measures to extirpate the invaders directly (e.g. manual removal). We highlight that
best practices for the management of invaders in railway-related systems may be
difficult to generalize and that they may have to be considered on a case-by-case
basis. We end by stressing that research on railways in the context of biological
invasions remains scarce, and that fundamental knowledge for understanding the
relative importance of this transport system in the dispersal of species and on how
this process should be dealt with remains largely lacking.
Keywords Biological invasions Á Stowaway species Á Verges Á Invasibility
Introduction
Nowadays non-native species are widespread around the world. These species,
which have been moved beyond the limits of their natural ranges by human
activities, include not only most farm animals and plants, forestry species and pets,
but also many unwanted organisms such as mosquitoes, weeds, fungus and bacteria. Although most of these species perish soon after arriving at the new area, or
once humans cease to care for them, a few do form wild populations and become
part of the ecosystems (Williams and Newfield 2002). These species, often called as
“invasive,” are now one of the most important causes of global change, being
responsible for the decline and extinction of native species, economic losses, and
human health problems (Simberloff et al. 2013).
Humans have been moving species since pre historic times (Di Castri 1989), but
the number of biological invasions and the magnitude of their impacts in the last few
decades is unprecedented (Ricciardi 2007). This is to a great extent the result of the
recent large scale expansion of the transportation network and of the increasing
exchange of commodities to a nearly global coverage (Hulme 2009). Because of this,
most of the earth’s surface is now within reach of non-native species. Moreover, the
volume and diversity of the cargo and number of passengers now being transported is
also much greater than in any period in the past (Hulme 2009). This allows for a
greater diversity of species being introduced in new areas as well as a greater number
of their propagules, which increases both the number of potential invaders and their
ability to establish (Lockwood et al. 2009). Finally, the latest technical advances in
transportation allow species to move much faster. Even the least suspicious species,
e.g. those that are more environmentally sensitive, may become invasive in remote
regions of the original distribution (Wilson et al. 2009). In summary, as the extent,
volume, and efficiency of the transportation of people and freight increase, the burden
of biological invasions should also increase (Bradley et al. 2012).
Hulme et al. (2008) distinguish three main mechanisms by which
human-activities cause the dispersal of non-native species: (1) through importation
as a commodity or with a commodity; (2) as stowaways, i.e. through a direct
influence of a transportation vehicle; and (3) by means of natural dispersal along
artificial infrastructures, such as water canals, roads, and, especially relevant for our
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F. Ascensão and C. Capinha
best practices for the management of invaders in railway-related systems may be
difficult to generalize and that they may have to be considered on a case-by-case
basis. We end by stressing that research on railways in the context of biological
invasions remains scarce, and that fundamental knowledge for understanding the
relative importance of this transport system in the dispersal of species and on how
this process should be dealt with remains largely lacking.
Keywords Biological invasions Á Stowaway species Á Verges Á Invasibility
Introduction
Nowadays non-native species are widespread around the world. These species,
which have been moved beyond the limits of their natural ranges by human
activities, include not only most farm animals and plants, forestry species and pets,
but also many unwanted organisms such as mosquitoes, weeds, fungus and bacteria. Although most of these species perish soon after arriving at the new area, or
once humans cease to care for them, a few do form wild populations and become
part of the ecosystems (Williams and Newfield 2002). These species, often called as
“invasive,” are now one of the most important causes of global change, being
responsible for the decline and extinction of native species, economic losses, and
human health problems (Simberloff et al. 2013).
Humans have been moving species since pre historic times (Di Castri 1989), but
the number of biological invasions and the magnitude of their impacts in the last few
decades is unprecedented (Ricciardi 2007). This is to a great extent the result of the
recent large scale expansion of the transportation network and of the increasing
exchange of commodities to a nearly global coverage (Hulme 2009). Because of this,
most of the earth’s surface is now within reach of non-native species. Moreover, the
volume and diversity of the cargo and number of passengers now being transported is
also much greater than in any period in the past (Hulme 2009). This allows for a
greater diversity of species being introduced in new areas as well as a greater number
of their propagules, which increases both the number of potential invaders and their
ability to establish (Lockwood et al. 2009). Finally, the latest technical advances in
transportation allow species to move much faster. Even the least suspicious species,
e.g. those that are more environmentally sensitive, may become invasive in remote
regions of the original distribution (Wilson et al. 2009). In summary, as the extent,
volume, and efficiency of the transportation of people and freight increase, the burden
of biological invasions should also increase (Bradley et al. 2012).
Hulme et al. (2008) distinguish three main mechanisms by which
human-activities cause the dispersal of non-native species: (1) through importation
as a commodity or with a commodity; (2) as stowaways, i.e. through a direct
influence of a transportation vehicle; and (3) by means of natural dispersal along
artificial infrastructures, such as water canals, roads, and, especially relevant for our
66
F. Ascensão and C. Capinha