Barrblues asks, "What gives humans the right/justification to do what we do to life forms other than human?"

If you are Jewish or Christian go to Genesis 1:26,
"And God said, Let us make men in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth the earth."

If you are not then I would say that as an omnivore man has always been a preditor and as such a member of the food chain, and of nature itself. As modern man and the only animals with anything approaching the ability to reason we have accepted a responsibility for the management of earth. Now we can argue details all day with answers varying. Some such as PETA will argue nature will take care of itself and we humans just need to stay out of the way. Whole books are written as to why that is morally bankrupt and unworkable. Others seek the industrializaton for man at any cost which carries its own inbalances. We as sportsmen fall in the middle.

Plenty of case studies shows that the animals need to be managed as a species, not individually, balancing populations, food and habitat available and human demands. Game cannot be stockpiled without starvation and disease occurring unless individuals are removed by preditors; animal and human. That may occur by use of rat traps, poison for grackles, starlings and sparrows in some areas or a combination of cougars, coyotes, wild dogs and man in the case of ungulates. While few modern men wish to remove all predators I think most will want them controlled as well.

Given time and research resources I could write books but will wrap it up hear. Religiously the Bible gives us that right. Otherwise we become self appointing as the top of the animal kingdom hierarchy and the only animal with the ability to reason. To argue otherwise is in my opinion like OETA, HSUS and others...morally bankrupt.