CHAPTER 9
Biological Invasions and
the Homogenization of
Faunas and Floras
Julian D. Olden
1
, Julie L. Lockwood
2 , and Catherine L. Parr
3
1 School of Aquatic and Fishery Sciences, University of Washington, Seattle, USA
2 Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ, USA
3 Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK
9.1 THE BIOGEOGRAPHY OF
SPECIES INVASIONS
In considering the distribution of organic beings
over the face of the globe, the fi rst great fact which
strikes us is, that neither the similarity nor the dissimilarity of the inhabitants of various regions can
be accounted for by their climatal and other physical
conditions … A second great fact which strikes us in
our general review is, that barriers of any kind, or
obstacles to free migration, are related in a close and
important manner to differences between the productions of various regions.
(Charles Darwin, 1859 , pp. 395 – 396)
9.1.1 The i nvasion p rocess
One of the fundamental elements of life on Earth is
change. Species appear through time via evolution and
disappear by the natural actions of environmental
change (e.g. volcanic eruptions, changing sea levels,
glaciation). Species have also regularly shifted their
geographical ranges in response to biological and physical forces, sometimes becoming less common and
other times becoming more widespread. In general,
however, the large majority of species are not distributed broadly, because individuals of most species have
limited dispersal capabilities.
These limitations on dispersal ability have produced
the interesting phenomenon that many, perhaps even
most, species do not occupy all of the areas of the world
in which they could quite happily thrive. Instead, they
are restricted to certain regions, where they are able to
interact with only those species with which they co -
occur. The limited geography of species is responsible,
in part, for the fantastic array of diversity that presently
carpets the Earth, as it provides opportunity for convergent evolution in disparate unconnected regions.
With the range expansion of modern humans, initially out of Africa, then across the globe, came the
possibility of human - mediated dispersal of a large
variety of other species. By this, we mean that humans
provided the conduit for individuals of some species to
disperse much farther abroad than they could naturally. Species were moved within, or on, humans as
parasites or disease organisms, in their household
goods as hitchhikers, as their livestock or working
animals, as their crop plants, as their pets, and as commodities themselves.
There is written evidence that intentional movements of species by humans traces back to ancient
Conservation Biogeography
Edited by Richard J. Ladle and Robert J. Whittaker
© 2011 Blackwell Publishing Ltd. ISBN: 978-1-444-33503-3
Biological Invasions and
the Homogenization of
Faunas and Floras
Julian D. Olden
1
, Julie L. Lockwood
2 , and Catherine L. Parr
3
1 School of Aquatic and Fishery Sciences, University of Washington, Seattle, USA
2 Ecology, Evolution, and Natural Resources, Rutgers University, New Brunswick, NJ, USA
3 Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, UK
9.1 THE BIOGEOGRAPHY OF
SPECIES INVASIONS
In considering the distribution of organic beings
over the face of the globe, the fi rst great fact which
strikes us is, that neither the similarity nor the dissimilarity of the inhabitants of various regions can
be accounted for by their climatal and other physical
conditions … A second great fact which strikes us in
our general review is, that barriers of any kind, or
obstacles to free migration, are related in a close and
important manner to differences between the productions of various regions.
(Charles Darwin, 1859 , pp. 395 – 396)
9.1.1 The i nvasion p rocess
One of the fundamental elements of life on Earth is
change. Species appear through time via evolution and
disappear by the natural actions of environmental
change (e.g. volcanic eruptions, changing sea levels,
glaciation). Species have also regularly shifted their
geographical ranges in response to biological and physical forces, sometimes becoming less common and
other times becoming more widespread. In general,
however, the large majority of species are not distributed broadly, because individuals of most species have
limited dispersal capabilities.
These limitations on dispersal ability have produced
the interesting phenomenon that many, perhaps even
most, species do not occupy all of the areas of the world
in which they could quite happily thrive. Instead, they
are restricted to certain regions, where they are able to
interact with only those species with which they co -
occur. The limited geography of species is responsible,
in part, for the fantastic array of diversity that presently
carpets the Earth, as it provides opportunity for convergent evolution in disparate unconnected regions.
With the range expansion of modern humans, initially out of Africa, then across the globe, came the
possibility of human - mediated dispersal of a large
variety of other species. By this, we mean that humans
provided the conduit for individuals of some species to
disperse much farther abroad than they could naturally. Species were moved within, or on, humans as
parasites or disease organisms, in their household
goods as hitchhikers, as their livestock or working
animals, as their crop plants, as their pets, and as commodities themselves.
There is written evidence that intentional movements of species by humans traces back to ancient
Conservation Biogeography
Edited by Richard J. Ladle and Robert J. Whittaker
© 2011 Blackwell Publishing Ltd. ISBN: 978-1-444-33503-3