biology zoology blog benno meyer rochow invasive species

Wanted and Unwanted Immigrants

And I don’t mean humans

A few years ago the “killer bee invasion” was feared in the USA; now it’s the “murder hornet”. I wanted to use this example for a talk I had planned to give at a conference about “invaders”, animals that arrive from somewhere and stay (or die). I also wanted to talk about the confusion and uncertainties that exist with regard to terms like autochthonous, indigenous, endemic, native, etc. It really isn’t easy to say with certainty if a species has evolved in one location or has got there from another place from where it may ultimately have disappeared and, if so, whether the colonization was the result of an accidental transport by rafting, aided by the wind or ‘hitchhiking’ on birds. I got interested in this, because on Hachijojima, a volcanic Pacific island 300 km south of Tokyo, inhabited by people who until ca. 70 years ago had their own language, I noticed a multitude of species that shouldn’t have been there: rats, ferrets, cats, etc.

But what about the non-mammalian vertebrates: two snake species; one toad and 3 species of frogs (American bullfrogs, introduced after the 2nd World War, are probably now no longer residents on the island). How did they get there? Snakes were presumably deliberately introduced to kill mice. Attempts to eradicate the Japanese toad exist, but I think it’s already too well established. Then there is the firebelly newt, a harmless species that seems to have arrived in the early 1970s and (as we were able to show by molecular studies) from one place of origin in Japan with all individuals on the island related to each other. Maybe children (or a teacher) took some eggs or a few adults from Shikoku as pets to Hachijojima and released them. The newts are now everywhere, but nobody minds as they’re harmless and quite cute.

It’s a different matter with millipedes, thousands, nay millions of them! Most people hate them and say they stink; others see them as a nuisance as their crushed bodies make the road slippery and only a few gardeners tolerate (or even like them) as they do not attack healthy plants or fruit, but shredder dead plant material and help recycling it. They are known to have come from Taiwan in 2002.  Also, from Taiwan are the now widely distributed whip scorpions. And another immigrant from Taiwan was the terrestrial leech that I readily found when looking for it (it had never before been seen by locals or scientists who had been searching for it: probably because of its similarity to earthworms it was always overlooked). Unsurprisingly, two species of nematode worms that had hitched a ride as parasites in the millipedes were also recorded for the first time. A species of earthworm known from India turned out a new find and for the first time for Japan a Canadian freshwater limpet was recorded from Hachijojima by me. The freshwater crab Geothelphusa dehaani (a non-native) must have been introduced, because people eat it; fireflies, too, were deliberately introduced, but to attract tourists to the island. Slimy and alien earthworm-eating planarian flatworms, however, (I collected 4 species) would be less attractive.

But how come all these diverse alien creatures (surprisingly many from Taiwan) can survive and thrive on Hachijojima? The main reasons are:  Hachijojima even in winter does not experience frost; there is a lack of predators and Hachijojima has had a number of volcanic eruptions, some thousands of years ago, the last one (involving only the northern region of the island) 330 years ago. Such upheavals lead to species extinctions and create ‘spaces’ for new introductions. Finally, the surprising variety of habitats on the island meant that there are niches for a large number of alien arrivals. And they, in turn, allowed me to find “my niche” as a keen observer of Nature and her inhabitants while on this wonderful island!

© Dr V.B. Meyer-Rochow and, 2020.
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