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E.J. Cook et al.
changes caused a reduction in survivorship of key taxa that supported higher trophic
levels, such as migratory shorebirds (Neira et al. 2006).
Tilapia has been used worldwide as an aquaculture species and has escaped in
many regions where they are cultured (Peterson et al. 2005). Tilapia can significantly
alter the ecosystem they invade, yet the impact is often hard to predict (Figueredo
and Giani 2005). For example, the Redbelly tilapia (Tilapia zilli) was accidentally
introduced into a power plant reservoir in North Carolina, where it reduced all
aquatic macrophytes through grazing, which coincided with a dramatic decline in
native fishes (Crutchfield 1995). The Common carp (Cyprinus carpio) has been
widely translocated around the world for aquaculture purposes and through unintentional introductions is now a successful invader in parts of Europe, Asia, Africa,
North, Central and South America, Australia and Oceania (Lever 1996; FAO 2002).
Carp can reach high densities (1000 individuals ha
−1
) and biomass (3144 kg ha
−1
)
(Harris and Gehrke 1997) and this can result in reduced photosynthetic production
and visibility for visually feeding fish (Koehn 2004) through increasing the water
turbidity whilst feeding (Fletcher et al. 1985; King et al. 1997), a decline in the
abundance of aquatic plants (Fletcher et al. 1985; Roberts et al. 1995) and finally,
cause trophic cascades in shallow lakes (Khan et al. 2003).
5.3.3 Extinction of Native Flora and Fauna
There is no doubt that biological invasions are causing dramatic widespread
changes to communities and altering many ecological systems (Parker et al. 1999;
Ruiz et al. 1999; Levi and Francour 2004; Neira et al. 2005; Gribben and Wright
2006; Ruesink et al. 2006). However, many extinctions have been attributed to
biological invasions when there have been many other environmental factors
(eutrophication, habitat loss, land use changes, over grazing) which could have
played a key role in causing the decline of the native species (Gurevitch and Padilla
2004). Of the 762 species globally documented to have become extinct as a result
of human activities in the past few hundred years, < 2% list non-native species as
a cause (Gurevitch and Padilla 2004).
In many cases, species do not go “extinct”, but are lost from a large part of their
former range which greatly reduces and/or fragments the populations (Hobbs and
Mooney 1997). Non-native species have been identified as part of the problem and,
in combination with habitat loss, modification and degradation of the environment,
have lead to the loss of species in a particular region. For example, Fellers and
Drost (1993) resurveyed 16 historic sites and 34 other sites for the Cascade frog
Rana cascadae and only found two frogs at one site. The population extinction
was attributed to several factors, principally to the introduction of non-native
predatory fish, drought and habitat loss due to management activities (Hobbs and
Mooney 1997). The introduction of the Grass carp Catenopharyngodon idella, the
Bighead carp Aristichthys nobilis and the Taihu Lake noodlefish Neosalanx
taihuensis during the 1970s and 1980s to the southern provinces of Guangdong,
E.J. Cook et al.
changes caused a reduction in survivorship of key taxa that supported higher trophic
levels, such as migratory shorebirds (Neira et al. 2006).
Tilapia has been used worldwide as an aquaculture species and has escaped in
many regions where they are cultured (Peterson et al. 2005). Tilapia can significantly
alter the ecosystem they invade, yet the impact is often hard to predict (Figueredo
and Giani 2005). For example, the Redbelly tilapia (Tilapia zilli) was accidentally
introduced into a power plant reservoir in North Carolina, where it reduced all
aquatic macrophytes through grazing, which coincided with a dramatic decline in
native fishes (Crutchfield 1995). The Common carp (Cyprinus carpio) has been
widely translocated around the world for aquaculture purposes and through unintentional introductions is now a successful invader in parts of Europe, Asia, Africa,
North, Central and South America, Australia and Oceania (Lever 1996; FAO 2002).
Carp can reach high densities (1000 individuals ha
−1
) and biomass (3144 kg ha
−1
)
(Harris and Gehrke 1997) and this can result in reduced photosynthetic production
and visibility for visually feeding fish (Koehn 2004) through increasing the water
turbidity whilst feeding (Fletcher et al. 1985; King et al. 1997), a decline in the
abundance of aquatic plants (Fletcher et al. 1985; Roberts et al. 1995) and finally,
cause trophic cascades in shallow lakes (Khan et al. 2003).
5.3.3 Extinction of Native Flora and Fauna
There is no doubt that biological invasions are causing dramatic widespread
changes to communities and altering many ecological systems (Parker et al. 1999;
Ruiz et al. 1999; Levi and Francour 2004; Neira et al. 2005; Gribben and Wright
2006; Ruesink et al. 2006). However, many extinctions have been attributed to
biological invasions when there have been many other environmental factors
(eutrophication, habitat loss, land use changes, over grazing) which could have
played a key role in causing the decline of the native species (Gurevitch and Padilla
2004). Of the 762 species globally documented to have become extinct as a result
of human activities in the past few hundred years, < 2% list non-native species as
a cause (Gurevitch and Padilla 2004).
In many cases, species do not go “extinct”, but are lost from a large part of their
former range which greatly reduces and/or fragments the populations (Hobbs and
Mooney 1997). Non-native species have been identified as part of the problem and,
in combination with habitat loss, modification and degradation of the environment,
have lead to the loss of species in a particular region. For example, Fellers and
Drost (1993) resurveyed 16 historic sites and 34 other sites for the Cascade frog
Rana cascadae and only found two frogs at one site. The population extinction
was attributed to several factors, principally to the introduction of non-native
predatory fish, drought and habitat loss due to management activities (Hobbs and
Mooney 1997). The introduction of the Grass carp Catenopharyngodon idella, the
Bighead carp Aristichthys nobilis and the Taihu Lake noodlefish Neosalanx
taihuensis during the 1970s and 1980s to the southern provinces of Guangdong,