These exotic species monopolize the ecosystem's resources, and since they have no natural predators to decrease their growth, they are able to increase indefinitely.
Olsen et al.[1] showed that exotic species have caused lake and estuary ecosystems to go through cascade effects due to loss of algae, crayfish, mollusks, fish, amphibians, and birds.
The prey is then able to overexploit its own food resources, until the population numbers decrease in abundance, which can lead to extinction.
Starting before the 17th century and not phased out until 1911 when an international treaty was signed to prevent their further exploitation, sea otters were hunted aggressively for their pelts, which caused a cascade effect through the kelp forest ecosystems along the Pacific Coast of North America.
[6] In conclusion, the loss of sea otters in local areas along the Pacific coast seems to have caused a cascade effect of secondary extinctions, continuing into the present day.