will suffer as they no longer have enough food to sustain themselves.
Species are divided into two main groups, producers and consumers. Producers are living organisms such as grass, sea weed and other photo sensitive organisms who can photosynthesise their energy. The populations of producers are very high most of the time because they are far more efficient at getting energy than larger animals such as cows and wolves for example.
Consumers are divided into several sub sections, for example a cow is a primary consumer whilst a wolf is a secondary or tertiary consumer. They are dependent on other animals and plants for their survival as they are unable to use the sun to produce their food in the same method.
If we take the population of grass in the savannah to be around 10,000 KJ then as we go up the food chain we find that wilde beast are only 1000 KJ whilst cheetah are around 100 KJ. This means that a lot of energy is lost as we go up the food chain which explains why we may find one million blades of grass, five thousand wilde Beeste and four lions within a designated area.