brown rat

Humans have explored the entire face of the planet, but we haven't done so alone. Animals and plants came along for the ride, some as passengers and other as stowaways. Today, these hitchhikers pose one of the greatest threats to the planet's biodiversity, by ousting and outcompeting local species. Islands are particularly vulnerable to invaders. Cut off from the mainland, island-dwellers often evolve in the absence of predators and competitors, and are prone to developing traits that make them easy pickings for invaders, like docile natures or flightlessness. Two years ago, I wrote about…