Final answer:
An invasive species becomes a problem when it outcompetes local organisms after being introduced to a new place by humans. This disrupts the ecological balance and threatens other species.
Step-by-step explanation:
An invasive species becomes a problem when humans bring an exotic species to a new place, and it outcompetes local organisms. This can happen when the exotic species has characteristics that make it especially successful in the new ecosystem, leading to a dramatic increase in population and a disruption of the ecological balance. The invasive species then threatens other species through competition for resources, predation, or disease.