well on a basic level, farming, agriculture and animal husbandry. nature is very finely tuned, and every organism does do/privides a funtion.
Everything is connected.
What breaks down animal poo? insects, slugs eat dog poo, dog poo is a hazard, over in the UK now, they have a huge problem with dog poo, disposal.
you cannot compost it, you cannot put it on food crops.
So, herbivore eats the foliage, and poops, insects eat/break down poop, poop, feeds the ground/land.
Carnivores, eat the herbivore.
If carnivores are not controlled, or if they are eliminated, it upsets the whole ecological balance.
Hen's clean up parasite form pastures, rotation of crops, planting and growing certain crops / plants, sheep clean up worms from cows/horses and vice-versa.
If you graze only horses on the land, it become's 'sour' full of 'roughs and pastures', the horses won't eat the 'roughs' as they are loaded with parasites from their poop.
hence the need for mixed/rotational grazing and good land management/husbandry.
Even hedgerow plants serve a purpose.
Vegetables, companion planting to control pests, improve soil.