Living things all have an effect on each other but they also have effects on the climate and soil. The climate inside an oak forest is milder than outside because the oak trees provide shelter. Fungi and bacteria in the soil are important because they return nutrients to the soil by decomposing dead plant and animal material. The climate can have a profound effect upon the kinds of animals and plants which live in an ecosystem. If you take a nice walk up a mountain there comes a point where it is too cold for broad leaf trees like the oak and you find yourself in coniferous forest.
Fir trees can survive in colder places than oak trees.
Don't be surprised to find that the animals are also affected by the climate. It might be very acid, or neutral, or very acid. So there must be enough water and enough oxygen for plants to grow successfully. Plants also need mineral salts like nitrates, sulphates, and phosphates. Plants remove these nutrients from the soil, and decomposers return them to the soil.