I am in the Philippines on a post-grad school vacation. I have been intensely documenting biodiversity loss for the last two years, and wanted to let it all go. But the biologist in me can’t take a break!
My first night in Manila, I met up with a friend at the Greenbelt, one of Manila’s many, gigantic malls. We took a stroll through an outdoor garden area, which was overrun with both stray cats and cane toads. In our 200 meter stroll we saw at least 2 dozen cats eating dry food (regularly set out for them by animal loving humans), and roughly 75 cane toads, eating the cats’ scraps.
I love cats, but free range cats are possibly the worst invasive species on the planet, as destructive even as humans. We’ve all seen cats deliver a near dead bird or mouse to curry their Human’s favour. So it’s no surprise that cats kill native species not just to survive, but additionally for sport. Cats have contributed to 1/3 of modern bird, reptile, and mammal extinctions recorded by the IUCN. In the U.S. cats are estimated to kill as many as 3.7 billion birds per year. That’s billions, not millions! To put it in perspective, that’s worse than wind turbines, cars, pesticides and windows– some of the most infamous anthropogenic sources of bird mortality.
Cane toads are true toads, native to South and Central America but introduced to many tropical islands. They were originally introduced to many islands because of their voracious appetites, as a method of pest control in agriculture. Cane toads were introduced to the Philippines in the 1930’s to control sugar cane pests. By that time the toads had already been lauded for successfully reducing crop damage to sugar cane in Puerto Rico, where it reduced populations of white-grub.
The downside is they can grow much larger than native species — in places of low population density they can weigh in excess of 5 pounds. That’s bigger than a lot of newborn babies. So not only does it kill native species by eating them, it kills them by outcompeting them for food and other resources. Like many successful invasives, they tolerate, and in some cases prefer, human disturbed environments (like the Greenbelt). They are also much moved tolerant of drought than other species.
Cane toads are perhaps most famous for their astounding impacts on the reptiles and amphibians in Australia, but they are listed as an invasive species in over 20 countries. They are prolific breeders, and they have toxin producing glands, making them unpalatable to poisonous to most animals. Even the tadpoles, normally a delicious contribution to an aquatic ecosystem, are toxic.
These invasive species impact can be devastating in island environments where species are more likely to be endemic (unique to that area), and thus, more susceptible to extinction.