Could a Planet's Ecosystem be run by a small variety of animals?

• In my world, there's an era when only some 20 visible (big enough to see with the naked eye; all other animal life forms are microscopic) animal types lived on the planet. Mammals such as wolves, livestock animals, rodents, small wild cats, as well as a few different types of fish, bird, insect, reptile, and arachnid species.
• Most of the animal types link with each other in a food web and with the ecosystems on the planet.
• Some of the creatures prefer certain climates over others.
• There isn't that much variety in visible animal types (environment or mutational adaptations).

Could such an era be somewhat scientifically possible?

The weather and biome conditions resemble those of Earth.

posted over 6 years ago

BlueTangsRock‭

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