The distribution of diversity: challenges and applications
61
the classic examples of this is Spix ’ s macaw ( Cyanopsitta
spixii ), a magnifi cent neotropical parrot that was collected into extinction, but which clings on to existence
in the aviaries of private individuals and institutions
(Juniper, 2003 ).
5 Local extinction or ‘ extirpation ’ occurs when a species
has disappeared from a clearly delimited geographical
area (often relating to a geographical or physical
boundary), but where extant, free - living populations
exist outside that area. A classic example is the red kite
( Milvus milvus ), which disappeared from England in
the late 19th century, but was successfully reintroduced in the late 1980s and early 1990s using populations sourced from Spain, Sweden and Wales (Evans
et al ., 1999 ). Another dramatic example that combines
properties of both ecological and local extinction is the
still - experimental reintroduction of the Californian
condor ( Gymnogyps californianus ) into the vicinity of
the Grand Canyon in western North America, a region
that had been without condors since the late
Pleistocene. While the drivers of local extinction are
the same as the drivers of global extinction, the
response of the conservation movement may be radically different and, for collectable species, global rarity
may even enhance the pressure on the remaining
populations.
6 True extinction can be defi ned as occurring when
there is no reasonable doubt that the last population is
extinct and where no captive population or genetic
material exists. One of the most high profi le recent
examples of this is the Yangtze River dolphin, or baiji
( Lipotes vexillifer ), whose disappearance was reported
after extensive surveys in November and December
2006 (Turvey et al ., 2007 ). Ladle and Jepson (2008)
distinguish between extinctions that occurred before
(e.g. the dodo, Steller ’ s sea cow) and after the advent
of the global conservation movement, because of the
differing degrees of associated knowledge, certainty
and conservation action surrounding such events
(Table 4.2 ).
So how many species have humans already driven
to extinction in the recent past, and how many may go
extinct in the future? First, to deal with the recent past,
fi gures given by different authorities vary depending
on the criteria adopted, so the values given in Table 4.3
should be taken as of largely indicative value. They are
certain to signifi cantly underestimate the true magnitude of extinction in the last four centuries.
For example, based on extrapolations from historical
records and sub - fossil remains, it has been suggested
never been surveyed or which have not recently been
surveyed. In an island biogeographical context, where
biologists are interested in the turnover of species
through time on a single island, the problem is termed
pseudo - turnover, meaning that a species has appeared
to go extinct from that island and then re - immigrate
from elsewhere when it was actually present throughout, but this was not detected due to inadequacies of
survey efforts. This problem has, for example, infl uenced estimates of extinction and turnover rates of
plants and of birds on the Krakatau Islands, Indonesia
(Bush & Whittaker, 1991 ; Thornton et al ., 1993 ).
3 Phoenix extinctions are of species that have the
potential to be resurrected through human ingenuity,
and they take at least two forms. The fi rst is where
species have been transformed by human action for the
purposes of domestication. Thus, although European
wild cattle ( Bos primigenius ) became extinct in the 17th
century, through back - breeding and artifi cial selection
of domesticated cattle, a wild - acting replicate of
the auroch is currently part of the ecology of the
Oostvaardersplassen nature reserve in Holland (Ladle
& Jepson, 2008). The term ‘ phoenix extinction ’ might
also be applied to the plains bison ( Bison bison ), which
hybridized extensively with domesticated cattle during
the late 1800s and early 1900s (Freese et al ., 2007 ), or
more recent attempts to create a quagga - like animal by
selectively breeding zebra.
The second form of phoenix extinction identifi ed by
Ladle and Jepson (2008) is where technology is able to
recreate extinct species using genetic material stored in
gene banks or extracted from preserved remains. This
idea has been around for decades and is already used
in agriculture for resurrecting different varieties of
domesticated species. However, recent advances in
genetic technologies have dramatically increased the
potential for scientists to recreate extinct species and
have stimulated public interest in this possibility. There
are currently no credible examples of such resurrections, although the whole mammoth genome has
recently been sequenced (Miller et al ., 2008 ), leading
to renewed speculation that such a technological feat
might one day be possible.
4 Ecological extinction refers to a species that persists
in captivity, but which is no longer found in the wild,
or occurs in densities so low that it ‘ no longer interacts
signifi cantly with other species ’ (Estes et al ., 1989 , p.
253). Alternatively, ecological extinction could be
described as the avoidance of complete extinction
through the intervention of captive breeding. One of
61
the classic examples of this is Spix ’ s macaw ( Cyanopsitta
spixii ), a magnifi cent neotropical parrot that was collected into extinction, but which clings on to existence
in the aviaries of private individuals and institutions
(Juniper, 2003 ).
5 Local extinction or ‘ extirpation ’ occurs when a species
has disappeared from a clearly delimited geographical
area (often relating to a geographical or physical
boundary), but where extant, free - living populations
exist outside that area. A classic example is the red kite
( Milvus milvus ), which disappeared from England in
the late 19th century, but was successfully reintroduced in the late 1980s and early 1990s using populations sourced from Spain, Sweden and Wales (Evans
et al ., 1999 ). Another dramatic example that combines
properties of both ecological and local extinction is the
still - experimental reintroduction of the Californian
condor ( Gymnogyps californianus ) into the vicinity of
the Grand Canyon in western North America, a region
that had been without condors since the late
Pleistocene. While the drivers of local extinction are
the same as the drivers of global extinction, the
response of the conservation movement may be radically different and, for collectable species, global rarity
may even enhance the pressure on the remaining
populations.
6 True extinction can be defi ned as occurring when
there is no reasonable doubt that the last population is
extinct and where no captive population or genetic
material exists. One of the most high profi le recent
examples of this is the Yangtze River dolphin, or baiji
( Lipotes vexillifer ), whose disappearance was reported
after extensive surveys in November and December
2006 (Turvey et al ., 2007 ). Ladle and Jepson (2008)
distinguish between extinctions that occurred before
(e.g. the dodo, Steller ’ s sea cow) and after the advent
of the global conservation movement, because of the
differing degrees of associated knowledge, certainty
and conservation action surrounding such events
(Table 4.2 ).
So how many species have humans already driven
to extinction in the recent past, and how many may go
extinct in the future? First, to deal with the recent past,
fi gures given by different authorities vary depending
on the criteria adopted, so the values given in Table 4.3
should be taken as of largely indicative value. They are
certain to signifi cantly underestimate the true magnitude of extinction in the last four centuries.
For example, based on extrapolations from historical
records and sub - fossil remains, it has been suggested
never been surveyed or which have not recently been
surveyed. In an island biogeographical context, where
biologists are interested in the turnover of species
through time on a single island, the problem is termed
pseudo - turnover, meaning that a species has appeared
to go extinct from that island and then re - immigrate
from elsewhere when it was actually present throughout, but this was not detected due to inadequacies of
survey efforts. This problem has, for example, infl uenced estimates of extinction and turnover rates of
plants and of birds on the Krakatau Islands, Indonesia
(Bush & Whittaker, 1991 ; Thornton et al ., 1993 ).
3 Phoenix extinctions are of species that have the
potential to be resurrected through human ingenuity,
and they take at least two forms. The fi rst is where
species have been transformed by human action for the
purposes of domestication. Thus, although European
wild cattle ( Bos primigenius ) became extinct in the 17th
century, through back - breeding and artifi cial selection
of domesticated cattle, a wild - acting replicate of
the auroch is currently part of the ecology of the
Oostvaardersplassen nature reserve in Holland (Ladle
& Jepson, 2008). The term ‘ phoenix extinction ’ might
also be applied to the plains bison ( Bison bison ), which
hybridized extensively with domesticated cattle during
the late 1800s and early 1900s (Freese et al ., 2007 ), or
more recent attempts to create a quagga - like animal by
selectively breeding zebra.
The second form of phoenix extinction identifi ed by
Ladle and Jepson (2008) is where technology is able to
recreate extinct species using genetic material stored in
gene banks or extracted from preserved remains. This
idea has been around for decades and is already used
in agriculture for resurrecting different varieties of
domesticated species. However, recent advances in
genetic technologies have dramatically increased the
potential for scientists to recreate extinct species and
have stimulated public interest in this possibility. There
are currently no credible examples of such resurrections, although the whole mammoth genome has
recently been sequenced (Miller et al ., 2008 ), leading
to renewed speculation that such a technological feat
might one day be possible.
4 Ecological extinction refers to a species that persists
in captivity, but which is no longer found in the wild,
or occurs in densities so low that it ‘ no longer interacts
signifi cantly with other species ’ (Estes et al ., 1989 , p.
253). Alternatively, ecological extinction could be
described as the avoidance of complete extinction
through the intervention of captive breeding. One of