Phylogenetically clustered extinction risks do not substantially prune the Tree of Life

Area of Science:

• Ecology and Evolutionary Biology
• Biodiversity Science
• Conservation Biology

Background:

• Anthropogenic activities are accelerating biological extinction rates.
• Projected extinctions may result in disproportionately large losses to the Tree of Life compared to random extinction events.
• Heritable extinction risk, where entire higher taxonomic groups face extinction, is a proposed driver of this non-random loss.

Purpose of the Study:

• To investigate whether phylogenetically clustered extinction risks are sufficient to cause extensive loss of phylogenetic diversity (PD).
• To determine the conditions under which extinction risk patterns lead to significant pruning of the Tree of Life.

Main Methods:

• Simulated Yule trees and evolved extinction risks across various heritability levels (Pagel's λ).
• Assessed the impact of different extinction risk levels, tree sizes, tree balance, and diversification rate heterogeneity.
• Compared PD loss under clustered extinction scenarios against random extinction models.

Main Results:

• Phylogenetically clustered extinction risks alone are not sufficient to cause substantial PD loss.
• Significant PD loss (up to 20% above random) occurred only with extreme combinations of high phylogenetic signal, high extinction probability, and specific tree shapes (coalescent).
• The rate of PD loss increase declined at very high levels of phylogenetic clustering (λ → 10).

Conclusions:

• The extensive loss of phylogenetic diversity requires an interplay between tree shape characteristics and a tendency for extinction risk to be higher in species-poor clades.
• Non-random extinction patterns, particularly when combined with specific evolutionary and diversification histories, are crucial for understanding major losses to biodiversity.