An ecosystem may be as small as a rotten log, or as large as the planet, but we define an ecosystem as an area with uniform soil, vegetation and organisms. Some of the relation-ships are understood.
Plants harness energy from the sun and provide food and shelter for animals.
In turn, many plants need the help of animals to reproduce. Animals eat seeds and spread them, undigested, to other places. They also spread seeds by picking them up on their feathers and fur. However, there are many relationships that are hidden from our sight and we are only now beginning to understand. There are millions of bacteria, tiny plants and animals in the soil.