Killing intelligent species is a crime
In our world, humans are intelligent and animals are not. So killing humans is a crime while killing and eating animals is not.
Unlawful killing will cause war
In your supposed society, all creatures are intelligent (living creatures with human-like intelligence). Killing any intelligent person (of any species or race) will be a crime. Big animals will not be able to eat small animals as they will protest and force the authorities to pass laws for their protection otherwise there will be a war using weapons.
Distribution of resources
All species are intelligent so they will demand fair distribution of resources. Unfair distribution of resources will lead to chaos, revolutions, wars as happened in human societies in colonial era.
Population will adjust to resources
If there is no colonialism, slavery, oppression and all species have equal rights on all the resources, then population of all the species will adjust to the available resources.