[Taxacom] Original biotas

[John Grehan]

Many biogeographers in (and perhaps outside) New Zealand have looked to the
invocation of New Zealand as having some form of original 'pure' existence.
This has been variously expressed in terms of an original 'Gondwana',
'Tasmantis', or 'Zelandia' biota that become the icons of modern political
identity. But biogeography shows that such geographic or geological
entities are more complex and problematic for any effort to concoct a
defining biological essence. Some comments about this complexity by Heads
are as follows:


"It is sometimes assumed that the oceanic terranes were devoid of
terrestrial life when they collided with Gondwana, and that they emerged so
close to the Gondwana coast that they were colonized solely by the mainland
biota. This model conforms to the process outlined in the theory of 'island
biogeography' (MacArthur and Wilson, 1967); proto-New Zealand was formed by
uplift along the margin of Gondwana, and 'the origins of the earliest
colonists seem straightforward' (Winkworth et al., 2002b: 514). In this
model, at the time of later rifting from Gondwana, the biota of the
Zealandia was 'identical' to that of Gondwana (Campbell and Hutching,
2007). Lee et al. (2010: 29) wrote that 'early Zealandia ought to have
contained a mammalian fauna similar to that of eastern Gondwana at the time
of complete separation at c. 60 million years ago'.


Despite these suggestions, there is no real need to think that the arc and
seamount terranes that were integrated into New Zealand were populated only
from the Gondwana mainland, or that they had a biota like that of the
mainland. Nor is it necessary to assume that the biotas of Gondwana or its
rifted daughter fragments, including Zealandia, were ever homogenous. Many
Tasman-Polynesian distributions indicate that the plants and animals of the
arcs and intraplate volcanic on the Pacific and pre-Pacific plates were
just as significant for Tasman region biogeography as those of Gondwana. It
is unlikely that Gondwana was full of terrestrial life and the entire
Pacific and pre-Pacific plates empty. There were always many islands in the
Pacific region, even before the formation of the current Pacific basin, and
even a small tropical islands, let alone a large archipelago, can maintain
a diverse biota. Understanding the biogeography of the Tasman region
requires understanding the history of the life of the central Pacific,
together with that of Gondwana and Tethys.