For what it is worth, here are some sources of information on predation, ecosystems and the intricate roles that are played by each niche.http://www.eoearth.org/article/Predationhttp://www.globalchange.umich.edu/gl...ecosystem.html
It is often that people speak from the heart and wish for a world of pure compassion and unending life. Those are very admirable goals and reducing suffering for all life is an important part of a good life that we all should strive for. But it is equally important and essential to realize that life is about balance and cycles. Life and death are entwined and necessary to each other. To make important wildlife management decisions based on our desire for a compassionate perfect world without accepting the reality of the world as it is, is counterproductive to our goal of reducing suffering and supporting Mother Earths overall health and wellbeing.
Without predators the herbivores would eat all the plants and then die of starvation and disease. While this is simplified, it makes the point that the concept of no predators maybe appealing, it is not practical in a healthy balanced environment. The Earth seeks balance and part of that balance involves the death and consumption of organisms so that other organisms may live. Predators prey on the sick, weak and infirm. They kill quickly and consume their prey with the purpose of self survival. Without predators, the prey species would suffer from other ailments and issues such as starvation. As an overall species, they would be denied the ability to have only most adapted and strongest carry their traits to the next generation thus producing even better adapted future generations of that species that have an even better chance of a happy, full life in the wild.
This should not be confused with humans who kill the strong, healthy and beautiful for sport and whimsy often only gathering a trophy and sometimes just the choicest bits of flesh. This results in the species having less of some of its best traits in future generations. When humans attempt to control ecosystem balance, we cause horrific changes because we manage not for the good of the whole but for our own selfish purposes. I fully support balanced healthy ecosystems that allow all life to live in harmony with the understanding that natural harmony involves consumption and each new generation having traits that help that species survive in the present conditions.
I'm not sure we should strive so much for a return to the past, but it is essential and necessary that we return to some kind of balance that is not dependent on humans to maintain or oversee it. Because of generations of mans arrogant and ignorant resource management decisions, we have severely altered our environments. We now produce food in factory farm conditions that are beyond cruel and inhumane. We alter plants at a genetic level to suit our whim for round red tomatoes that will sit on the shelf of our grocery for weeks sometimes months instead of relishing the goodness of a fresh tomato from the garden that is only a few days off the vine. A list of the many ways we, as a species, rape and destroy the Earth is long and shameful. It would take a lifetime to record every indiscretion. It is these human made atrocities that we should oppose, not the predators who make up an important thread in the fabric of life on Earth.
I would feel more optimistic about a bright future for man if he spent less time proving that he can outwit Nature and more time tasting her sweetness and respecting her seniority. ~Elwyn Brooks White, Essays of E.B. White, 1977