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2 Pathways in Animal Invasions
Wolfgang Nentwig
2.1 Natural Dispersal Versus more Recent Invasions
Two main ways of dispersal of species can be distinguished: natural dispersal
and anthropogenic spread, either indirectly or directly. Natural spread is usually
slow and occurs within evolutionary times, it hardly crosses biogeographic
borders, and is mostly undirectional. Anthropogenic dispersal is
enabled or facilitated directly by human activities. This includes domestication
and the worldwide spread of selected species, releases into the wild of
suitable game, and escapes from captivity. Humans use animals for nutrition
in multiple ways (farming, game, aquaculture and mariculture) and, as
humans settle in the world, other species accompany them. More recent motivations
to spread species worldwide include the demand for luxury and exotic
products (e.g. fur farms), biological control and the pet trade. The main directions
of anthropogenic dispersal until the 19th century were from Europe to
the European colonies and many other parts of the world. Later, with the
increasing independence of numerous countries, with growing world trade,
and also with the actual step of globalization, species have been distributed to
and from everywhere in the world.
In the past, many introductions occurred intentionally, e.g. as game or as
“enrichment” of a new environment, or they were accepted as unavoidable.
Looking back today, the lack of even basic ecological knowledge is astonishing
and the naive attitude of even scientists is frightening. By contrast, unintentional
introductions concern many smaller species such as arthropods,
parasites of other species, as contaminants of goods or stowaways on means of
transportation.
Ecological Studies,Vol. 193
W. Nentwig (Ed.)
Biological Invasions
© Springer-Verlag Berlin Heidelberg 2007