Has an invasive animal ever been removed from it's new eco-niche, once established?

I was reading about the plight of the red squirrel in the UK the other day, that has been pushed out of it’s eco-niche in Britain by our more aggressive gray tree rats, and then thought about our own problems with Chinese snakeheads in Maryland, and Australia’s experience with the cane toad.

Has there ever been an instance of an invasive animal being effectively removed from it’s new eco-niche, once established?

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My dad recently captured some grey squirrels from a neighbours loft using an ingenious home made squirrel trap. He released said squirrels into a nearby wood.
I pointed out that this was illegal under the Destructive Imported Animals Act 1932. But I said I would not tell on him to the police.

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Interesting question. No, not that I know of.

I’m not an expert on animals, but I can name many examples of invasive plants filling ecological niches in the Netherlands in the last 30 years.
For example, there have been a few escaped aquarium/gardenpond plants that escaped and subsequently became a pest in the local canals. An example is Elodia Canadensis. They’ve tried to control it, quite active, but unsuccesfully. After about 10 to 15 years, it found a balance and now no longer is a pest.
For others the balancing out takes longer, like the tree Prunus Serotina in Dutch forests. It is lest of a pest then it was 10 years ago, but still a problem locally.

From what I remember… There was an article somewhere in UFL-NAPA about how a team led by UF scientists was able to erradicate some (invasive) tree parasite.

Here is the link.

The dept of conservation in NZ has has success on some small islands. They were cleared of pests like possums, rats, rabbits, stoats etc and are now used as sanctuarys for endangered native birds. These are very small areas though.

here is one example http://www.doc.govt.nz/Conservation/Showcase-Areas/Tiritiri-Matangi-Island.asp

There have been a number of successful cases, and the titles from the International Conference
On Eradication of Island Invasives
will give you a good start.

There has been a successful eradication of rats from the outlying islands in Antigua which has enabled the return from the brink of extinction of the Antiguan Racer Snake (the only indigenous species). It also allows for the breeding of birds on these islands.

It is rumored that St. Patrick was successful in getting rid of snakes in Ireland. However, I do not know if they were invasive (brought in by Protestants) or not. :wink:

There have been hundreds of examples I can think of, but to allow for a factual answer Astro you are going to have to define ‘established.

For example the Romans introduced both the rabbit and the edible Dormouse to Britain. Both species are recorded as having gone wild during Roman occupation, but they vanished completely within the next 500 years and had to be re-introduced by subsequent invaders. Would you consider that these species had been established, and why or why not?

I’m not sure there’s going to be any factual answer to the question as posed because ‘established’ in this sense seems to imply ‘can’t be eradicted’, which makes the question kind of meaningless. If established just means ‘viable breeding population’ then there are numerous cases of eradication of established invasive animal species around the world.

A somewhat related question that I’ve been meaning to ask one of these days – how long does it take after an invasive plant or insect species arrives before the indigenous critters either develop defense mechanisms or begin finding them tasty?

For example, purple loosestrife , despite being a rather attractive plant, is regarded as quite a nuisance in North America because it replaces marsh vegetation with monocultures by outcompeting with it. One approach of eradicating loosestrife has been to import beetles that feast upon it. How long does a plant have to be in an area before the local beetles and insects develop a taste for it.

Similarly, Japanese beetles got released in the U.S. and have made themselves quite unwelcome. I know from experience that chickens find them very tasty. How come local birds haven’t discovered that a slow-moving nummy new treat has arrived in the neighborhood?

Mickey Rourke?

edible Dormice?? :eek:

I’ve heard that snails and sparrows were deliberately imported to America. But I heard it from my Dad, who had a tendency to pick up urban legends. Anyone know if there’s any truth to either?

Haven’t heard of an invasive species being eradicated. We have mitten crabs in the Sacramento/San Joaquin Delta. There are rumors that they’re in the process of establishing a boom and bust cycle. They steal bait and burrow into the sides of levees, weakening them. So any tips on eradicating them would be welcomed by a lot of people.

There are also rumors that the local sturgeon are learning to eat mitten crab.

That’s a really complex question, since the potential predators and the possible defences vary so much.

At one end of the spectrum the answer it’s instantaneous. This will most likely occur when the indigenous predator is a vertebrate and so has a high learning capacity and a willingness to try new food sources. It will also be high if the invasive species has nor particular defences. So as an example when cactoblastis moths were introduced to Australia and America they were being preyed upon by indigenous bird species almost immediately. They have no particular defence against predators beyond hiding and a slightly unpleasant taste, neither of which stopped hungry birds from figuring out they were edible. In the same way any invasive but edible grass species will be immediately eaten by the first indigenous deer or whatever happens to walk past.

Vertebrates are smart, they experiment and learn and because of that they can learn to deal with novel food source in under one generation.

As you move up the scale you get instances where the predator is a vertebrate but the introduced species has some sort of effective defence. Nit an insect or plant, but the cane toad in Australia is a good example of this situation. The toad is poisonous when eaten whole. For many decades after its introduction it had no predators at all. However by about 40 years after it was introduced several bird and one mammals species had learned that the toxin is concentrated in the skin and that the muscles and some internal organs weren’t toxic enough to cause problems. These predators have taken to skinning or disembowelling the toads, and the behaviour is spreading.

At the top end there are instances where the predators are insects and the invader has chemical defences. Insects don’t learn much. They tend to select food based purely on instinctive programming, and if a food source doesn’t smell or look like food they won’t touch it. That doesn’t mean insects never touch invaders. I’m sure that indigenous ants will happily chow down on cactoblastis caterpillars if they can, but that’s because the will eat anything that moves too slow, it’s not learning or adaptation. In most instances insects will either be pre-adapted to attack an invader and will do so immediately, or they will never learn. Waiting for local beetles to attack a weed is hopeless. An insect species could be left with a food source forever and it will never eat it until a mutation occurs that causes it to try, and such mutations are rare.

That’s further complicated by any possible chemical or physical defences on the plant. Even if a mutation did occur that would prompt local beetles to be attracted to the smell of loosestrife the plant will simply poison any beetle that tries to eat it. For the beetles to have any effect they would need to mutate to deal with the poison first, with absolutely no evolutionary benefit, and then later mutate to be attracted to the smell of the plant. Needless to say that’s pretty unlikely to happen.
Exotic beetles have an advantage because they evolved alongside the plant. They began feeding on its ancestors when it wasn’t poisonous and every time the plant evolves to alter the toxin just a little the beetles just have to evolve a little two. The two species progress together with neither side pulling so far ahead that the other can’t catch up. When the plant becomes an exotic weed the local beetles are so far behind in the race that it would take multiple massive mutations to give them a chance unless the plant is very closely related to an indigenous species that the beetles already feed on.

That’s not the problem, I’m sure that if they aren’t toxic they are eaten by local birds. The problem is that the beetle at home is kept in check by thousands of bacterial diseases, viruses, parasitic worms, insect predators and competitor insects that have aevolved alongside it. Back home the trees have alo evolved to stop the beetle eatng them in avariety of ways. Here it has a smorgasboard of defenceless trees, no diseases, no competitors that can handle it and no insects that eat it. T heonly thing that it has to worry about is a few birds. But bords only lay a few eggs a years, while the beetles lay millions, and th ebirds can’t just breed up by eating bettels because come winter all th birds willstrev to detah while millions of bettle eggs hatch into a wolr dwith very few birds. The birds on their own can’t keep up no matte rhow many beetles they eat, they need othe rpredators and diseases to help them.


Considered quite a delicacy by the Romans apparently. All sorts of things were considered delicacies by the Romans of course.

“Lark’s tongues! Wren’s livers! Chaffinch’s brains! Jaguar’s earlobes! Wolf’s nipple chips! Get them while they’re hot, they’re lovely. Dromedary pretzel verily after dinner! Tuscany fried bats!”

House sparrows and various snail species have been introduced to the US.

Ah. So we weren’t snail-free before the great escape. Good to know.


*Yes, that was tasteless. I should be ashamed.

Onna stick!

Mmmmm. Wolf’s nipple chips. Just like grandma used to make.