Conservation planning in a changing world
169
Nogu é s - Bravo et al . (2008) used a combination of
climate envelope models and population models to
demonstrate that the woolly mammoth ( Mammuthus
primigenius ) probably declined rapidly owing to a dwindling of the area of suitable climate space, fi nally reaching a point at which the reduced populations became
vulnerable to increasing human hunting pressure.
Along with the arrival of mechanized agriculture,
stories abound of rapid extinctions of formerly common
or widespread species, many of which have resulted
from human intervention (Gaston & Fuller, 2007 ).
Rocky Mountain grasshoppers ( Melanoplus spretus )
were once distributed across much of the western USA,
numbering perhaps 15 trillion individuals in outbreak
years. They destroyed crops over vast areas and devastated plains farming communities in the mid 19th
century. During non - outbreak years, they were
restricted to valley bottoms in the Rocky Mountains –
favoured areas for a rapidly expanding agriculture. In
the closing decades of the 19th century, localized
habitat destruction in these areas triggered a precipitous decline to extinction (Lockwood & DeBrey, 1990 ).
Despite the focus in much of the literature about
declines, lessons from history are not always about
reductions and losses. There are also examples of
dramatic gains in species ’ distributions. For example,
the slow transition from the ice sheets of the Last
Glacial Maximum (about 16,000 years ago) to forests
and farmland was accompanied by dramatic responses
in faunal densities and community structure and
composition. Hence, for example, the total number of
wild mammals in Britain has been estimated to have
been as high as around 535 million about 7,000 years
ago (Maroo & Yalden, 2000 ). Some species have
declined precipitously since this period as forests have
been converted for agriculture, yet populations of
some other species have increased as they benefi ted
from the opening up of habitats (Table 7.1 ). The fi ve
species with highest estimated abundance during the
Mesolithic accounted for 80 per cent of the loss of individuals in comparison with the present - day fauna.
Combined with eight extinctions over the time period,
these changes have resulted in markedly different
mammalian communities in the country within a few
thousand years.
Many farmland bird species in the UK have followed
similar trajectories of expansion and decline as
forest has been converted to agricultural lands and
agricultural use has then progressively intensifi ed.
For example, grey partridge ( Perdix perdix ) numbers
Inference about process based on correlational
pattern - based study alone can be misleading, however.
For example, reef corals in the Caribbean that appear
to have been stable for at least 125,000 years suddenly
collapsed in a mass mortality event in the 1980s
(Jackson, 1992 ). One of the important proximate
events leading to this collapse was the widespread
disease - induced mortality of the grazing sea urchin
Diadema antillarum , allowing macroalgae to overgrow
and choke the corals.
Most contemporary ecological investigation would
have concluded there. However, careful analysis of palaeoecological, archaeological and historical data
showed that fi shing activity between the 17th and
19th centuries had decimated populations of large
consumers such as marine turtles, large fi sh, sharks
and manatees (Jackson et al. , 2001 ). The loss of these
large species greatly simplifi ed the community, leading
to the dominance of niche space by one species of
grazing sea urchin. The superabundance of the urchin
created good conditions for disease spread and reduced
the redundancy in the system, leading to a rapid collapse (Jackson, 2001 ).
More generally, historical overfi shing, the impacts of
which are now not readily observable directly, pre - date
modern anthropogenic impacts such as climate
change, introduced species and the spread of diseases,
which are the factors often implicated in biodiversity
loss.
7.2.2 Interpreting r ecent t rends in t heir
h istorical c ontext
A second key contribution of long - term ecology to conservation is founded on the recognition that the patterns we see today can only be interpreted in their
long - term context. Declines in species ’ abundances or
geographical ranges, insofar as they predict extinction
probability, are routinely used to prioritize species for
conservation action. However, an understanding of
natural variability in population size is crucial in interpreting any particular observed decline, and historical
records have been used on many occasions to place
current declines in context.
Many early human impacts (e.g. forest clearance,
changes in fi re regimes) have been higher in severity
and commenced much earlier than previously realized
and, sometimes, anthropogenic impacts have compounded natural reasons for declines. For example,
169
Nogu é s - Bravo et al . (2008) used a combination of
climate envelope models and population models to
demonstrate that the woolly mammoth ( Mammuthus
primigenius ) probably declined rapidly owing to a dwindling of the area of suitable climate space, fi nally reaching a point at which the reduced populations became
vulnerable to increasing human hunting pressure.
Along with the arrival of mechanized agriculture,
stories abound of rapid extinctions of formerly common
or widespread species, many of which have resulted
from human intervention (Gaston & Fuller, 2007 ).
Rocky Mountain grasshoppers ( Melanoplus spretus )
were once distributed across much of the western USA,
numbering perhaps 15 trillion individuals in outbreak
years. They destroyed crops over vast areas and devastated plains farming communities in the mid 19th
century. During non - outbreak years, they were
restricted to valley bottoms in the Rocky Mountains –
favoured areas for a rapidly expanding agriculture. In
the closing decades of the 19th century, localized
habitat destruction in these areas triggered a precipitous decline to extinction (Lockwood & DeBrey, 1990 ).
Despite the focus in much of the literature about
declines, lessons from history are not always about
reductions and losses. There are also examples of
dramatic gains in species ’ distributions. For example,
the slow transition from the ice sheets of the Last
Glacial Maximum (about 16,000 years ago) to forests
and farmland was accompanied by dramatic responses
in faunal densities and community structure and
composition. Hence, for example, the total number of
wild mammals in Britain has been estimated to have
been as high as around 535 million about 7,000 years
ago (Maroo & Yalden, 2000 ). Some species have
declined precipitously since this period as forests have
been converted for agriculture, yet populations of
some other species have increased as they benefi ted
from the opening up of habitats (Table 7.1 ). The fi ve
species with highest estimated abundance during the
Mesolithic accounted for 80 per cent of the loss of individuals in comparison with the present - day fauna.
Combined with eight extinctions over the time period,
these changes have resulted in markedly different
mammalian communities in the country within a few
thousand years.
Many farmland bird species in the UK have followed
similar trajectories of expansion and decline as
forest has been converted to agricultural lands and
agricultural use has then progressively intensifi ed.
For example, grey partridge ( Perdix perdix ) numbers
Inference about process based on correlational
pattern - based study alone can be misleading, however.
For example, reef corals in the Caribbean that appear
to have been stable for at least 125,000 years suddenly
collapsed in a mass mortality event in the 1980s
(Jackson, 1992 ). One of the important proximate
events leading to this collapse was the widespread
disease - induced mortality of the grazing sea urchin
Diadema antillarum , allowing macroalgae to overgrow
and choke the corals.
Most contemporary ecological investigation would
have concluded there. However, careful analysis of palaeoecological, archaeological and historical data
showed that fi shing activity between the 17th and
19th centuries had decimated populations of large
consumers such as marine turtles, large fi sh, sharks
and manatees (Jackson et al. , 2001 ). The loss of these
large species greatly simplifi ed the community, leading
to the dominance of niche space by one species of
grazing sea urchin. The superabundance of the urchin
created good conditions for disease spread and reduced
the redundancy in the system, leading to a rapid collapse (Jackson, 2001 ).
More generally, historical overfi shing, the impacts of
which are now not readily observable directly, pre - date
modern anthropogenic impacts such as climate
change, introduced species and the spread of diseases,
which are the factors often implicated in biodiversity
loss.
7.2.2 Interpreting r ecent t rends in t heir
h istorical c ontext
A second key contribution of long - term ecology to conservation is founded on the recognition that the patterns we see today can only be interpreted in their
long - term context. Declines in species ’ abundances or
geographical ranges, insofar as they predict extinction
probability, are routinely used to prioritize species for
conservation action. However, an understanding of
natural variability in population size is crucial in interpreting any particular observed decline, and historical
records have been used on many occasions to place
current declines in context.
Many early human impacts (e.g. forest clearance,
changes in fi re regimes) have been higher in severity
and commenced much earlier than previously realized
and, sometimes, anthropogenic impacts have compounded natural reasons for declines. For example,