Friday, 25 May 2012

When introductions go bad

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:

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.

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

Red Squirrel image source: Sarah Stephen


David said...

Very interesting, and lovely photo of the squirrel!
Tilapia are common on Brazilian menus and I suppose I assumed they were already farmed. By all accounts they escape easily so I hope they don't get the chance!

jeanvitule said...

About Tilapias and other non native fish:
I think the basic problem is that current legislation allows the cultivation of non-native fish in cages networks only in environments where the NON NATIVE species is demonstrably established, which is not the case in most environments dammed in the country, especially in the basins in the West and North portions of the Brazil.
Apart from this obvious mismatch, the major concern is about the possibility of massive releases of non-native fishes into Brazilian ecosystems. There are numerous scientific publications showing that negative impacts follow the establishment of non-native fish, including impacts caused by tilapia (a target species) in Brazilian aquatic ecosystems (e.g. Vitule 2009 and references therein), problems neglected in the law project (PL). Especially, PL neglected broad and basic aspects concerning fish invasionlike: there is no safe confinement in aquaculture, and the activity has been considered the main vector releasing non-native organisms around the world (Naylor et al., 2001). Fish escapes are inevitable, and cage aquaculture may create a constant flow of propagules into the wild , establishment, spread and invasions. Certainly, aquaculture may affect invaders dynamics, which in turn determine impacts. Finally, cages will be installed in reservoirs, environments that facilitate the invasion process (Johnson et al. 2008), so establishment, dispersion and impacts will be magnified triggering to colossal invasion events across South America, because reservoirs are in all large basins of the continent and fish do not recognize political borders.

If the real danger of species introductions is minimized
because of insufficient and unreliable data, or misguided
ecological pragmatism, carte blanche is in fact provided
to decision-makers or organizations who think only
about immediate profit that introductions can bring,
without considering longer term losses. Those losses
will be tremendous and experienced by all future
generations, especially those who live in megadiverse
tropical countries.(Lövei at al 2012).
Jean Vitule

Ruth Stephen said...

Thank you David for your comment. De. Jean Vitule, the author of the correspondence in Nature, has kindly commented. In a nutshell, as your correctly pointed out, culture of non-native species indeed takes place in areas where such fishes are 'established ' but not in those environments that are dammed in Brazil.

Ruth Stephen said...

Thank you for your comments Dr. Vitule. Many thanks for highlighting this issue. We will look forward to hearing more about the fate of the proposed law in due course. We wish you all the best in your research

Anonymous said...

Dear Ruth,

You are welcome!

Thank you for use our correspondence.

Thanks on behalf of my co-author.



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