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| Analyses of species-diversity patterns of remote islands have been
crucial to the development of biogeographic theory, yet little is
known about corresponding patterns in functional traits on
islands and how, for example, they may be affected by the
introduction of exotic species.We collated trait data for spiders and
beetles and used a functional diversity index (FRic) to test for
nonrandomness in the contribution of endemic, other native (also
combined as indigenous), and exotic species to functional-trait space
across the nine islands of the Azores. In general, for both taxa and
for each distributional category, functional diversity increases with
species richness, which, in turn scales with island area. Null simulations
support the hypothesis that each distributional group contributes
to functional diversity in proportion to their species richness.
Exotic spiders have added novel trait space to a greater degree than
have exotic beetles, likely indicating greater impact of the reduction
of immigration filters and/or differential historical losses of indigenous
species. Analyses of species occurring in native-forest remnants
provide limited indications of the operation of habitat filtering of
exotics for three islands, but only for beetles. Although the general
linear (not saturating) pattern of trait-space increase with richness
of exotics suggests an ongoing process of functional enrichment
and accommodation, further work is urgently needed to determine
how estimates of extinction debt of indigenous species should be
adjusted in the light of these findings. | |
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