Invasive alien species in Switzerland - Schweizer ...

An inventory of alien species and their threat to biodiversity and economy in Switzerland FOEN 2006 54
2.4 Amphibians – Amphibia
Currently 20 amphibian species are found in Switzerland. One species (Rana ridibunda
Pallas), i.e. 5 % of the total Swiss species number, is introduced and established and
will be discussed below and in a Fact Sheet. A second species has been relocated
within Switzerland (Triturus carnifex (Laurenti)) and a third species is found occasionally
but has not yet been able to establish a population, i.e. the North American bullfrog
Rana catesbeiana Shaw (Table 2.5).
The marsh frog (Rana ridibunda) (see Fact Sheet) is the only introduced alien amphibian
species at the national level. It was introduced between 1920 and 1950, probably
from Hungary, as was the case with specimens released in the UK (Zeisset and
Beebee, 2003). The most probable explanation for the introductions is that they were
imports for human consumption. The marsh frog has now established with a wide
distribution in Switzerland, mainly in the west and the Valais and in the north-eastern
region. The species should not be supported, as native amphibian species are, by local
conservation groups, and releases on conservation grounds or as a food resource need
to be stopped. The role of the genetic peculiarities in the green frog complex are not
fully understood, but in most places where the marsh frog is increasing the other two
related species are decreasing. Thus, a displacement is evident.
Another species introduced into a new range is the Italian crested newt (Triturus
carnifex) (see Fact Sheet), which is native to the south of Switzerland (Ticino) but was
introduced to the canton of Genève. Genetic studies showed that the Genève population
is closest genetically to a population in Tuscany, Italy (Arntzen, 2001). Most probably
the species was imported for zoological experiments and released into a pond at the
University of Genève. It completely replaced the closely related great crested newt
(Triturus cristatus (Laurenti)) in that area. However, it is a complex situation and there
is hybridization between the two species. The distribution and spread of the Italian
crested newt should be monitored to provide information for future decisions about this
species and its threat.
The American bullfrog (Rana catesbeiana) (see Fact Sheet) has not (yet) colonized
Switzerland, but there are some recent unconfirmed records of the species. However, it
is established in the neighbouring countries of Germany, France, and especially Italy in
the Po valley with some rapidly expanding populations. Research has demonstrated its
high potential to cause a decline in native amphibians and reptiles. Thus, bullfrogs
should not be tolerated in the wild. Monitoring of suspect water bodies and raising
awareness in the human population for this potential menace to native biodiversity is of
high priority.
In Switzerland only one frog is introduced and established, this is 5 % of the 20 amphibian
species currently found in Switzerland. In Austria (Schuster and Rabitsch,
2002) and Germany (Geiter et al., 2002) no established amphibians are listed, although
it is possible that the American bullfrog has established unnoticed in the recent past –