Final answer:
Invasive species unbalance ecosystems by lacking natural controls and overpopulating, leading to competition for resources and threats to native species.
Step-by-step explanation:
Invasive species frequently disrupt ecosystems due to their lack of co-evolution with native species and the absence of natural regulatory mechanisms. These invasive species have the potential to overpopulate and consume local resources, leading to competition for resources, predation, and disease that threaten the native species. For example, the Eurasian star thistle has invaded and rendered useless some prairies in the western states.