My first sighting of the red squirrel was in Camperdown Park in Dundee in 2003. I remember that scene vividly. I had since tried desperately to see this elusive animal again but to no avail, save a brief sighting, again in Camperdown Park, in Autumn 2010. This is because although red squirrel, which is native to UK and is protected in Europe, is outnumbered by its foreign relative, the grey squirrel that was introduced to the UK from America. Grey squirrel has several competitive advantages including its resistance to squirrel parapox virus which is fatal to the red (grey squirrels are vectors), increased fecundity, and greater ability to digest a wider variety of food. In fact, the future of the red squirrel in the British Isles is rather precarious. The Forestry Commission estimates that there there are only 140,000 red squirrels compared to over 2.5 million greys.
Recently during a holiday near Lake Geneva, Switzerland, I encountered 2 red squirrels and 1 black squirrel (resembled the red squirrel with respect to the ear tufts, but with a black/grey rather than red coat). You can see a video here in Youtube: http://www.youtube.com/watch?v=g4SqcK9CME8
There is a lot of debate on how the introduction of alien species can affect the native species and tilt ecosystems, but studies indicate that certain ecosytems could be more vulnerable that others. As early as 1958, Charles Elton claimed that ecosystems with higher species diversity were less subject to invasive species as there are fewer available niches. A recent paper by Eisenhauer et al shows that species diversity could stabilise communities during invasions. It appears as if biodiversity of ecosystems provides increased resilience against onslaughts including that by foreign invaders. Caution should be exercised when foreign species are introduced. In light of these observations, a proposed law in Brazil is of importance. A recent correspondence in Nature by Vitule et al (May 2012) warns of the repecussions of a new law that, if approved, would allow farming of foreign fish species in cages. The fishes that are being considered for introduction are tilapia and carp. The authors warn that the indigenious aquatic ecosystem would be disrupted if these introduced species were to escape and would jeopardise the aquatic biodiversity which is already fragile due to human activities such as pollution and construction.
References:
Vitule JR (2012). Ecology: Preserve Brazil's aquatic biodiversity. Nature, 485 (7398) PMID: 22596145
Eisenhauer N, Scheu S, & Jousset A (2012). Bacterial diversity stabilizes community productivity. PloS one, 7 (3) PMID: 22470577
http://www.europeansquirrelinitiative.org/the_threat.html
Red Squirrel image source: Sarah Stephen
