Data from: Assessing vulnerability of functional diversity to species loss: a case study in Mediterranean agricultural systems

Increasing land-use intensification is leading to biodiversity losses
world-wide, which can reduce the functioning of ecosystems. However, it is
increasingly clear that not all species are equally important for
ecosystem processes: whereas the loss of a functionally unique species may
reduce the capacity of the community to perform some functions, losing a
functionally redundant species should have a much smaller impact.
Assessing the vulnerability of functional diversity (FD) to species
extinctions can help to predict the impacts of land-use intensification.
This approach consists in ranking species according to their risk of
extinction and then estimating the trajectory followed by FD as species
are lost from local communities. However, the most widely used FD indices
are not independent of species richness, being much more sensitive to the
loss of species in species-poor than in species-rich sites. This may
result in misleading interpretations, affecting our ability to rank
communities according to the vulnerability of their FD to species loss, by
confounding it with the initial level of species richness. Here, we
propose comparing the trajectory of FD under the most plausible order of
species loss with that followed under random species losses as an
effective way to remove the trivial effect of species richness in the
assessments of vulnerability to species loss. After decoupling
vulnerability from species richness, we used it to analyse the effect of
agricultural intensification on the vulnerability of arable plant
communities in Mediterranean agricultural fields. Our results show that
management strategies aiming to increase the functionality of these
systems should focus on intermediately intensified fields, where small
reductions in the level of intensification are likely to benefit arable
plant diversity, increasing the number of species and FD and decreasing
the vulnerability of FD to species losses. Removing the effect of species
richness is essential to attain unbiased estimations of the vulnerability
of communities to species loss, especially when species-poor communities
are considered. Combining vulnerability with information on taxonomic and
functional diversity appears as a promising tool to inform decision-making
processes, anticipating the effects of local extinctions.