Abstract:
Will the ongoing extinction crisis cause a severe loss of evolutionary information
accumulated over millions of years on the tree of life? This question has been largely
explored, particularly for vertebrates and angiosperms. However, no equivalent effort
has been devoted to gymnosperms. Here, we address this question focusing on cycads,
the gymnosperm group exhibiting the highest proportion of threatened species in the
plant kingdom. We assembled the first complete phylogeny of cycads and assessed
how species loss under three scenarios would impact the cycad tree of life. These
scenarios are as follows: (1) All top 50% of evolutionarily distinct (ED) species are lost;
(2) all threatened species are lost; and (3) only all threatened species in each IUCN
category are lost. Finally, we analyzed the biogeographical pattern of cycad diversity
hotspots and tested for gaps in the current global conservation network. First, we
showed that threatened species are not significantly clustered on the cycad tree of
life. Second, we showed that the loss of all vulnerable or endangered species does not
depart significantly from random loss. In contrast, the loss of all top 50% ED, all
threatened or all critically endangered species, would result in a greater loss of PD
(Phylogenetic Diversity) than expected. To inform conservation decisions, we defined
five hotpots of diversity, and depending on the diversity metric used, these hotspots
are located in Southern Africa, Australia, Indo-Pacific,
and Mexico and all are found
within protected areas. We conclude that the phylogenetic diversity accumulated over
millions of years in the cycad tree of life would not survive the current extinction crisis.
As such, prioritizing efforts based on ED and concentrating efforts on critically
endangered species particularly in southern Africa, Australia, Indo-Pacific,
and Mexico are required to safeguarding the evolutionary diversity in the cycad tree of life.
