The distribution of diversity: challenges and applications
65
The most promising aspect of DNA barcoding is that
it represents a true union between the goals of systematists, biogeographers, ecologists and an array of
other constituencies, including public health organizations. For purposes of conservation biogeography, DNA
barcoding will likely have its greatest impact by fi lling
in some of the details of species diversity in lesser -
known and morphologically cryptic taxa, and of the
distributions of taxa, thereby reducing the magnitude
of both Linnean and Wallacean shortfalls.
4.4 SPATIAL DISTRIBUTIONS: FROM
GENES TO BIOGEOGRAPHICAL
REGIONS
4.4.1 Mapping s pecies i ndividually
and c ollectively
The distributions of species are often represented by
what are sometimes termed range - fi lling maps, i.e.
coarsely drawn envelopes encompassing the known
outer limits of the species ’ distribution, within which
ranges are represented as solid entities. In poorly surveyed areas of the world, such maps may involve
extrapolations based on general knowledge of the
habitat in which the species is known to be found.
These maps do not provide a sound basis for conservation planning purposes.
The generally recognized protocol for mapping
species, however, is to use some form of grid - cell
system, preferably using equal areas and typically
using grid cells of 10 × 10 or 50 × 50 km or 0.5
degrees (latitude/longitude). The species is recognized
as present in the cell only when established to be
present by direct observation, ideally backed by voucher
specimens collected and stored in herbaria/museums.
When species ranges are mapped in this way, it becomes
evident that species ’ distributions are discontinuous
(as exemplifi ed in Figures 4.2 and 4.4 ). This may be
more apparent for some taxa than for others, but it
actually applies to all species if distributions are
recorded and mapped on a fi ne enough scale of analysis, although some highly endangered species have
such small ranges that they may be considered to
consist of a single population and provide a single dot
on the map.
Given that environments are patchy, it is, of course,
unremarkable that species ’ distributions should also be
patchy. So, for example, in the UK a plant adapted to
Moritz (1994) also recognized that his defi nition of
ESU may well be too stringent to allow the recognition
of some important variation and, for this reason, also
proposed a lower level for conservation application,
known as the Management Unit (MU). Management
units are populations which may not show reciprocal
monophyly for mtDNA alleles (and by extension, presumably cpDNA in plants), yet which have diverged
in allele frequencies at nuclear or organelle DNA loci
and are therefore worthy of some level of monitoring
or protection. MUs are signifi cant for conservation
in that they represent populations connected by such
low levels of gene fl ow that they are functionally
independent.
4.3.3 Other c onservation u nits
One of the latest additions to the units of conservation
debate is the suggestion that for large, complex animals
such as mammals and birds, conservationists should
try to identify culturally distinct population segments,
especially if the populations are small or endangered.
Such Culturally Signifi cant Units (CSUs) could be vital
to future survival if the behaviour confers a distinct
adaptive advantage or confers greater adaptability on
the population (Ryan, 2006 ). A good example is the
different cultures of tool use seen in wild populations
of chimpanzees ( Pan troglodytes ) in west Africa (Whiten
& Boesch, 2001 ). CSUs are the cultural equivalent of
ESUs, in that they also require some form of population
isolation although, in contrast to ESUs, signifi cant
levels of genetic divergence are not implied.
Finally, yet another tool conceptually affi liated to the
PSC and phylogeography, and which may speed up
identifi cation of new ‘ species ’ , is DNA barcoding: the
use of short, unique sections of the genetic profi le of a
species sample for the purposes of identifi cation, rather
like the barcode on your groceries (Hebert et al ., 2003 ).
DNA barcoding relies on sequencing a standardized
segment of DNA – originally and still most often a
portion of the mitochondrial cytochrome c oxidase
subunit 1 (COI) in animals and plants, or the nuclear
ribosomal internal transcribed spacer region (ITS) in
fungi – and comparing that sequence against a database of many thousands of homologous (see Glossary)
sequences to determine if it represents a previously
unknown species or one that is already registered in
the database ( http://barcoding.si.edu/; http://www.
boldsystems.org ).
65
The most promising aspect of DNA barcoding is that
it represents a true union between the goals of systematists, biogeographers, ecologists and an array of
other constituencies, including public health organizations. For purposes of conservation biogeography, DNA
barcoding will likely have its greatest impact by fi lling
in some of the details of species diversity in lesser -
known and morphologically cryptic taxa, and of the
distributions of taxa, thereby reducing the magnitude
of both Linnean and Wallacean shortfalls.
4.4 SPATIAL DISTRIBUTIONS: FROM
GENES TO BIOGEOGRAPHICAL
REGIONS
4.4.1 Mapping s pecies i ndividually
and c ollectively
The distributions of species are often represented by
what are sometimes termed range - fi lling maps, i.e.
coarsely drawn envelopes encompassing the known
outer limits of the species ’ distribution, within which
ranges are represented as solid entities. In poorly surveyed areas of the world, such maps may involve
extrapolations based on general knowledge of the
habitat in which the species is known to be found.
These maps do not provide a sound basis for conservation planning purposes.
The generally recognized protocol for mapping
species, however, is to use some form of grid - cell
system, preferably using equal areas and typically
using grid cells of 10 × 10 or 50 × 50 km or 0.5
degrees (latitude/longitude). The species is recognized
as present in the cell only when established to be
present by direct observation, ideally backed by voucher
specimens collected and stored in herbaria/museums.
When species ranges are mapped in this way, it becomes
evident that species ’ distributions are discontinuous
(as exemplifi ed in Figures 4.2 and 4.4 ). This may be
more apparent for some taxa than for others, but it
actually applies to all species if distributions are
recorded and mapped on a fi ne enough scale of analysis, although some highly endangered species have
such small ranges that they may be considered to
consist of a single population and provide a single dot
on the map.
Given that environments are patchy, it is, of course,
unremarkable that species ’ distributions should also be
patchy. So, for example, in the UK a plant adapted to
Moritz (1994) also recognized that his defi nition of
ESU may well be too stringent to allow the recognition
of some important variation and, for this reason, also
proposed a lower level for conservation application,
known as the Management Unit (MU). Management
units are populations which may not show reciprocal
monophyly for mtDNA alleles (and by extension, presumably cpDNA in plants), yet which have diverged
in allele frequencies at nuclear or organelle DNA loci
and are therefore worthy of some level of monitoring
or protection. MUs are signifi cant for conservation
in that they represent populations connected by such
low levels of gene fl ow that they are functionally
independent.
4.3.3 Other c onservation u nits
One of the latest additions to the units of conservation
debate is the suggestion that for large, complex animals
such as mammals and birds, conservationists should
try to identify culturally distinct population segments,
especially if the populations are small or endangered.
Such Culturally Signifi cant Units (CSUs) could be vital
to future survival if the behaviour confers a distinct
adaptive advantage or confers greater adaptability on
the population (Ryan, 2006 ). A good example is the
different cultures of tool use seen in wild populations
of chimpanzees ( Pan troglodytes ) in west Africa (Whiten
& Boesch, 2001 ). CSUs are the cultural equivalent of
ESUs, in that they also require some form of population
isolation although, in contrast to ESUs, signifi cant
levels of genetic divergence are not implied.
Finally, yet another tool conceptually affi liated to the
PSC and phylogeography, and which may speed up
identifi cation of new ‘ species ’ , is DNA barcoding: the
use of short, unique sections of the genetic profi le of a
species sample for the purposes of identifi cation, rather
like the barcode on your groceries (Hebert et al ., 2003 ).
DNA barcoding relies on sequencing a standardized
segment of DNA – originally and still most often a
portion of the mitochondrial cytochrome c oxidase
subunit 1 (COI) in animals and plants, or the nuclear
ribosomal internal transcribed spacer region (ITS) in
fungi – and comparing that sequence against a database of many thousands of homologous (see Glossary)
sequences to determine if it represents a previously
unknown species or one that is already registered in
the database ( http://barcoding.si.edu/; http://www.
boldsystems.org ).