[Taxacom] strike-slip fault biogeography

[John Grehan]

Some nice examples that have a bearing on our understanding of how
dispersal of organisms works is provided in Heads? book with respect to
disjunctions across the West Caledonian Fault Zone. Heads notes: ?Many taxa
endemic on the Gande Terre ultramafics are widespread there, but other
ultramafic taxa have a more restricted range. There is often a major
bioeographic break between taxa of the north-eastern ultramafic belt and
relatives on the southern massif, separated by the West Caledonian fault.
Some taxa show a boundary at the fault and others show a remarkable dextral
disjunction along it, with populations in the north-west separated by more
than 100 km from those in the south. In all, 86 examples of the disjunction
in morphological taxa of plants, and moths and lizards have been mapped
(Heads, 2008a), and two examples are shown in Figure 8.20. Cases documented
in recent studies include Taeniophyllum muelleri (Orchidaceae), also
present in northeastern Australia and New guinea) (Pignal and Munzinger,
2011). Another example, Acianthus amplexicaulis (Orchidaceae), is disjunct
along the West Caledonian fault and is also disjunct in north-eastern
Australia.


The West Caledonian fault is controversial; some geologists deny that it
exists (Cluzel et al., 2001) while others interpret it as a major structure
that has underdone 150-200 km of horizontal displacement since the Mionce
(Brothers and Blake, 1973; Rawling and Lister, 1997, 1999). Biogeographic
data also support the idea that the fault is important and that it has
undergone large-scale strike-slip movement. The fault or fault zone has
caused the biological disjunction by pulling populations apart, as
discussed above for the New Zealand Alpine Fault (Chapter 7).?



John Grehan