Invasive alien species in Switzerland - Schweizer ...

An inventory of alien species and their threat to biodiversity and economy in Switzerland FOEN 2006 116
Switzerland. The total number of species in these families found in Switzerland is 33,
so about 21 % are introduced. This is a rather high percentage, as will be seen below. It
seems that slugs are very good at hiding in plant material, decaying material and other
commodities and are widely transported. Today there are three established introduced
bivalves, which is about 11 % of the total of 28 species found in Switzerland. Probably
six out of the 50 freshwater snail species are alien (12 %). Finally, the large group of
terrestrial snails (terrestrial molluscs excluding the four families of slugs mentioned
above) comprise approximately 160 species, of which a mere three species (2 %) are
introduced. With the exception of the slugs, the pattern that emerges might be a random
phenomenon due to small sample sizes; whereby a few introductions of species in
smaller groups form a higher percentage of the total fauna. The extreme would be a
randomly introduced species from a group comprising one species, which would form
100 % of the fauna of that particular group. The total percentage of established molluscs
is about 6.9 % (19 of 274 species).
A comparison of the established mollusc species in Switzerland and Austria shows a
very similar picture; the percentage of introduced mollusc species is 6.9 % in Switzerland
and 7.6 % in Austria (Essl and Rabitsch, 2002). Of course, the total number of
species differs because Austria is about twice the size of Switzerland (83,855 km 2
compared to 41,285 km 2 ). About 435 mollusc species occur in Austria, including 33
aliens. Even more established alien mollusc species are recorded in Germany, about 40,
but five of those are marine (Geiter et al., 2002). There is a remarkable overlap of the
alien species in the three countries, emphasizing the regular introduction of some
species (in some cases using the same frequent pathways).
Most of the established alien mollusc species originate within Europe (Tab. 5.1),
although the exact origin of some Ponto–Caspian species is not known, so whether
these species originate in Europe or Asia may be disputable. Only five (about a quarter)
of the species travelled a long distance to Switzerland. The majority have apparently
profited from short-distance transport of commodities between European countries.
Tab. 6.1 > Origin of alien molluscs established in Switzerland.
Origin
Europe 13
Asia 2
North America 2
Switzerland 1
New Zealand 1
Total 19
No. species