The ecosystem is indeed huge, the one who are creating in the ecosystem are animals and plants both are the one who creates the ecosystem.
The interactions that occur between organisms in an ecosystem: Predation, parasitism and herbivory.
Predation - Predating another animal for a prey
E.g : Lions And Antelopes
Paratism - Some small things that lives with the host, it can harm the host or harm the parasite.
E.g: dogs and lice or bacteria and humans
Herbivory - animals that eat plants
e.g: Sheep And the grass
Glad I can Help!