Eastern grey squirrels in Europe
[2] They were first introduced into England, in a concerted way, in 1876,[3] and through rapidly growing population and further introductions they spread to the rest of Great Britain by the early to mid-20th century.
[1] Genetic studies have shown that human intervention-- released pets and intentional dispersal--may play a much larger role in the spread of grey squirrels than previously believed.
They were first introduced into England, in a concerted way, in 1876,[3] and through rapidly growing population and further introductions they spread to the rest of Great Britain by the early to mid-20th century.
[8] This efficiency in the spread of grey squirrels can be explained by the enemy release hypothesis, which is when the invading species has better survival because its natural predators are not present.
[8] This is most likely due to the fact that reds and greys participate in direct competition for limited resources, suggesting there is no niche partitioning occurring.
[8] This direct competition also explains a decrease in juvenile recruitment and reproductive success, as immature reds will die due to lack of resources before reaching sexual maturity.
[6] The full consequences of these interactions cannot be completely determined, though the difference in population density and weight of the two species may have an effect on energy flow in ecosystems.
In those populations, the greys mainly feed on "seeds, fruits, buds, flowers and, occasionally, on insects, switching from one resource to another according to seasonal availability".
[7] For example, Garry oak trees on Vancouver Island have become endangered due to urban development and the presence of invasive species including the grey squirrel.
[7] Bark stripping makes branches weaker and more susceptible to being broken off by wind or animals and can also cause secondary infection that may lead to death.
[7][8] Bark stripping makes trees more susceptible to red band needle blight (RBNB), which is caused by the asexual stage of the fungus Dothistroma septosporum.
[9] The models examined potential corridors that would allow grey squirrels to invade France and Switzerland and the time scale of such invasions.
[12] In 1991, eradication of a grey squirrel population in Piedmont was attempted via trapping and euthanasia; however, this effort was suspended for three years after animal rights groups filed a lawsuit.
[15][16] Although the negative consequences of introduction of non-native species are generally known in the scientific community, the majority of the public is unaware of the effects on native ecosystems.
[17] Effective control of the spreading of grey squirrels throughout continental Europe will require a coordinated approach of many nations, and ecologists recommend public education and trade restrictions as primary means to prevent new introductions of non-native species.
[2] Selectively timed culls, or removal of a percentage of the breeding individuals, of grey squirrel populations can help control and prevent tree damage.
