Invasive Species - When Aliens Attack

Invasive species are devastating to the environment

Some people refer to a thing known as the ‘Rule of 10s’ this states that if 100 organisms are introduced to a new area 10 of them will be capable of surviving without input and of those 10 only  1 is going to cause a truly significant problem. So when you look at the numbers like that you have to ask yourself how likely invasive species are going to cause a problem. Well the problem is with better connection between everywhere in the world, thousands of invasive species have been able to move into new areas where they are all having very significant effects.

Now it’s hard to talk about invasive species in a general sense as every situation is different and is being dealt with differently.

An example of an invasive species in the UK is the grey squirrel, now this is something everyone who lives in the UK should already know about. In the 1870s they were introduced from the eastern side of North America which is their native range and since then they have expanded across the UK. In 2014 it was estimated that they possessed a population size of 2,520,000 within the UK. There are serious competitors to the native red squirrel this is due to their ability to store more fat than the red squirrels meaning that they are more likely to survive tough winters and be in a better condition afterward. Also their ability to produce more offspring whilst also living at higher densities, results in uncontrollable competition which the red squirrel is simply unable to match. It’s not just the competition they provide which has led to the decreased red squirrel numbers however, a virus known as squirrel pox has increased red squirrel decline by an estimate 17-20 times. This disease has been able to spread throughout the UK thanks to the extensive range of the grey squirrels which acts as a vector for the disease continuously introducing it to the few remaining isolated red squirrel populations.

A further example of an invasive species which has covered an entire country and has been mentioned before on this blog, is the mosquito fish Gambusia holbrooki, which was introduced into Australia in the 1920s, in the hope that it would control mosquito larvae. It is now present in every state except the Northern Territories and vastly affects the food web dynamics preying on aquatic invertebrates and breeding till it is the most dominant species in the pond. It also has an adverse effect on amphibians due to the fact that it attacks tadpoles and fin nips them which reduces the area of their tail and so prevents them from escaping from predators. There is not much to be done about this invasion as if a pond is drained gambusia always returns due to its resilience to droughts.

New Zealand as a country has been hit extremely hard by invasive species, owing to the fact that it has been separated from other land masses for so long means that in evolutionary terms many of the niches are occupied by organisms which are not adapted to predators and competition. This is issues being faced by many other isolated Islands such as Hawaii which distance for large land masses has made their ecology completely unique and so unable to cope with invasive species.

Within the US there are around +150 known invasive species which includes plants, reptiles, insects, molluscs, mammals, birds as well as pathogens (which are not usually thought of as an invasive species). One of the most well-known cases of invasive species within the US is the Burmese Pythons which can now be found in the Florida Everglades. A population which is believed to have become established due to the escape or release of captive pet, over 2000 were removed from 2002-2015 but it is believed that this effort made no kind of significant impact on population numbers despite extensive efforts.

Finally it is not simply invasive animals which cause problems and disrupt the stability of ecosystems, the introduction of invasive plants can cause equally as many problems to both native plants and animals. A quick example of this would be Japanese Knotweed which was introduced into Britain by the Victorians as an ornamental garden plant and has again spread from gardens into rural Britain, resulting in an estimated cost of £1.5billion to bring it under control.

As you can see invasive species are a serious issue and one which costs nearly every country billions of pounds a year through either loss of economic income or attempts in controlling and eradicating the invading species. In most cases however the damage has been done with many native species having become extinct due to the introduction of a new organism.

However there is always more work to be done on this front as with each new invasive species new threats are created and new diseases introduced resulting in different native species being put under pressure.

You can do something though, something as simple as thinking about what you are planting in your garden and whether its spread will be detrimental to your local environment will help. As well as this there are groups which are easily found in the internet local to you which need the help of volunteers to remove invasive species, so if you have some spare time that would be a good option to look into.

Thanks for reading

Side note – I only just brushed the surface of the effect that each of the invasive species mentioned in this post has and if you are interested there are countless studies being conducted, some of which have been running for many years to show the full extent of the introduction of an invasive species.

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