176
Planning for persistence in a changing world
detected small increases in the mean elevation for the
majority of species but, because some species showed
downward shifts, the average change across all species
was not signifi cantly different from zero. They also
recorded a small change in species composition, which
corresponded on average to a 29 m upward elevational
shift in the distribution of the avifauna. The relatively
small shift in elevation is surprising, given the considerable increase in temperature in the region ( ≈ 1 ° C),
which suggest that elevational shifts in regions of
complex topography may not always have a simple
relationship with increasing regional temperatures.
Understanding the temporal patterns of geographical range collapses is also critical for designing conservation interventions. Species with small and declining
distributions are at especially high risk of extinction,
and this observation has been used by the conservation
community to prioritize species based on their short -
term probability of extinction (Mace & Collar, 1995 ;
IUCN, 2001 ). The distributions of species change naturally over evolutionary time, with range sizes broadly
increasing following speciation and then, subsequently,
declining towards extinction (Figure 7.1 ; Gaston,
2003 ; Vrba & DeGusta, 2004 ), but human intervention dramatically steepens the trajectory of decline
towards extinction, and conservation activity is often
focused on those species in which the rate of change is
particularly great.
However, sometimes the fi nal trajectory to extinction may be so steep that it is too late for effective conservation action. Furthermore, applying conservation
effort only in the fi nal stages of a species ’ decline may
lead to a continuous cycle of ‘ crisis management ’
(Linklater, 2003 ) and may be an ineffi cient use of
resources (Bottrill et al. , 2008 ).
7.3 PREDICTING BIODIVERSITY
CHANGE
The foregoing discussion has revealed many examples
of long - term changes in species ’ distributions, and
these are likely to accelerate in the future as humans
increasingly dominate the ecology of the planet. As
environmental conditions change over time, species
could:
1 move to locations where their preferred conditions
are still found;
2 adapt in some way to the changing conditions; or
trailing - edge populations expand in their population
size and supply colonists for range expansion so that
they are no longer absolutely the periphery of the
species range.
In such a scenario, the pattern will follow a similar
geographical pattern to the contagion hypothesis, but
with two key modifi cations:
1 the pattern of range collapse will follow a climatically predictable (e.g. low to high latitude) progression,
shared across many species;
2 while generally losing territory, the species may in
fact expand into new territory outside the historical
range margin at the favoured range margin (Figure
7.3 ).
Latitudinal changes in the distributions of many
species have now been demonstrated, with some
groups exhibiting dramatic poleward range shifts
within historical time periods (Parmesan, 1996 ;
Hickling et al. , 2006 ). Studying the winter distributions of 254 bird species in North America, La Sorte &
Thompson (2007) found that the position of the
northern geographical range boundary, the centre of
occurrence and the centre of abundance all increased
on average during the time course of the study (1975 –
2004). In a fascinating review of palaeoecological
data, Arndt & R é my (2005) , highlight the importance
of considering the conservation needs of relictual populations left at the trailing edge as geographical ranges
shift with climate change.
As well as latitudinal shifts, there is also accumulating evidence of upward elevational shifts in species ’
distributions over recent history. Bryophytes respond
strongly to local climatic conditions and are well
adapted to colonize new locations if conditions become
suitable. This makes them an ideal group within which
to study responses to climate change.
Recent work in Switzerland has shown that the
mean elevational range and the position of the upper
elevational limit of cryophilous (cold - tolerant) bryophytes both increased signifi cantly between 1880 and
1920 and between 1980 and 2005 (Bergamini et al. ,
2009 ). The position of the lower elevational limit of
cryophilous species and the elevational range of less
cold - tolerant species was unchanged, consistent with
the shift being a result of climate change.
Another example comes from a study of the elevational distribution of breeding birds in the Italian Alps
by Popy et al . (2010) . They used data from two recent
atlas surveys (1 km grid squares) at an 11 - year interval
(1992 – 1994 and 2003 – 2005). As anticipated, they
Planning for persistence in a changing world
detected small increases in the mean elevation for the
majority of species but, because some species showed
downward shifts, the average change across all species
was not signifi cantly different from zero. They also
recorded a small change in species composition, which
corresponded on average to a 29 m upward elevational
shift in the distribution of the avifauna. The relatively
small shift in elevation is surprising, given the considerable increase in temperature in the region ( ≈ 1 ° C),
which suggest that elevational shifts in regions of
complex topography may not always have a simple
relationship with increasing regional temperatures.
Understanding the temporal patterns of geographical range collapses is also critical for designing conservation interventions. Species with small and declining
distributions are at especially high risk of extinction,
and this observation has been used by the conservation
community to prioritize species based on their short -
term probability of extinction (Mace & Collar, 1995 ;
IUCN, 2001 ). The distributions of species change naturally over evolutionary time, with range sizes broadly
increasing following speciation and then, subsequently,
declining towards extinction (Figure 7.1 ; Gaston,
2003 ; Vrba & DeGusta, 2004 ), but human intervention dramatically steepens the trajectory of decline
towards extinction, and conservation activity is often
focused on those species in which the rate of change is
particularly great.
However, sometimes the fi nal trajectory to extinction may be so steep that it is too late for effective conservation action. Furthermore, applying conservation
effort only in the fi nal stages of a species ’ decline may
lead to a continuous cycle of ‘ crisis management ’
(Linklater, 2003 ) and may be an ineffi cient use of
resources (Bottrill et al. , 2008 ).
7.3 PREDICTING BIODIVERSITY
CHANGE
The foregoing discussion has revealed many examples
of long - term changes in species ’ distributions, and
these are likely to accelerate in the future as humans
increasingly dominate the ecology of the planet. As
environmental conditions change over time, species
could:
1 move to locations where their preferred conditions
are still found;
2 adapt in some way to the changing conditions; or
trailing - edge populations expand in their population
size and supply colonists for range expansion so that
they are no longer absolutely the periphery of the
species range.
In such a scenario, the pattern will follow a similar
geographical pattern to the contagion hypothesis, but
with two key modifi cations:
1 the pattern of range collapse will follow a climatically predictable (e.g. low to high latitude) progression,
shared across many species;
2 while generally losing territory, the species may in
fact expand into new territory outside the historical
range margin at the favoured range margin (Figure
7.3 ).
Latitudinal changes in the distributions of many
species have now been demonstrated, with some
groups exhibiting dramatic poleward range shifts
within historical time periods (Parmesan, 1996 ;
Hickling et al. , 2006 ). Studying the winter distributions of 254 bird species in North America, La Sorte &
Thompson (2007) found that the position of the
northern geographical range boundary, the centre of
occurrence and the centre of abundance all increased
on average during the time course of the study (1975 –
2004). In a fascinating review of palaeoecological
data, Arndt & R é my (2005) , highlight the importance
of considering the conservation needs of relictual populations left at the trailing edge as geographical ranges
shift with climate change.
As well as latitudinal shifts, there is also accumulating evidence of upward elevational shifts in species ’
distributions over recent history. Bryophytes respond
strongly to local climatic conditions and are well
adapted to colonize new locations if conditions become
suitable. This makes them an ideal group within which
to study responses to climate change.
Recent work in Switzerland has shown that the
mean elevational range and the position of the upper
elevational limit of cryophilous (cold - tolerant) bryophytes both increased signifi cantly between 1880 and
1920 and between 1980 and 2005 (Bergamini et al. ,
2009 ). The position of the lower elevational limit of
cryophilous species and the elevational range of less
cold - tolerant species was unchanged, consistent with
the shift being a result of climate change.
Another example comes from a study of the elevational distribution of breeding birds in the Italian Alps
by Popy et al . (2010) . They used data from two recent
atlas surveys (1 km grid squares) at an 11 - year interval
(1992 – 1994 and 2003 – 2005). As anticipated, they