A good god could, if it wanted to, have designed all life so that it is directly sustained by manna from heaven, with no need for consumption of biological matter. But almost every form of life must by its very nature capture, kill and eat other living beings in order to survive. Without this murderous torment, life is impossible. If not by direct consumption, then, organisms must still acquire biological matter at the expense of others: the competition for food is also a case of living beings being required to outdo each other merely to survive. There is no way to live life along a principal of do no harm.
If life was created, and not simply the result of undirected unconscious evolution, this is surely the worst possible way to have created life. A god could not have created a more vicious cycle if it tried: tying the very existence of life with the necessary killing of other life is the work of an evil genius, not of an all-powerful and all-loving god. Either no god ever instigated life or guided it, or, such a god is monstrously evil.
Evolution itself is a result of the endless struggle between predator and prey; but those words normally refer to the animal kingdom. It is worth remembering that it extends to - and started with - the world of plants. Not only that, but the whole system by which the survivors get to produce the next generation means that it is normally the more violent, the more vicious, that has an advantage.
“Capsaicin, glucosinolates and hundreds of thousands of other chemical compounds produced by plants appear to be the products of millions of years of evolution in which plants have evolved deterrents and toxins against their natural enemies. [...] Every novel defence by a plant gives an advantage to any natural enemy able to evolve a means of overcoming that defence. Natural enemies with this advantage spread, and thus the enemy population evolves along with the plant population. This process is called coevolution and has been compared to an arms-race. [...] The evolutionary arms-race between plants and herbivores is a ceaseless one. Genetic variation is the raw material of evolution, and within populations it plays an important role in the evolution of defence.”
"Biodiversity and Ecosystems" by Silverton, Wood, Dodd & Ridge (2008)1
The desperate, deadly struggle for existence was agonized over by the father of evolutionary theory, Charles Darwin.
“I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us. There seems too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly create the Ichneumonidae [wasps] with the express intention of their [larva] feeding within the living bodies of Caterpillars, or that a cat should play with mice.”
Charles Darwin (1860)2
He's not the only one, the philosopher William James, normally so calm and considered, equals Darwin's revulsion:
“Life contains moments as bad as any of those which insane melancholy is filled with, moments in which radical evil gets its innings and takes its solid turn. The lunatic's visions of horror are all drawn from the material of daily fact.”
Talking of those who suffer from depression and melancholy at the real world, William James continues to the point of madness:
“Forms of horror [...] fill the world about us to-day. Here on our very hearths and in our gardens the infernal cat plays with the panting mouse, or holds the hot bird fluttering in her jaws. Crocodiles and rattlesnakes and pythons are at this moment vessels of life as real as we are; their loathsome existence fills every minute of every day that drags its length along; and whenever they or other wild beasts clutch their living prey, the deadly horror which an agitated melancholiac feels is the literally right reaction on the situation.”
Many modern atheists quite rightly use the violence of the food chain to cast doubt on the idea that there can be a god.
“Failure and pain is the norm for life on this planet, predation and extinction the rule. [...] No Hollywood horror film could ever begin to approach the grisly reality of a single minute's activity in the animal kingdom. Every moment of every day, it is business as usual for animals to be eaten alive or even to have their internal organs devoured from within by parasites. [...]
In Africa I saw two lion cubs gnawing on a zebra the older lions of the pride had taken down. Their victim was still alive, even as they worked to tear open its abdomen to devour the warm guts. It was difficult to watch an animal experience such misery. I will never forget the blood-soaked faces and ghoulish excitement in the lion cubs' eyes. But we cannot blame the parasitic wasp or the lion cub for such horrifying behavior. They are merely doing what nature demands of them. Or, as believers might say, they are merely doing what the god who created them wanted them to do. The latter explanation is a bit more difficult to understand, in my opinion.
As the plant world strangles, poisons, smothers and drowns its competitors in shadow and scarcity, there are some tiny and primitive forms of single-cell life that survive in the oceans by passively encountering biological chemicals and (maybe) photosynthesizing light. These simple lifeforms are a Buddhist ideal: They harm no other creatures and feed on nothing living. In a perfect world, all life would have evolved to survive in such a way - through human ingenuity, we can produce energy from non-biological sources. It is possible, but, life would need to have started out radically different.
“We could base life on photosynthesis and chemosynthesis in order to avoid this predator-prey madness that stains our world with so much blood. Had a human with a minimal sense of decency created this world, we might not have all these mosquitoes that spread misery and death in developing nations by delivering viruses into the bloodstream of millions of people-including children. Then again, one could just leave lethal viruses out of the creation recipe.”
Some others, according to the Buddhist author Ken Jones, have come to terms with the violence of nature.
“Ecological 'violence' can equally be seen as ecological 'harmony' and balance. One animal supports the life of another by becoming its prey. 'Violence' harmoniously sustains the life-affirming food chain. Humankind, [...] was part of this harmonious balance of violence-and-peacefulness. [...] Taizan Maezumi, a contemporary Zen Master has observed that if we think of the Buddhist First Precept 'on a common sense level of "Do not kill" or "Do not take any form of life", how could we survive? [...] Survival of life itself depends on killing other forms of life. [...] 'Violence' and 'harmony' [...]. When each disappears, what is there then?”