Answer:
There are only two real sources of energy on the earth. One comes from geothermal from the creation of the earth and the other comes from the sun. You can say wind and nuclear or water, but water's movement is related to the tectonic activity and shaping of the earth and its spin, wind comes from unequal heating of the earth by the sun and nuclear energy comes from isotopes that were formed by a star. So producers are able to harness one of those two energy sources, the sun. Trees and plants are so common because they are using free energy, they have discovered a way to get something for nothing essentially. Predators can use the nutrients they make to supply their own energy but in the end everything boils down to the producers ability to make energy from the sun.
