Yde girl lived in the Netherlands where there were many forests.  The Celts hunted animals in the forests, fished in the streams, and collected fruits, nuts and berries to eat.  The sun provided light for photosynthesis by the plants.  The trees took in carbon dioxide and gave off oxygen that was used by the animals and humans.

 

When the branches and leaves decayed and fell onto the ground, the rotting vegetable matter was broken down by bacteria, which then provided nutrients for the soil.  The plants would then use those nutrients to grow.

 

Animals’ waste provided further nutrients for the soil, bacteria and some of the insects such as flies.  Birds would eat the insects, and their droppings would provide food for some insects and nutrients for the soil.

 

Primary producers such as the rabbits would eat grass and other vegetable matter.  The secondary consumer such as the fox would eat the rabbit and when the fox died, insects and bacteria would consume its remains.

 

If civilization invaded this ecosystem, with factories and farming, buildings and roads, the forest ecosystem would be greatly disturbed.  The number of animals would be reduced because they would lose areas of land where they could live peacefully and would also lose a source of food.

 

The pollution caused by the invasion of the humans with their technology and machines could result in high levels of gases poisonous to the insects and animals.  The rivers and streams in the forest could also become polluted with industrial waste, killing the fish, and reducing a food source for other animals.

 

If a new species of animal was introduced to this ecosystem, it would consume food that was currently being used by the existing animals, and deprive them of an adequate source of nutrition.  The new animal may also introduce diseases that would affect the local population of animals, killing them and disrupting the normal food chain.