Phylogenetic and functional
structure
The phylogenetic structure of Caatinga further from roads differed from
randomness at the 10-m x 10-m scale (Table 2), with NRI significantly
overdispersed for woody species (p=0.027) as well as for non-woody
species (p=0.002). Those woody and non-woody species were
phylogenetically overdispersed in plots further from roads for NRI
(Table 2). Woody and non-woody species were phylogenetically clustered
in plots near roads for NTI (Table 2). At the scale of 10-m x 10-m, the
samples near roads presented NTI significantly clustered (Table 2) for
woody species (p=0.037) and for non-woody species (p=0.031). Woody and
non-woody species presented different phylogenetic structure at the 20-m
x 50-m scale as well as at the 10-m x 10-m scale depending on the
distance from roads. Further from roads, NRI shows phylogenetic
overdispersion at both scales (Table 2, Table S3, Figure S2), whereas
NTI shows phylogenetic clustering for plots near roads at both scales
(Table 2).
Calculating phylogenetic structure only with plants possessing traits
related to herbivory (resprouters, urticants or toxic, succulents with
spines), the traitNTI was significantly higher than zero in plots near
roads, indicating functional clustering and closer relatedness among
individuals than by chance (Table 3). Calculating phylogenetic structure
with plants with all traits, the traitNRI of plots near roads was
significantly greater than zero, indicating phylogenetic clustering,
that is, closer relatedness than by chance (Table 3). These results show
that environmental filtering near roads filters in species
resilient/resistant to herbivory throughout the entire phylogenetic
tree, but especially towards the tips of the phylogenetic branches.