Why are animals important in the ecosystem?

Here are just a few of the many reasons that modern ecosystems depend on animals:

Animals help to keep plant species from overcrowding each other by eating them. Many animals help to spread the seeds of plants, either by carrying them on their fur by accident, or by swallowing seeds they can't digest when they eat fruit and later depositing the seeds elsewhere in their excrement. Specific animals, especially bees, pollinate most modern species of flowering plants, allowing them to create seeds and reproduce. Animals help to recycle nutrients in the ecosystem so that plants can use them again (i.e., earthworms eat dead plant material, making its nutrients bioavailable for plants; all animals release carbon dioxide, which allows plants to make food; etc.). Additionally, some animals specifically alter the ecosystem allowing for certain plants to grow (i.e., beaver dams create wetlands, elephants clear trees allowing for more grasses and shrubs to grow in the savanna, etc).