The 1954 introduction of the Nile Perch to Lake Victoria, Africa, was a cascading disaster for the ecosystem.
Common myna bird
The common or Indian myna is native to central and south Asia, but the pet trade has spread the birds across Southeast Asia and the Pacific. They're also found on islands in the Atlantic, in southern Africa and in Australia and New Zealand.
Mynas roost by the thousands, elbowing out native species, damaging crops and creating a health hazard with their droppings. On isolated islands like Saint Helena in the Atlantic, mynas prey on the nests of endangered birds, stealing eggs and eating newly-hatched chicks.
It may seem strange to think of your feline companion as an invasive alien, but domestic cats were one of the first species to be spread around the globe by humans.
Domesticated in the Mediterranean 3,000 years ago, cats were prized for their ability to kill another human hanger-on, the rat. Sailors took cats to sea and to new lands, often abandoning any feral offspring. Native birds and small mammals suddenly found themselves hunted by a new predator.
Cats' impact continues in the modern day. According to the IUCN, cats have contributed to the decline of 76 bird species in New Zealand, six of which are found nowhere else.