27
sums the branch lengths among species within a community (from the root of the
phylogeny to the tip). One feature of this metric is that it scales with species richness
because as new species are added into the community, new branch lengths are also
added. Other metrics were subsequently developed that calculate the mean evolutionary distances among species independently of the number of species [e.g., mean phylogenetic distance (MPD, Webb 2000b; Webb et al. 2002) or phylogenetic species
variability (PSV), Helmus 2007]. Helmus (2007) developed two more phylogenetic
diversity metrics that scale either with richness or by incorporating species abundances. Phylogenetic species richness (PSR) increases with the number of species, but
reduces the effect of species richness proportionally to their degree of shared ancestry.
Phylogenetic species evenness (PSE) is similar to PSV but includes abundances by
adding individuals as additional tips descending from a single species node, with
branch lengths of 0. Chao et al. (2010) defined the phylogenetic Hill number,
q
D(T),
as the effective number of equally abundant and equally distinct lineages and phylogenetic branch diversity,
q
PD(T), as the effective total lineage length from the root
node (i.e., the total evolutionary history of an assemblage) (Chao et al. 2014).
Phylogenetic endemism is another aspect of biodiversity that can be estimated
from phylogenetic information and range maps of species (Faith et al. 2004).
Phylogenetic endemism can be simply defined as the quantity of PD restricted to a
given geographic area. This metric thus focuses on geographic areas, rather than on
species, to discern areas of high endemism based on evolutionary history for conservation purposes.
2.7.4 Functional Diversity
Widely used metrics of functional diversity consider the area or volume of trait
space occupied by a community of species, the distances of each species to the center of gravity of those traits, and the trait distances between species (Mouillot et al.
2013). Functional attribute diversity (FAD) is a simple multivariate metric calculated as the sum of species pairwise distances of all measured continuous functional
traits (Walker et al. 1999). Villeger et al. (2008) developed a series of functional
diversity metrics that incorporate trait dispersion and distance among species as
well as species abundances, including functional richness (FRic), functional divergence (FDiv), and functional evenness (FEve). Building on the framework of
Villeger et al. (2008), Laliberté and Legendre (2010) developed functional dispersion
(FDis), a functional diversity metric that is independent of species richness and can
include species relative abundances (Table 2.1).
Scheiner’s functional trait dispersion [
q
D(TM), Scheiner et al. 2017] calculates
the effective number of species (or units) that are as distinct as the most distinct species (or unit) in that community.
q
D(TM) decomposes diversity estimates into three
components: the number of units (S), functional evenness [
q
E(T), the extent to which
units are equally dispersed], and mean dispersion [M’, the average distance or the
distinctiveness of these units]. Functional diversity measured as
q
D(TM) is maxi2 Applying Remote Sensing to Biodiversity Science
sums the branch lengths among species within a community (from the root of the
phylogeny to the tip). One feature of this metric is that it scales with species richness
because as new species are added into the community, new branch lengths are also
added. Other metrics were subsequently developed that calculate the mean evolutionary distances among species independently of the number of species [e.g., mean phylogenetic distance (MPD, Webb 2000b; Webb et al. 2002) or phylogenetic species
variability (PSV), Helmus 2007]. Helmus (2007) developed two more phylogenetic
diversity metrics that scale either with richness or by incorporating species abundances. Phylogenetic species richness (PSR) increases with the number of species, but
reduces the effect of species richness proportionally to their degree of shared ancestry.
Phylogenetic species evenness (PSE) is similar to PSV but includes abundances by
adding individuals as additional tips descending from a single species node, with
branch lengths of 0. Chao et al. (2010) defined the phylogenetic Hill number,
q
D(T),
as the effective number of equally abundant and equally distinct lineages and phylogenetic branch diversity,
q
PD(T), as the effective total lineage length from the root
node (i.e., the total evolutionary history of an assemblage) (Chao et al. 2014).
Phylogenetic endemism is another aspect of biodiversity that can be estimated
from phylogenetic information and range maps of species (Faith et al. 2004).
Phylogenetic endemism can be simply defined as the quantity of PD restricted to a
given geographic area. This metric thus focuses on geographic areas, rather than on
species, to discern areas of high endemism based on evolutionary history for conservation purposes.
2.7.4 Functional Diversity
Widely used metrics of functional diversity consider the area or volume of trait
space occupied by a community of species, the distances of each species to the center of gravity of those traits, and the trait distances between species (Mouillot et al.
2013). Functional attribute diversity (FAD) is a simple multivariate metric calculated as the sum of species pairwise distances of all measured continuous functional
traits (Walker et al. 1999). Villeger et al. (2008) developed a series of functional
diversity metrics that incorporate trait dispersion and distance among species as
well as species abundances, including functional richness (FRic), functional divergence (FDiv), and functional evenness (FEve). Building on the framework of
Villeger et al. (2008), Laliberté and Legendre (2010) developed functional dispersion
(FDis), a functional diversity metric that is independent of species richness and can
include species relative abundances (Table 2.1).
Scheiner’s functional trait dispersion [
q
D(TM), Scheiner et al. 2017] calculates
the effective number of species (or units) that are as distinct as the most distinct species (or unit) in that community.
q
D(TM) decomposes diversity estimates into three
components: the number of units (S), functional evenness [
q
E(T), the extent to which
units are equally dispersed], and mean dispersion [M’, the average distance or the
distinctiveness of these units]. Functional diversity measured as
q
D(TM) is maxi2 Applying Remote Sensing to Biodiversity Science