Abstract
Phylogenetic diversity aims to quantify the evolutionary relatedness among the species comprising a community, using the phylogenetic tree as the metric of the evolutionary relationships. Could these measures unveil the evolutionary history of an area? For example, in a speciation hotspot (biodiversity cradle), we intuitively expect that the species in the community will be more phylogenetically clustered than randomly expected. Here, using a theoretical simulation model, we estimate the ability of phylogenetic metrics of current diversity to detect speciation history. We found that, in the absence of dispersal, if the incipient species do not coexist in the region of speciation (as expected under allopatric speciation), there was no clear phylogenetic clustering and phylogenetic diversity failed to detect speciation history. But if the incipient species coexisted (sympatric speciation), metrics such as standardized effect size of Faith’s Phylogenetic Diversity (PD) and of Mean Nearest Taxon Distance (MNTD) were able to identify areas of high speciation, while Mean Pairwise Distance (MPD) was a poor indicator. PD systematically outperformed MNTD. Dispersal was a game-changer. It allowed species to expand their range, colonize areas, and led to the coexistence of the incipient species originating from a common ancestor. If speciation gradient was spatially contiguous, dispersal strengthened the associations between phylogenetic clustering and speciation history. In the case of spatially random speciation, dispersal blurred the signal with phylogenetic clustering occurring in areas of low or no speciation. Our results imply that phylogenetic clustering is an indicator of speciation history only under certain conditions.
Highlights
Phylogenetic diversity is a facet of biodiversity that is worthy of investigation as it incorporates evolutionary history in community analyses (Webb, 2000; Mazel et al, 2016)
The intuitive expectation that speciation events in an area may lead to declines in phylogenetic diversity (Davies and Buckley, 2011) applies when both the incipient species coexist in the same region of high speciation and not elsewhere
This occurs in our model when speciation is sympatric and there is no dispersal, or when there is a spatially contiguous speciation gradient and local dispersal allows the introduction of the second incipient species in the region of the first incipient species and vice versa
Summary
Phylogenetic diversity is a facet of biodiversity that is worthy of investigation as it incorporates evolutionary history in community analyses (Webb, 2000; Mazel et al, 2016). Phylogenetic diversity has been used as a tool in the selection of conservation targets and designation of protected areas since the 1990s (Faith, 1992; Mazel et al, 2017) This led to the development of spatial phylogenetics, with a line of research focusing on identifying centers of endemism and distinguishing between neo- and paleo-endemism (Mishler et al, 2014; Kougioumoutzis et al, 2021). This approach led to the use of phylogenetic diversity measures to infer biodiversity cradles (areas where species diversify into new species often neo-endemics) and museums (areas where species persist over a long-term evolutionary time) (Dagallier et al, 2020). Despite the intuitive appeal of this approach, the reliability of current phylogenetic diversity data to identify such historic signal of speciation in areas has received limited attention, with studies focusing mainly on the structure of phylogenetic tree (Mazel et al, 2016; Eme et al, 2020), while the factors that affect the efficiency of this surrogacy have not received critical evaluation
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