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. 2017 Mar 21;7(8):2735-2746.
doi: 10.1002/ece3.2660. eCollection 2017 Apr.

Integrating biogeography, threat and evolutionary data to explore extinction crisis in the taxonomic group of cycads

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Integrating biogeography, threat and evolutionary data to explore extinction crisis in the taxonomic group of cycads

Kowiyou Yessoufou et al. Ecol Evol. .

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.

Keywords: Biogeography; cycad tree of life; diversity hotspots; evolutionary distinctiveness; extinction risk; gymnosperms.

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Figures

Figure 1
Figure 1
A first complete phylogeny of cycads comprising 339 taxa. Clades with higher or lower diversification rates according to the parametric rate comparison test are indicated by hot or cold colors, respectively. The outgroups were removed for the purpose of diversification rate analysis
Figure 2
Figure 2
Evolutionary distinctiveness of cycad species in relation to (a) threat status and (b) IUCN threat categories
Figure 3
Figure 3
Patterns of remaining PD on the cycad tree of life under different scenarios of species loss. Red line = observed remaining PD in a scenario where (a) the top 50% ED species is lost; (b) all the 215 threatened cycad species are lost; and (c–e) all VU, EN, and CR species are lost, respectively. The histogram depicts the pattern of remaining PD on the tree after equivalent number of species in each scenario is pruned randomly from the tree. The blue line indicates the mean of PD remaining after random pruning
Figure 4
Figure 4
Spatial distribution of multiple cycad diversity metrics across 100 × 100 km equal area grids (Behrmann projection): (a) species richness, (b) phylogenetic diversity, (c) mean species endemism, (d) phylogenetic endemism, and (e) mean EDGE. The map was generated using ArcMap 10.0. Color scales are based on equal interval categories centered on zero and labeled with median values
Figure 5
Figure 5
Hotspots of cycad diversity. Hotspots of (a) species richness, (b) phylogenetic diversity, (c) mean species endemism, (d) phylogenetic endemism, (e) mean EDGE, and (f) cumulative map of all five hotspots combined together. The hotspots are grid cells with the highest 2.5% of the diversity scores (shown in red), and the 5.0% hotspots are shown in yellow. The map was generated using ArcMap 10.0. Color scales are based on equal interval categories centered on zero and labeled with median values
Figure 6
Figure 6
Venn diagram of spatial overlap and mismatch between hotspots of cycad diversity. SR, species richness; PD, phylogenetic diversity; CWE, corrected weighted endemism; PE, phylogenetic endemism; EDGE, evolutionary distinctiveness and global endangerment

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