Functional and phylogenetic
diversity
Functional and phylogenetic diversities are different dimensions of the
biodiversity and fundamental to test the hypothesis that Caatinga
vegetation near roads will exhibit decreased taxonomic, functional and
phylogenetic diversity compared to Caatinga vegetation far from roads.
In order to analyze functional diversity, four indexes were used:
functional richness (FRic), functional evenness (FEve), functional
divergence (FDiv) (Villéger et al. , 2008) and functional
dispersion (FDis) (Laliberté & Legendre, 2010). Functional richness
represents the amount of functional space filled by the community, while
functional evenness quantifies the regularity that the functional space
is filled by the species, weighing their abundances. Functional
divergence can be understood as the distribution of the abundance
occupied by the species within the volume of the functional space so
that the divergence is low when the most abundant species is close to
the center of the amplitude of the functional traits and high when this
species has extreme trait values. Finally, functional dispersion refers
to the average distance of one species in the multidimensional
functional space for the centroid of all species.
We calculated these indices for all species sampled considering the
characteristics related to tolerance/resistance strategies for herbivory
deterrence: resprouting abilities, succulence with spines,
urticancy/toxicity and annuals. For the woody component, calculations
were made considering the following functional traits: resprouting
abilitiy, urticancy/toxicity, succulents, nitrogen fixers, life form,
endozoochory, maximum diameter (cm) and maximum height (m). For the
non-woody component (herbaceous-sub-shrub), the functional traits
considered were resprouting ability, annuals (therophytes),
urticancy/toxicity, succulents, nitrogen fixers, life form and relative
coverage of each species. All functional diversity indexes were
calculated in R statistical environment (R Development Core Team, 2015),
using the methods, scripts (Villéger et al. , 2008) and the
functions of the FD package (Laliberté & Legendre, 2010).
Phylogenetic diversity was calculated by the sum of the phylogenetic
distance between species in each community using the PD (phylogenetic
diversity) index provided by the Phylocom 4.2 program (Webb et
al. , 2011) and its standardized measure (standardized effect size -
SESPD) calculated through ’picante’ package (Kembel, 2015) in R
statistical environment (R Development Core Team, 2015). The phylogeny
used was constructed in the same way as the phylogenetic structure
described in the next section.
To investigate the effect of disturbance near roads on variation in
community functional and phylogenetic diversity, we tested the
calculated indices statistically. We used Shapiro-Wilk test to verify
normality of the data. We performed an ANOVA for the data with normal
distribution and the Kruskal-Wallis test for distribution-free data
(Zar, 1996).