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From rabbiting to killer shrimps: IAS (Part II) in detail

by Dave Armstrong 26 Feb 2013
From rabbiting to killer shrimps: IAS (Part II) in detail

The cuteness of the Easter bunny, Oryctolagus cuniculus is undisputable, but the terrible damage done to sheep pasture, young crops and the horrific desertification are undeniable - Rabbit Image; Credit: © Shutterstock

When the rabbit was brought from Spain to northern Europe, then the British took it to Australia and others dispersed it as a food animal, the inevitable happened. It is a classic. Like the feral cat, the grey squirrel and the brown rat, it is a square mammal in a round burrow. The modern ecologist calls them IAS, but European scientists have started counting the cost of all of their aliens and invaders.

Many plants, too, are invasive, alien, and over here, when they should be over there ! They include rhododendron, water hyacinth, giant hogweed and ice plant, but to complete the animal species that Europe and many other countries most hate, in addition to the crayfish (two) and the Spanish slug we reported on yesterday, they are:

Rabbit, Oryctolagus cuniculus

Raccoon-dog, Nyctereutes procyonoides

Canada goose, Branta canadensis

Common slider, Pseudoemys spp.

Tiger mosquito, Aedes albopictus

Killer shrimp, Dikerogammarus villosus

and the yellow-legged hornet, Vespa velitina.

There are several more such as grey squirrel, but here's the European problem list.

The rabbit is a rapid-breeding leporid, very like the American cottontail (the cottontail has 16 species, all in the Sylvilagus genus), eating anything herbaceous in its native mattoral. Unfortunately, both desert and planted forest suit it down to the ground. The effects it has are complex for the ecologies of its neighbours.

Whileits predators obviously benefit, the habitat degradation is severe, such that islands are rapidly and completely demolished as far as past sea bird colonies or future ecosystem building are concerned. Small animals' habitats are very sensitive to rabbit introduction. The very predators that benefit from rabbit introduction begin predating more on native prey when their population builds up on the back of the rabbit population. With a forced or natural decrease in rabbits, the native prey and the predators themselves often disappear!

Strangely, in Spain and Portugal, the troubled rabbit is now being conserved in order to encourage the recovery of the critically-endangered Iberian, Lynx pardinus.

The yellow-legged hornet is quite similar to the European hornet. It predates on other wasps and bees, along with other insects. Pollination may therefore be severely affected wherever this invader is successful. Several thousand individuals make up each colony, decimating the natives. In the few years it has been present in France, it has been surprisingly successful, though impact can be limited on apiaries by restricting the narrow entrance to the hives. Poisoning and then nest removal is the only recommended removal method, but unfortunately, French and other authorities have been using traps that kill a wide range of insects.

The killer shrimp kills because the large mandibles on this small crustacean are able to nibble at many different organisms from algae to damselflies and snails, including their own relatives, Gammarus spp. Even fish fry and eggs are eaten. Its deadly mouth-parts kill competition off literally, without them being eaten. The result is less leaf decomposition as gammarids eat a lot of leaves.

Whole ecosystems are quickly altered as the habitat changes. Fisheries and even recreational uses of freshwater are affected. Fish catches are affected because trout and perch eat the killer shrimp, while trout and the related salmon genus are possibly infected by an acanthocephalan parasite it carries. With the zebra mussel, well-known to watermen worldwide, this shrimp provides one of our best examples of how two IAS can cause outright chaos in worldwide waterways. Working together, the shrimp benefits from the presence of the mussel's byssus threads and their accumulated detritus, while the mussel also grows much better when the shrimp is present.

Aedes albopictus is just another mosquito, you would think! However, the eggs and larvae of this SE Asian require very little water compared to most mosquitoes. Tin cans or tyres, for example. 20 pathogenic organisms can infect you from this biter, plus the transmission of many zoonoses from other animals such as dog heartworm. Italy has a large tiger mosquito population, which means their daytime biting activity and these many diseases are quite likely to affect at least one European country While the Aedes egypti mosquito feeds mainly on humans, spreading dengue fever and yellow fever, this species will take blood from vertebrates generally- hence its success and its competing-out of these other mosquitoes. Some scientists regard this as a good thing, with the dangers of malaria in many countries. Perhaps the strategy of encouraging the tiger, Aedes albopictus, will eliminate a lot of malaria mosquitoes.

The raccoon dog raises hackles even more. It's a fox-like Asian omnivore, not directly related to actual raccoons. It can hibernate and reproduces - like a rabbit! Pleasant enough animal within Europe, you would think. In fact, it carries many dog and/or human diseases, being an ancestral type. Rabies in eastern Europe is mainly carried by the species. Mange, trichinella ("worms") and the fox tapeworm in particular threaten even human health. While the fox is often responsible for transmission of disease to humans, the raccoon dog has overtaken it in several countries. Ecologically, the raccoon dog seems able to change the role of its amphibian and bird prey in ecosystems. A successful invader, at least as far west as Germany, it needs to be controlled in order to prevent their expansion of territory. Luckily the Judas dog technique seems able to combat the spread by trapping many of this social animal in several locations.

While many species have endearing characteristics, these animals (and plants) have to be controlled in the same way as Australasians have managed to curtail their loss of precious endemic animals and plants. Indicators of invasion have now been developed that cover a broad grouping. Both effects on human health and human economy have to be added to loss of biodiversity in order to have reliable measures of the impact of IAS. More data is needed, but hopefully we can bite h bullet and avoid sentimentality when our native species are dying out in their hundreds.

(IAS: Part I)

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