It is important to understand some fundamental differences between animals and plants. These differences govern the forms and life styles of both plants and animals, in water and on land. There are fundamental differences in how they capture energy, why and how they move, and how their bodies are shaped and grow. If there is not enough light or water where they are rooted, they die. However , they make lots of seeds so that a few will find places where they can prosper.
Primary producers can use other energy sources than light.
The primary producers around our deep ocean volcanic vents use heat and sulphur dioxide that are in the water. Scientists wonder if there is life under the frozen oceans on Europa or other distant moons. For animals, the problem of staying alive is more difficult. All animals are dependent on the food created by plants. Some animals eat plants, and some eat other animals.