114
of invasiveness. The authors suggest that successful invaders
might be able to use both, internal repositories as well as
external energy sources, during reproduction, allowing for
higher fecundity or extended breeding periods (Zeng et al.
2014). In some cases, seasonality also seems to have facilitated the establishment of NIS. Temporally shifted breeding
periods are for example believed to reduce competition
between early juveniles of native crabs and the invasive
European shore crab Carcinus maenas in Australia (Garside
et al. 2015).
Having a planktonic larval stage is a common feature of
many marine taxa, but it provides particular benefits for
establishing NIS by increasing their dispersal abilities. This
trait mostly affects the secondary regional spread after the
initial introduction of a species. Some marine NIS possess a
significantly longer duration of larval development compared to native species of the same taxonomic group, which
is regarded as a mean of further enhancing the dispersal
potential (Roman and Palumbi 2004; Viard et al. 2006;
Delaney et al. 2012; Katsanevakis et al. 2013). The choice of
recruitment sites by the last larval stages is often positively
influenced by chemical signals released by conspecifics (gregarious settlement), but for some successful invaders cues
from suitable habitat act as strong as recruitment enhancer as
conspecific cues. This mechanism has for example been
shown for the crab Hemigrapsus sanguineus and is believed
to enhance the species’ ability to colonize new habitats
(O’Connor 2007; Anderson and Epifanio 2009).
Resource utilization and food preference is another set of
traits, where successful invaders often show high levels of
plasticity. Omnivory (in animals) and the ability to quickly
adapt to a changed food supply is often observed (e.g., Blasi
and O’Connor 2016) and allows NIS to avoid food competition with native species of the same guild. On the other hand,
newly arrived species can also cause dietary shifts in native
species, being both, beneficial for themselves but detrimental
for the native competitor (Griffen et al. 2011).
A species physiology is an important component in determining its ability to take hold in a new habitat (Fig. 2). In
order for an invader to take hold and remain, it must pass
biotic and abiotic conditions, known as the “ecological filter” of the environment (Crowl et al. 2008). Abiotic factors
are the first part of the filter that NIS must endure. They must
be able to survive physiological adjustments and abiotic
stressors such as temperature, desiccation, and disturbance
(Olyarnik et al. 2009). Granted a species is able to endure the
abiotic factors, they must also be able to maintain performance and fitness through competition (Levine et al. 2004)
and predation (deRivera et al. 2005) with other species in the
environment. Failing to survive through this filter can prevent establishment or range expansion (Kelley 2014).
Temperature and salinity are two factors highly regarded
in limiting an organism’s ability to expand its range as a NIS,
as is the case in Mytilus studies (Pickens 1965; Helm and
Trueman 1967; Coleman and Trueman 1971; Stickle and
Sabourin 1979; Nicholson 2002; Braby and Somero 2006a).
Mytilus trossulus is native to the North Pacific, however, has
been replaced along the California coastline from the
Mexican border to Monterey Bay after the introduction of
Mytilus galloprovincialis, a Mediterranean native, to
Southern California via shipping in the 1900s (McDonald
and Koehn 1988; Geller 1999). A habitat mosaic exists in
San Francisco and Monterey Bay, which are both characterized by varying abiotic environmental conditions (Braby and
Somero 2006b). While the invasive mussel (Mytilus galloprovincialis) is genetically inclined to high temperature thermal tolerance, Mytilus trossulus is well adapted to areas
achieving a critical salinity level, making the matrix of habitats in Monterey and San Francisco Bay a mixed mosaic,
where otherwise Mytilus galloprovincialis had displaced it
along the southern coast given its thermal tolerance acclimation advantage (Braby and Somero 2006a).
In some cases, NIS are able to sustain populations in new
ranges despite not being physiologically capable of reproduction in the surrounding environment. This is a leading
hypothesis for the Chinese Mitten Crab Eriocheir sinensis in
the Baltic Sea. Though other theories exist, evidence suggests that the Elbe River estuary is a donor area for E. sinensis, and that individuals are migrating to the Baltic via the
Kiel Canal, traveling distances up to 1,500 km (Ojaveer et al.
2007). Under unfavourable combinations of temperature and
salinity, it has been shown that additional larval stages may
occur in E. sinensis (Ojaveer et al. 2007), which is a phenomenon unique among brachyuran crabs (Montú et al. 1996).
Other crab species have also shown regional adaptations to
physiological parameters. Populations of the European shore
crab C. maenas in the Baltic Sea (salinity 15) have shown a
higher capacity for hyper-regulation than populations of C.
maenas in the North Sea (salinity 30) (Theede 1969).
Competition, Facilitation and Parasitism –
Species’ Interactions
Wherever NIS are introduced, they develop interactions with
both native and other non-native species in their new habitat.
At the same time, detrimental interactions with species of
their native range, such as predators, parasites or pathogens,
may fall away in the invaded range (‘enemy-releasehypothesis’, see e.g., Jeschke et al. 2012; Papacostas et al.
2017). Either way, shifts in the interaction regimes of NIS
during the invasion process are probably among the most
important factors determining the long-term potential for a
successful establishment after initial introduction.
Many invasive species are known as strong competitors,
having negative effects on native species occupying the same
J. C. Geburzi and M. L. McCarthy
of invasiveness. The authors suggest that successful invaders
might be able to use both, internal repositories as well as
external energy sources, during reproduction, allowing for
higher fecundity or extended breeding periods (Zeng et al.
2014). In some cases, seasonality also seems to have facilitated the establishment of NIS. Temporally shifted breeding
periods are for example believed to reduce competition
between early juveniles of native crabs and the invasive
European shore crab Carcinus maenas in Australia (Garside
et al. 2015).
Having a planktonic larval stage is a common feature of
many marine taxa, but it provides particular benefits for
establishing NIS by increasing their dispersal abilities. This
trait mostly affects the secondary regional spread after the
initial introduction of a species. Some marine NIS possess a
significantly longer duration of larval development compared to native species of the same taxonomic group, which
is regarded as a mean of further enhancing the dispersal
potential (Roman and Palumbi 2004; Viard et al. 2006;
Delaney et al. 2012; Katsanevakis et al. 2013). The choice of
recruitment sites by the last larval stages is often positively
influenced by chemical signals released by conspecifics (gregarious settlement), but for some successful invaders cues
from suitable habitat act as strong as recruitment enhancer as
conspecific cues. This mechanism has for example been
shown for the crab Hemigrapsus sanguineus and is believed
to enhance the species’ ability to colonize new habitats
(O’Connor 2007; Anderson and Epifanio 2009).
Resource utilization and food preference is another set of
traits, where successful invaders often show high levels of
plasticity. Omnivory (in animals) and the ability to quickly
adapt to a changed food supply is often observed (e.g., Blasi
and O’Connor 2016) and allows NIS to avoid food competition with native species of the same guild. On the other hand,
newly arrived species can also cause dietary shifts in native
species, being both, beneficial for themselves but detrimental
for the native competitor (Griffen et al. 2011).
A species physiology is an important component in determining its ability to take hold in a new habitat (Fig. 2). In
order for an invader to take hold and remain, it must pass
biotic and abiotic conditions, known as the “ecological filter” of the environment (Crowl et al. 2008). Abiotic factors
are the first part of the filter that NIS must endure. They must
be able to survive physiological adjustments and abiotic
stressors such as temperature, desiccation, and disturbance
(Olyarnik et al. 2009). Granted a species is able to endure the
abiotic factors, they must also be able to maintain performance and fitness through competition (Levine et al. 2004)
and predation (deRivera et al. 2005) with other species in the
environment. Failing to survive through this filter can prevent establishment or range expansion (Kelley 2014).
Temperature and salinity are two factors highly regarded
in limiting an organism’s ability to expand its range as a NIS,
as is the case in Mytilus studies (Pickens 1965; Helm and
Trueman 1967; Coleman and Trueman 1971; Stickle and
Sabourin 1979; Nicholson 2002; Braby and Somero 2006a).
Mytilus trossulus is native to the North Pacific, however, has
been replaced along the California coastline from the
Mexican border to Monterey Bay after the introduction of
Mytilus galloprovincialis, a Mediterranean native, to
Southern California via shipping in the 1900s (McDonald
and Koehn 1988; Geller 1999). A habitat mosaic exists in
San Francisco and Monterey Bay, which are both characterized by varying abiotic environmental conditions (Braby and
Somero 2006b). While the invasive mussel (Mytilus galloprovincialis) is genetically inclined to high temperature thermal tolerance, Mytilus trossulus is well adapted to areas
achieving a critical salinity level, making the matrix of habitats in Monterey and San Francisco Bay a mixed mosaic,
where otherwise Mytilus galloprovincialis had displaced it
along the southern coast given its thermal tolerance acclimation advantage (Braby and Somero 2006a).
In some cases, NIS are able to sustain populations in new
ranges despite not being physiologically capable of reproduction in the surrounding environment. This is a leading
hypothesis for the Chinese Mitten Crab Eriocheir sinensis in
the Baltic Sea. Though other theories exist, evidence suggests that the Elbe River estuary is a donor area for E. sinensis, and that individuals are migrating to the Baltic via the
Kiel Canal, traveling distances up to 1,500 km (Ojaveer et al.
2007). Under unfavourable combinations of temperature and
salinity, it has been shown that additional larval stages may
occur in E. sinensis (Ojaveer et al. 2007), which is a phenomenon unique among brachyuran crabs (Montú et al. 1996).
Other crab species have also shown regional adaptations to
physiological parameters. Populations of the European shore
crab C. maenas in the Baltic Sea (salinity 15) have shown a
higher capacity for hyper-regulation than populations of C.
maenas in the North Sea (salinity 30) (Theede 1969).
Competition, Facilitation and Parasitism –
Species’ Interactions
Wherever NIS are introduced, they develop interactions with
both native and other non-native species in their new habitat.
At the same time, detrimental interactions with species of
their native range, such as predators, parasites or pathogens,
may fall away in the invaded range (‘enemy-releasehypothesis’, see e.g., Jeschke et al. 2012; Papacostas et al.
2017). Either way, shifts in the interaction regimes of NIS
during the invasion process are probably among the most
important factors determining the long-term potential for a
successful establishment after initial introduction.
Many invasive species are known as strong competitors,
having negative effects on native species occupying the same
J. C. Geburzi and M. L. McCarthy