Question 1.Listen to part of a lecture in an environmental science class. Professor: We tend to think of invasive species as obvious troublemakers, but the damage is often indirect. Take the small Asian mussel that spread through several North American rivers. By itself, one mussel filters only a little water. The problem is numbers. They reproduce so quickly that they coat intake pipes, clog water systems, and crowd out native shellfish that other animals depend on for food. So the lesson isn't about a single organism; it's about how a fast-reproducing species reshapes an entire system. Why does the professor describe the Asian mussel?