Look at the maps below ...
At first you might panic and think "Mr Miller did not teach us about squirrels ... I don't remember it being on the syllabus!". However, after a couple of seconds reflection, you will realise that your knowledge of these rodents is not what the examiner is seeking to test. Now look at the maps and think ...
Now, describe the trends shown in the distribution of red and grey squirrels in the British Isles over the last 60 years.
You should be able to easily spot ...
- the rapid growth of the grey from the southeast, moving north into the rapidly dwindling territories of the reds.
- The 'buffer zone' between the two distinctive territories.
- The fact that no squirrels appear to live on the west coast of Ireland or Scotland.
- The reds did not like some more remote areas such as Anglesey, the Gower or Pembrokeshire in 1945, but the greys seemed happy to invade here too..
- No squirrels live on the Isle of Man
- The greys are still yet to lay a paw on the Isle of Wight
Now the next part of a scholarship question would be to explain why these distribution patterns and trends have occurred. Again panic ye not, as the examination will usually provide some text which will have information about the grey squirrel invasion in it ... such as this ...
The grey squirrel was introduced to England, Scotland and Ireland from North America in the Victorian era. It has colonised 90% of England and Wales and has expanded from its initial sites in Scotland.
In Britain it has few natural predators and has successfully adapted to British lowland conditions. It is omnivorous, breeds strongly and is an aggressive settler, equally at home in urban parks and the countryside.
Grey squirrels are vectors (carriers) of the squirrelpox virus for which no vaccine is presently available. The virus is deadly to red squirrels but does not affect the host. This is cited as an “example of how diseases carried by invading species can act as biological weapons and speed up their conquest of native species.”
The threat to the economy
It is estimate that grey squirrels have cost the British economy £14 million per annum according to a study published by the international scientific organisation CABI for DEFRA, Scottish Government and the Welsh Assembly – The Economic Cost of Invasive Non-Native Species on Great Britain.
The threat in Europe
The future spread of the grey squirrel into France, Switzerland and eventually other neighbouring countries would pose a significant future problem for commercial forestry, biodiversity and a threat to native wildlife such as the European red squirrel.
The grey squirrel is now posing a serious threat to the great forests of northern Italy, France, Switzerland and Germany.
From this you should be able to come up with ...
- a theory for the changing distributions shown on the map (focusing on the squirrelpox theme)
- be able to predict the likely pattern in 2025, assuming that people do not intervene.