166
Planning for persistence in a changing world
Box 7.1 Integrating e volutionary c onsiderations into c onservation p lanning
Species have traditionally been used as the primary taxonomic level for conservation and, as we
have seen, many conservation prioritization analyses essentially rely on weighing up tallies of rare,
threatened, or range - restricted species. This strategy has the advantage of needing little or no
explanation for policymakers or the public.
However, even within a single taxonomic group such as plants or mammals, such a focus may
result in some highly valued species or assemblages being omitted from conservation prioritization
because they happen not to fall in the most diverse areas. One aspect of the way in which we may
value species is in terms of their evolutionary distinctiveness, and here the question arises as to
whether a strategy focused on maximizing species richness of a taxon will also succeed in capturing
a broad representation of the evolutionary tree, thus preserving the phylogenetic diversity and future
evolutionary potential of that group.
Phylogenetic diversity (PD) can be defi ned as a biodiversity index that measures the length of
evolutionary pathways that connect a given set of taxa, and it is regarded as a surrogate for the
‘ feature diversity ’ that arises along the branches of the evolutionary tree (Faith, 2006 ; Forest et al. ,
2007 ). Quantifying the diversity of such ‘ features ’ is important because it is diffi cult to know which
features of an organism will be advantageous as the environment changes. Thus, maximizing PD
may be the best bet - hedging strategy to ensure that evolution has the necessary raw materials on
which to work in a rapidly changing world.
The potential application of phylogenetic diversity within conservation planning is illustrated by a
recent study by Forest et al . (2007) on the remarkable fl ora of the Cape region of South Africa – an
undisputed biodiversity hotspot containing more than 9,000 plant species, a staggering 70 per cent
of which are endemic. They collected and compiled distribution data for the entire Cape and created
an inventory of species and genera per quarter - degree square. They also reconstructed the phylogeny (phylogenetic tree) of the Cape fl ora based on analysis of plastids from 735 genera, each
indigenous to the Cape.
The results were fascinating, if somewhat complex. PD and species (or genus) richness were
broadly correlated (areas of high PD also had high richness), suggesting that traditional conservation
planning strategies of maximizing species richness may be equally effective at maintaining PD.
However, as is often the case, the devil is in the detail. PD was found to scale with richness in a
complex manner, so that some regions had more or less PD than would be expected from their
species richness. Forest et al . (2007) uncovered a distinctive east/west division in the distribution
of PD that broadly corresponded to climatic zones in the Cape region. Specifi cally, PD for a given
number of taxa was higher in the eastern region than in the west (Figure B7.1a ).
The consequences of such a geographical decoupling of PD and taxon richness is that, in the
event of extinctions of non - prioritized species, a traditional taxon (species or genus) richness
approach to conservation planning might lose disproportionate numbers of species possessing
unique evolutionary characteristics. This, in turn, would reduce the evolutionary potential to respond,
adapt and diversify in the light of changes in climate, land use, species composition, etc.
Whether such PD approaches will become widespread in conservation planning is debatable. As
the authors themselves note, taxon diversity will remain an important conservation target, and it is
by no means straightforward to balance prioritizations based on these two indices. Moreover, there
is a serious scale issue that may be largely intractable: any conservation plan that operates at less
than a global scale runs the risk of fi nding solutions that are optimal only within the study region.
Using distinct phylogeographical regions such as the Cape region reduces, but does not totally
resolve, this issue.
Planning for persistence in a changing world
Box 7.1 Integrating e volutionary c onsiderations into c onservation p lanning
Species have traditionally been used as the primary taxonomic level for conservation and, as we
have seen, many conservation prioritization analyses essentially rely on weighing up tallies of rare,
threatened, or range - restricted species. This strategy has the advantage of needing little or no
explanation for policymakers or the public.
However, even within a single taxonomic group such as plants or mammals, such a focus may
result in some highly valued species or assemblages being omitted from conservation prioritization
because they happen not to fall in the most diverse areas. One aspect of the way in which we may
value species is in terms of their evolutionary distinctiveness, and here the question arises as to
whether a strategy focused on maximizing species richness of a taxon will also succeed in capturing
a broad representation of the evolutionary tree, thus preserving the phylogenetic diversity and future
evolutionary potential of that group.
Phylogenetic diversity (PD) can be defi ned as a biodiversity index that measures the length of
evolutionary pathways that connect a given set of taxa, and it is regarded as a surrogate for the
‘ feature diversity ’ that arises along the branches of the evolutionary tree (Faith, 2006 ; Forest et al. ,
2007 ). Quantifying the diversity of such ‘ features ’ is important because it is diffi cult to know which
features of an organism will be advantageous as the environment changes. Thus, maximizing PD
may be the best bet - hedging strategy to ensure that evolution has the necessary raw materials on
which to work in a rapidly changing world.
The potential application of phylogenetic diversity within conservation planning is illustrated by a
recent study by Forest et al . (2007) on the remarkable fl ora of the Cape region of South Africa – an
undisputed biodiversity hotspot containing more than 9,000 plant species, a staggering 70 per cent
of which are endemic. They collected and compiled distribution data for the entire Cape and created
an inventory of species and genera per quarter - degree square. They also reconstructed the phylogeny (phylogenetic tree) of the Cape fl ora based on analysis of plastids from 735 genera, each
indigenous to the Cape.
The results were fascinating, if somewhat complex. PD and species (or genus) richness were
broadly correlated (areas of high PD also had high richness), suggesting that traditional conservation
planning strategies of maximizing species richness may be equally effective at maintaining PD.
However, as is often the case, the devil is in the detail. PD was found to scale with richness in a
complex manner, so that some regions had more or less PD than would be expected from their
species richness. Forest et al . (2007) uncovered a distinctive east/west division in the distribution
of PD that broadly corresponded to climatic zones in the Cape region. Specifi cally, PD for a given
number of taxa was higher in the eastern region than in the west (Figure B7.1a ).
The consequences of such a geographical decoupling of PD and taxon richness is that, in the
event of extinctions of non - prioritized species, a traditional taxon (species or genus) richness
approach to conservation planning might lose disproportionate numbers of species possessing
unique evolutionary characteristics. This, in turn, would reduce the evolutionary potential to respond,
adapt and diversify in the light of changes in climate, land use, species composition, etc.
Whether such PD approaches will become widespread in conservation planning is debatable. As
the authors themselves note, taxon diversity will remain an important conservation target, and it is
by no means straightforward to balance prioritizations based on these two indices. Moreover, there
is a serious scale issue that may be largely intractable: any conservation plan that operates at less
than a global scale runs the risk of fi nding solutions that are optimal only within the study region.
Using distinct phylogeographical regions such as the Cape region reduces, but does not totally
resolve, this issue.