Conservation planning in a changing world
175
population processes at the leading and trailing edges
may be very different.
Resources for conservation are generally severely
constrained, and the position of an area with respect
to geographical range margin is rarely used in most
conservation planning exercises; to achieve full representation of both core and marginal parts of species ’
ranges would be hard to achieve in practice for all but
a few species (Ara ú jo et al. , 2002b ).
The best strategy might also depend on the type of
threat. First, marginal populations might be expected
to persist longer than core populations in circumstances where contagious threats dominate (see Box
7.2 ). Second, core populations may persist longest
where a threat is diffuse across the species ’ entire geographical range. Third, our consideration of climate
change allows us to identify a scenario where current
seasonality. How will such a species respond to global
climate change in the next 50 years?
If the general trend, as anticipated by climate scientists, is a signifi cantly warmer world, the species may
have opportunity to extend its range, especially along
the northern margin. It will retreat from its southern
margin, remain bounded to the west by the sea, and
may either expand or contract along the eastern
boundary depending on the geographical pattern of
climate change and the particular climatic requirements of the species. Some marginal populations –
those at the trailing edge – are likely to become
unsustainable, while other marginal populations –
those at the leading edge – could well become crucial
for maintaining the viability of threatened species
(Figure 7.3 ). Depending on the ecology of the species
concerned, and especially the mobility of the species,
Figure 7.3 Hypothetical outcome of global climate change for a single species. The left hand panel shows the structure of
the range in the present day, with a dense occupancy of potential habitat around the core of the range and more fragmented
distributions near the northern and southern edges. A protected area in the south of the range provides a safe haven for the
species in the event of widespread land cover change threatening the species. With climate change, as shown in the right
hand panel, populations at the trailing edge of the range might be expected to fail, while the core range shifts northwards and
new populations form beyond the historical range margin. This assumes that the species concerned is initially at equilibrium
with the contemporary climate and is able to migrate as the climate changes. The populations shown in grey outline having
gone extinct, the species is no longer offered protection by the protected area.
175
population processes at the leading and trailing edges
may be very different.
Resources for conservation are generally severely
constrained, and the position of an area with respect
to geographical range margin is rarely used in most
conservation planning exercises; to achieve full representation of both core and marginal parts of species ’
ranges would be hard to achieve in practice for all but
a few species (Ara ú jo et al. , 2002b ).
The best strategy might also depend on the type of
threat. First, marginal populations might be expected
to persist longer than core populations in circumstances where contagious threats dominate (see Box
7.2 ). Second, core populations may persist longest
where a threat is diffuse across the species ’ entire geographical range. Third, our consideration of climate
change allows us to identify a scenario where current
seasonality. How will such a species respond to global
climate change in the next 50 years?
If the general trend, as anticipated by climate scientists, is a signifi cantly warmer world, the species may
have opportunity to extend its range, especially along
the northern margin. It will retreat from its southern
margin, remain bounded to the west by the sea, and
may either expand or contract along the eastern
boundary depending on the geographical pattern of
climate change and the particular climatic requirements of the species. Some marginal populations –
those at the trailing edge – are likely to become
unsustainable, while other marginal populations –
those at the leading edge – could well become crucial
for maintaining the viability of threatened species
(Figure 7.3 ). Depending on the ecology of the species
concerned, and especially the mobility of the species,
Figure 7.3 Hypothetical outcome of global climate change for a single species. The left hand panel shows the structure of
the range in the present day, with a dense occupancy of potential habitat around the core of the range and more fragmented
distributions near the northern and southern edges. A protected area in the south of the range provides a safe haven for the
species in the event of widespread land cover change threatening the species. With climate change, as shown in the right
hand panel, populations at the trailing edge of the range might be expected to fail, while the core range shifts northwards and
new populations form beyond the historical range margin. This assumes that the species concerned is initially at equilibrium
with the contemporary climate and is able to migrate as the climate changes. The populations shown in grey outline having
gone extinct, the species is no longer offered protection by the protected area.