When all the food chains in an ecosystem are joined up together, they form a food web. Here is an example of a food web:
Although it looks complex, it is just several food chains joined together. Here are some of the food chains in this food web:
grass → insect → vole → hawk
grass → insect → frog → fox
grass → insect → vole → fox
This leads to some interesting effects if the population of a particular organism in the food web decreases. Some animals can just eat more of another organism if food is in short supply, while others may starve and die. This in turn can affect the populations of other organisms in the food web.