If they never developed aggression then they are not eating each other. Animals eat other animals because of the high concentration of nutrients in living things. Eating highly nutritious things allows an organism to develop both physically and mentally.

So they either have an abundant source of nutrients that has not been depleted for their entire evolution, or they are not highly developed, or they have developed aggression.

I agree, but plants are nasty too, just in slow motion.

For example some ficus grow over other trees, and later the roots cover the old tree until it dies. They don't eat the other tree, just "reuse" the wood to have an initial high place to get light. I coudn't find a nice link about this, but here are a few photos https://www.flickr.com/photos/rodolfocol/15129590163/in/phot... https://www.alamy.es/brasil-el-pantanal-parasito-higuera-fic...

Also, the eternal war between grass and forest comes to mind, the concept of fast, regenerative and self-destructive vs longterm investment killing the looping upstarts below.

Include in that the fire-economy of some forest and savannahs + the animals marshalled by these ecosystems and "peaceful" nature stops looking peaceful