What are some of the natural barriers to species movement/migration that isolate them and create habitat islands?

Mountains and Oceans

Explanation:

There are various natural barriers that prevent species from migrating such as Mountains and Oceans. If a species does not have the physical requirements to swim across an ocean or climb over a mountain it completely prevents them from passing such a barrier and moving to another geographical location to establish a new habitat. This ultimately causes them to stay in place and create a habitat island. There are many other natural barriers as well such as valleys, and rivers, waterfalls, and even weather effects such as snow habitats which some animals can't survive in.