Conservation planning in a changing world
241
unique species over time, and neither complementarity
nor the level of biotic homogenization would change,
yet the true state of biodiversity loss will not be refl ected.
9.6 NOVEL ASSEMBLAGES
Novel assemblages, sometimes referred to as novel or
emerging ecosystems, are communities that consist of
extant species which have not occurred previously in
the same combinations found today (Hobbs et al. ,
2006 ). Increased homogenization of biotas associated
with the massive and accelerating movement of species
within and between regions/provinces is likely to contribute substantially to the creation of novel or no -
analogue assemblages.
Although, technically, any area that has lost native
species or gained non - native species is novel in some
respect, some current assemblages have been transformed to such an extent that they are verging on
becoming entirely new assemblages (Williams &
Jackson, 2007 ). Certainly, in terms of system functioning, many ecosystems have already become ‘ novel ’ .
One of the best examples comes from the San
Francisco Bay, California, which has the dubious distinction of being the most invaded aquatic region on
Earth, with more than half its fi sh and most of its
bottom - dwelling organisms representing non - native
species (Cohen & Carlton, 1998 ). The total dominance
(number of species and biomass) of non - native species
has transformed the bay from a pelagic (mid - water)
system to a benthic (bottom) one and productivity has
declined. Invasive species such as Corbula amurensis
(Asian clam), Sphaeroma quoyanum (a burrowing
isopod from Australia and New Zealand) and Spartina
alternifl ora (smooth cordgrass) have become among the
most important species in the bay in terms of both
biomass and their role in controlling biological processes in the bay (Cohen & Carlton, 1998 ).
Although the process of homogenization can create
novel assemblages, global climate change is increasingly likely to magnify this effect. Thus, any prediction
of where novel assemblages will form needs to take into
account not only non - native species introductions, but
also global climate change and the individualistic
responses of species (native and non - native) to environmental change (Chapters 4 , 7 ). Recent models
suggest there will be substantial regions of the world
with novel climates by 2100 (particularly in tropical
and sub - tropical regions) and also that some extant
This act is a problem when species are introduced
and become established outside of their historical distribution, or where the genetic consequences (e.g.
interspecifi c hybridization) are not considered. For
example, in parks across southern Africa there has
been a trend to introduce the same suite of species
across nature reserves. Fuelled by tourism and the public ’ s desire to see large mammals (especially predators),
spotted hyena ( Crocuta crocuta ), wild dog ( Lycaon pictus )
and antelope such as roan ( Hippotragus equinus ) have
been introduced and have established within areas
where they did not historically occur, or to areas that
are now unsuitable due to small park sizes.
In fact, Spear and Chown (2008) demonstrated that
it is extra - limital introductions that are driving the
homogenization of ungulate assemblages in South
Africa (Figure 9.6 ). They warn that the potential for
changes in local diversity and ecosystem functioning as
a consequence of translocations should not be underestimated. These concerns contrast with other conservation actors arguing for various forms of rewilding, or
for assisted migrations of species as a climate - change
mitigation strategy (see, e.g. Chapter 3 ; Donlan, 2007 ).
The concept of biotic homogenization and differentiation may provide a useful tool in conservation
planning (Rooney et al. , 2007 ). Much attention in conservation has focused on reserve selection and choosing the best network of reserves to maximize
biodiversity coverage. Such efforts have largely focused
on species number, endemism and complementarity as
the metrics that should be optimized (Chapters 6 and
7 ; Pressey et al. , 1993 ).
Complementarity exists when an area has some biodiversity components that are unrepresented in other
areas. It may thus be possible to use biotic homogenization to monitor whether complementarity goals are
being met. For example, if a network of reserves
becomes more similar over time due to the loss of
unique species, this reduces complementarity (Rooney
et al. , 2007 ).
Importantly, any assessment of complementarity
related to conservation planning should be restricted
to indigenous species only. The inclusion of non - native
species could show increased biotic homogenization
when, in reality, the full set of native species that the
reserve network was designed to conserve still occur.
This idea has much potential, but there are a few
caveats. For example, when dealing with a minimum
set complementarity (each area contains distinctive
species) goal, all areas may lose the same number of
241
unique species over time, and neither complementarity
nor the level of biotic homogenization would change,
yet the true state of biodiversity loss will not be refl ected.
9.6 NOVEL ASSEMBLAGES
Novel assemblages, sometimes referred to as novel or
emerging ecosystems, are communities that consist of
extant species which have not occurred previously in
the same combinations found today (Hobbs et al. ,
2006 ). Increased homogenization of biotas associated
with the massive and accelerating movement of species
within and between regions/provinces is likely to contribute substantially to the creation of novel or no -
analogue assemblages.
Although, technically, any area that has lost native
species or gained non - native species is novel in some
respect, some current assemblages have been transformed to such an extent that they are verging on
becoming entirely new assemblages (Williams &
Jackson, 2007 ). Certainly, in terms of system functioning, many ecosystems have already become ‘ novel ’ .
One of the best examples comes from the San
Francisco Bay, California, which has the dubious distinction of being the most invaded aquatic region on
Earth, with more than half its fi sh and most of its
bottom - dwelling organisms representing non - native
species (Cohen & Carlton, 1998 ). The total dominance
(number of species and biomass) of non - native species
has transformed the bay from a pelagic (mid - water)
system to a benthic (bottom) one and productivity has
declined. Invasive species such as Corbula amurensis
(Asian clam), Sphaeroma quoyanum (a burrowing
isopod from Australia and New Zealand) and Spartina
alternifl ora (smooth cordgrass) have become among the
most important species in the bay in terms of both
biomass and their role in controlling biological processes in the bay (Cohen & Carlton, 1998 ).
Although the process of homogenization can create
novel assemblages, global climate change is increasingly likely to magnify this effect. Thus, any prediction
of where novel assemblages will form needs to take into
account not only non - native species introductions, but
also global climate change and the individualistic
responses of species (native and non - native) to environmental change (Chapters 4 , 7 ). Recent models
suggest there will be substantial regions of the world
with novel climates by 2100 (particularly in tropical
and sub - tropical regions) and also that some extant
This act is a problem when species are introduced
and become established outside of their historical distribution, or where the genetic consequences (e.g.
interspecifi c hybridization) are not considered. For
example, in parks across southern Africa there has
been a trend to introduce the same suite of species
across nature reserves. Fuelled by tourism and the public ’ s desire to see large mammals (especially predators),
spotted hyena ( Crocuta crocuta ), wild dog ( Lycaon pictus )
and antelope such as roan ( Hippotragus equinus ) have
been introduced and have established within areas
where they did not historically occur, or to areas that
are now unsuitable due to small park sizes.
In fact, Spear and Chown (2008) demonstrated that
it is extra - limital introductions that are driving the
homogenization of ungulate assemblages in South
Africa (Figure 9.6 ). They warn that the potential for
changes in local diversity and ecosystem functioning as
a consequence of translocations should not be underestimated. These concerns contrast with other conservation actors arguing for various forms of rewilding, or
for assisted migrations of species as a climate - change
mitigation strategy (see, e.g. Chapter 3 ; Donlan, 2007 ).
The concept of biotic homogenization and differentiation may provide a useful tool in conservation
planning (Rooney et al. , 2007 ). Much attention in conservation has focused on reserve selection and choosing the best network of reserves to maximize
biodiversity coverage. Such efforts have largely focused
on species number, endemism and complementarity as
the metrics that should be optimized (Chapters 6 and
7 ; Pressey et al. , 1993 ).
Complementarity exists when an area has some biodiversity components that are unrepresented in other
areas. It may thus be possible to use biotic homogenization to monitor whether complementarity goals are
being met. For example, if a network of reserves
becomes more similar over time due to the loss of
unique species, this reduces complementarity (Rooney
et al. , 2007 ).
Importantly, any assessment of complementarity
related to conservation planning should be restricted
to indigenous species only. The inclusion of non - native
species could show increased biotic homogenization
when, in reality, the full set of native species that the
reserve network was designed to conserve still occur.
This idea has much potential, but there are a few
caveats. For example, when dealing with a minimum
set complementarity (each area contains distinctive
species) goal, all areas may lose the same number of