From scientists’ boots and in the bottoms of boats, animals from one part of the world have ended up in places far from their own homes due to human activity. In more than a few cases, these “invasive species” have (through no fault of their own) wreaked havoc on endemic wildlife and fauna. In the Galapagos Islands, pigs and goats’ “relentless grazing” has had dire consequences; the rodents have “brought several species — including the rare Pinzón giant tortoise (Chelonoidisduncanensis) — to the brink of extinction” by eating the eggs and chicks of birds, including the Galapagos petrel (Pterodroma phaeopygia).
Via Project Isabela, some $10.5 million has been used to remove all and 140,000 goats from a number of islands. Project Pinzón is another effort that involves dropping a rain of blue pellets — rat poisoning — from helicopters to rid three islands of rats. The logistics of the plan are complex (conservationists had to make sure that no endangered animals — tortoises, finches — might eat the poison and perish); if it is successful, it will make Ecuador something like a “world leader in the eradication of invasive species,” as Nature comments.
Project Pinzón began in November of 2012; conservationists will be monitoring the islands for two more years before declaring it successful, or not. Constant vigilance is necessary. Nature notes that, in 2009, “some malcontent set six goats down on Santiago, which by then had been goat-free for around three years”; $32,393 — more than $5,000 per animal — was needed to remove them.
There are certainly other, non-lethal methods to remove invasive species. New Zealand has sought to reduce its possum population by building fences. It pays to take preventive measures such as supervising ballast water discharge (most of the 185 invasive species in the Great Lakes were introduced from such). We can encourage the use of “compassionate conservativion” to manage invasive species while minimizing any distress and pain for them and keep in mind that, in some cases (invasive boars in Brazil), non-native animals can be a benefit to the ecosystem they find themselves in.
Here are five other examples of invasive species who have had a detrimental effect on the places to which humans have introduced them.
1. The African Clawed Frog Spreads a Lethal Disease to Other Frogs
Until the early 1970s, African clawed frogs (Xenopus laevis) were used in pregnancy tests: the female frogs ovulate when exposed to a pregnant woman’s urine. Other pregnancy tests have since been developed and many hospitals released the Xenopus frogs into the wild, with dire results.
A lethal fungus disease, chytridiomycosis, appeared in the 1960s and wiped out hundreds of frog species. A new PLoS One study has found that, while Xenopus frogs are carriers of the fungus that causes the disease, they do not themselves catch it, so they have ample opportunity to spread the fungus to other frogs. Other species of frogs have perished from the fungal disease, which results in their skin becoming forty times as thick.
African clawed frogs are still widely used for research purposes. Between 1998 and 2004, more than 71,500 were exported from Africa as lab animals. The World Organization for Animal Health in Paris says all frogs should be tested for the fungus before being exported and infected animals treated or quarantined to help prevent spread — but compliance (certainly in the U.S.) is uneven.
2. Asian Ladybugs are Wiping Out Ladybugs Native to Europe
The harlequin or Asian ladybug is native to Central Asia. It has been imported to Europe and North America to control aphids and is now threatening the existence of native species, including the seven-spot ladybugs (Coccinella septempunctata) by overcompeting for food or eating other ladybugs.
Entomologists have found a specific reason for the harlequin’s survival: its blood or haemolymph contains a microsporidian parasite. The harlequin’s eggs and larvae contain this parasite in a “dormant and harmless state” but it can be fatal for other ladybugs. As ladybugs often eat other ladybugs’ eggs and larvae, the ones who consume those of the harlequin are infected with the parasite.
Other scientists point out that the harlequin’s success may be due to its being more resistant to a fungal disease that attacks ladybugs native to Europe.
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