Résumé
Extinction has increased as human activities impact ecosystems.
Conservation assessments for the IUCN red list are a fundamental tool in
aiding the prevention of further extinction, yet, relatively few species
have been thoroughly assessed. To increase the efficiency of assessments,
novel approaches are needed to highlight threatened species that are
currently data deficient. Many Madagascan plant species currently have
extremely narrow ranges, but this may not have always been the case. To
assess this, we used high-throughput DNA sequencing for 2-5 individuals of
each species - reflecting the paucity of samples available for rare
species. We estimated effective population size (Ne) for each species and
compared this to census population (Nc) sizes when known. In each
case, Ne was an order of magnitude larger
than Nc – a signature of rapid, recent population
decline. We then estimated the demographic history of each species,
tracking changes in Ne over time. Five out of ten
species displayed significant population declines towards the present
(68–90% decreases). Our results for palm trees indicate that it is
possible to predict extinction risk, particularly in the most threatened
species. We performed simulations to show that our approach has the power
to detect population decline during the Anthropocene, but performs less
well when less data is used. Similar declines to those in palms were
observed in data deficient species or those assessed as of least concern.
These analyses reveal that Madagascar’s narrow endemics were not always
rare, having experienced rapid decline in their recent history. Our
approach offers the opportunity to target species in need of conservation
assessment with little prior information, particularly in regions where
human modification of the environment has been rapid.