This they have been for millions of years, and will forever remain so, or starve to death. The lion arid the lamb peacefully sleeping together might be a great philosophy for the lamb, but a very sick and suicidal philosophy for the lion. Should the lion be foolish enough to embrace it, he and his species would soon starve to death and become extinct. Most species of fish, birds, insects, reptiles and mammals are predatory. In short, they hunt and kill other species of life and consume them as their daily food.
Fish eat tadpoles, shrimp, minnows, and in general, the larger fish eat the smaller fish.
The plankton, which derives its food from the minerals of the ocean water, is the great exception, but then there has to be a starting point. From there on out it is mostly fish eat fish, and on up the ladder. Birds eat insects, worms and other live creatures different from themselves. However, hawks, eagles, falcons also hunt and kill other birds and consume them as food. Others form Prey.