8
The roots of conservation biogeography
Box 1.2 Key d iversity and s cale c oncepts
The fi rst of the tables below is adapted from Whittaker et al . (2001) and highlights the varied meanings of the term species diversity, which itself is just one meaning of the term ‘ biodiversity ’ (see Box
1.1 ). Although the table refers to species as the unit of analysis, the terms can of course be applied
at other taxonomic levels. The terms given here have been used in varied and inconsistent ways in
the literature, leading to much confusion within diversity theory.
Within species diversity terminology, perhaps the key distinction is between metrics and concepts
recognizing differences in the number of species (which are forms of inventory diversity) and those
that highlight the degree to which species are shared between or unique to (endemic to) the areas
being compared (which are forms of differentiation diversity). This distinction is set out in Table B1.2b ,
which provides the foundational framework for the scale of application, designated by letters of the
Greek alphabet, developed by the American ecologist Robert Harding Whittaker (e.g. 1960 , 1977 ).
R.H. Whittaker ’ s framework provided a nested sequence from inventory to differentiation forms
reiteratively (Figure B1.2a ). As his fi rst inventory tier was termed alpha diversity and his fi rst differentiation tier was termed beta diversity, he sometimes used the two terms interchangeably, a habit
followed by many other authors, sometimes with confusing outcomes. In practice, diversity and
other biogeographical patterns described at different focal scales of analysis may well be the
outcome of different dominant processes, so it is of critical importance that the scale parameters
of a study are explicitly taken into account when synthesizing information within biogeography, not
least within conservation biogeography (see discussion in Whittaker et al ., 2001 , 2005 ).
Table B1.2a Key diversity and scale concepts. Modifi ed from Whittaker et al. ( 2001 , Table 1).
Diversity concepts Meaning
species diversity
varied meaning: e.g. number of species, or indices weighted by abundance
distributions of species (equitability); implying of itself no standardization of sampling
species richness
number of species, implying of itself no standardization of sampling
species density
number of species in a standardized sample, e.g. per unit area; more precise than the
above but less widely adopted
species turnover, i.e.
differentiation
diversity
in the present context meaning compositional turnover in space between two inventory
(typically alpha - scale) samples, expressed by a variety of indices or multivariate
analyses, and thus qualitatively different from species richness or density
endemism
an endemic is simply a species (or other taxonomic entity) confi ned to a particular
geographical area; a focus on areas of high numbers of endemics implies an interest
in biogeographical distinctiveness (whether at species or other taxonomic level)
Scale concepts
Meaning
spatial scale
should refer to the size of the base unit used in sampling and analysis, but in practice
usage of this term varies such that it may mean either or both of ‘ extent ’ and ‘ focus ’ ;
moreover, size of sample unit is very often not held a constant (as it should be) but is
allowed to vary within a study
(geographical)
extent
the geographical space (distance) over which comparisons are made, whether they be
using e.g. 1 m
2 or 10,000 km
2 sample units; i.e. of itself implying nothing about spatial
scale in the strict sense
focal scale
the spatial scale at which data are analysed, being either the size of the sampling unit
(also called the ‘ grain ’ ) or the unit to which these data are aggregated for analysis
(e.g. local or fi eld scale to regional scale); this concept, unlike ‘ extent ’ , can be
synonymous with spatial scale
The roots of conservation biogeography
Box 1.2 Key d iversity and s cale c oncepts
The fi rst of the tables below is adapted from Whittaker et al . (2001) and highlights the varied meanings of the term species diversity, which itself is just one meaning of the term ‘ biodiversity ’ (see Box
1.1 ). Although the table refers to species as the unit of analysis, the terms can of course be applied
at other taxonomic levels. The terms given here have been used in varied and inconsistent ways in
the literature, leading to much confusion within diversity theory.
Within species diversity terminology, perhaps the key distinction is between metrics and concepts
recognizing differences in the number of species (which are forms of inventory diversity) and those
that highlight the degree to which species are shared between or unique to (endemic to) the areas
being compared (which are forms of differentiation diversity). This distinction is set out in Table B1.2b ,
which provides the foundational framework for the scale of application, designated by letters of the
Greek alphabet, developed by the American ecologist Robert Harding Whittaker (e.g. 1960 , 1977 ).
R.H. Whittaker ’ s framework provided a nested sequence from inventory to differentiation forms
reiteratively (Figure B1.2a ). As his fi rst inventory tier was termed alpha diversity and his fi rst differentiation tier was termed beta diversity, he sometimes used the two terms interchangeably, a habit
followed by many other authors, sometimes with confusing outcomes. In practice, diversity and
other biogeographical patterns described at different focal scales of analysis may well be the
outcome of different dominant processes, so it is of critical importance that the scale parameters
of a study are explicitly taken into account when synthesizing information within biogeography, not
least within conservation biogeography (see discussion in Whittaker et al ., 2001 , 2005 ).
Table B1.2a Key diversity and scale concepts. Modifi ed from Whittaker et al. ( 2001 , Table 1).
Diversity concepts Meaning
species diversity
varied meaning: e.g. number of species, or indices weighted by abundance
distributions of species (equitability); implying of itself no standardization of sampling
species richness
number of species, implying of itself no standardization of sampling
species density
number of species in a standardized sample, e.g. per unit area; more precise than the
above but less widely adopted
species turnover, i.e.
differentiation
diversity
in the present context meaning compositional turnover in space between two inventory
(typically alpha - scale) samples, expressed by a variety of indices or multivariate
analyses, and thus qualitatively different from species richness or density
endemism
an endemic is simply a species (or other taxonomic entity) confi ned to a particular
geographical area; a focus on areas of high numbers of endemics implies an interest
in biogeographical distinctiveness (whether at species or other taxonomic level)
Scale concepts
Meaning
spatial scale
should refer to the size of the base unit used in sampling and analysis, but in practice
usage of this term varies such that it may mean either or both of ‘ extent ’ and ‘ focus ’ ;
moreover, size of sample unit is very often not held a constant (as it should be) but is
allowed to vary within a study
(geographical)
extent
the geographical space (distance) over which comparisons are made, whether they be
using e.g. 1 m
2 or 10,000 km
2 sample units; i.e. of itself implying nothing about spatial
scale in the strict sense
focal scale
the spatial scale at which data are analysed, being either the size of the sampling unit
(also called the ‘ grain ’ ) or the unit to which these data are aggregated for analysis
(e.g. local or fi eld scale to regional scale); this concept, unlike ‘ extent ’ , can be
synonymous with spatial scale