Evaluating the effects of the invasive cane toad (Rhinella marina) on island biodiversity, focusing on the Philippines

The negative ecological impacts of invasive species are well documented, although their effects are often more pronounced on islands than on the mainland. This is because many island species exhibit high degrees of endemism, have small geographic distributions, are rare, and exhibit low genetic diversity, which reduces their ability to respond to new emerging threats. One of the world's most notorious invasive species is the cane toad (Rhinella marina), which is a voracious predator that is native to the neo-tropics but was intentionally introduced in the early 20th century to many warm regions and islands to control crop pests. Cane toads produce two kinds of toxins in neck glands that are often lethal to non-adapted predators in the invasive range. Although well-studied in Australia, their ecological impacts on many islands have received much less attention. Australia is the sixth largest country on Earth, so the effects of cane toads on small island nations may differ considerably from there. Here, we discuss the potential ecological impacts of cane toads in the Philippines and on other island nations. Cane toads were introduced onto the largest Philippine island, Luzon, in 1930 and have since spread over all but a few of the 7641 islands that make up the country. We speculate that, unlike most biological invasions with predators or herbivores where the ecological effects are strictly 'top-down', cane toads, by virtue of their biology and ecology, may have even more serious effects on island fauna because they exhibit both 'top-down' and 'bottom-up' effects.