Human Impact and Conservation

Invasive species, organisms introduced outside their native range where they establish and spread aggressively, often disrupt ecosystems because native species have evolved no effective defenses against a predator, competitor, or disease to which they were never previously exposed. The introduction of the Nile perch into Lake Victoria in the 1950s and 1960s, intended to boost commercial fishing, is widely cited as one of the most dramatic examples of this dynamic, since the large predatory fish is believed to have driven numerous endemic cichlid species to extinction or severe decline within a few decades. On islands, which typically host species that evolved in the absence of mammalian predators, introduced rats, cats, and other mammals have caused a disproportionate share of global extinctions recorded in recent centuries, a pattern documented across island groups from New Zealand to the Galápagos, prompting extensive and often successful invasive-predator eradication programs on smaller islands as a conservation tool.