[Taxacom] NZ biogeographers Annual Exam Q5

John Grehan calabar.john at gmail.com
Wed Feb 15 10:24:17 CST 2017


NZ biogeographers Annual Exam Q5

How does the concept of dynamic metapopulation apply to Oligocene survival
in New Zealand?

“Continuity of some land through the Oligocene does not mean that land has
persisted at any one point; instead, emergent land probably occurred at
different places at different times. In this environment, clades would
survive as dynamic complexes of populations.

For example, in the dipteran family Empididae, the “*Chelipoda*-like group”
is confined to Zealandia (New Zealand, Lord Howe Island, New Caledonia) –
continental crust that rifted from Gondwana – and Vanuatu, part of the
Pacific island arc that rifted from Gondwana in the Cretaceous. Plant
(2010) proposed that the group is “a relictual Gondwana element that has
survived Oligocene drowning as metapopulations persisting *in situ* on
ephemeral islands along arcs, ridges and buoyant crustal blocks…” Many
groups survive as metapopulations on a local, ecological scale; examples
include weedy species that invade forest gaps caused by tree falls, land
slides and so on. A similar process is suggested here for regional
endemics; these have survived more or less *in situ* in their regions by
constantly dispersing to newly emerged islands.

Campbell et al. (2008: 45) wrote that “If it [Zealandia] was completely
immerse, what happened to terrestrial life? It either perished or survived
on ephemeral short-lived islands for which there is little geological
evidence”. The evidence from geology, paleontology, and biogeography
discussed earlier suggests that the latter option is the most probable.
While some biologists have accepted that the entire terrestrial biota was
wiped out, most have accepted that communities survived the flooding on
small, ephemeral islands. Even small islands can maintain very diverse
biotas, as seen in Stewart Island, the islands off Northland, and New
Caledonia, for example. This indicates that many terrestrial taxa endemic
to areas around active plate margins do not require land that is persistent
over geological time, and small islands in the shallow New Zealand seas
would have allowed the survival of taxa through the Oligocene. In addition,
the constantly changing coastlines would have facilitated local
differentiation.”


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