Biodiversity Conservation and Phylogenetic Systematics

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extinction and greater than random loss of phylogenetic diversity seemed intuitive;
if two sister species are lost to extinction, not only do we lose the unique phyloge-
netic diversity captured in the branches from which they subtend, but we also lose
the ancestral branch that is shared between them (see Fig. 2 ). However, in a more
recent study, again using simulations, but this time assuming both a more realistic
model of diversifi cation and a range of phylogenetic signal in extinction probabili-
ties, Parhar and Mooers ( 2011 ) suggested that the loss of phylogenetic diversity
under phylogenetically non-random extinctions was more or less indistinguishable
from random (see also Heard and Mooers 2000 ). Seemingly, the observation of
phylogenetic signal in extinction risks and the non-random loss of phylogenetic
diversity are not necessarily connected directly.
Observations for greater than random losses of phylogenetic diversity that have
been inferred for many clades under realistic extinction scenarios likely refl ect the

ab

c

Fig. 1 Comparison of branching times for different tree reconstruction models of size 128 tips. a
Coalescent model in which branching clusters towards present; b pure birth model in which all
lineages have an equal probability of splitting (b = 1.0) and no lineages go extinct (d = 0); c birth-
death model in which lineages have equal rates of splitting and extinction (birth = 1.0, death = 0.2)

Reconsidering the Loss of Evolutionary History: How Does Non-random Extinction...