INVASION OF THE CROCODILES - Rethinking Invasion Ecologies from the Environmental Humanities - page 241

and to what extent this fits with popular understandings/attitudes, and of course
the concept of 'natural'.
The species which have been targeted by invasion biologists are, then, a hybrid
of the following: 'invasive species' which take over ecosystems, which are 'aliens'
(from elsewhere), and are also 'pests' in that they are judged to cause aesthetic or
economic damage to the systems they invade. It should be apparent that crocodiles
only very marginally fulfil the requirements for definition as invasive species, and
only (arguably) as pertains to 'harm'. It is arguable that they negatively impact on
the economic activities and amenity value of systems they inhabit (they also
facilitate economic activity, i.e. ecotourism and crocodile ranching). However they
are not technically 'aliens' if they are recolonising habitat they inhabited in historical
times. It might be argued that they 'take over ecosystems' in that they render whole
waterways possibly unsafe for humans, but there is no biological sense in which
this constitutes an ecological invasion.
Time/scale
Which temporal scale is appropriate for determining nativeness? On a geological
scale, the fossil evidence indicates that what we know as Australia has had croco-
dylians (the order Crocodylia) since the mid-cretaceous period (144-65 mya), since
before it was detached from Antarctica and South America (that is, before
Gondwanaland split up). Many species (some terrestrial) evolved, and crocodilians
occurred from Western Australia through central Northern Territory, the coasts
and interiors of Queensland and New South Wales, and in the interior of South
Australia (Willis, 1991: 291). We know from modern crocodiles that they inhabit
areas where the average temperature of the year's coldest month remains above
10-15°C (50-59°F), though alligators can survive temperatures as low as 4°C
(39.2°F) (Sues, 1992: 24-25). In past interglacial times, then, the Crocodylia were
much more widespread than they are today.
The ancestors of all living crocodylians were the Eusuchia ('true crocodiles') and
the first Eusuchian found in Australia is Isisfordia duncani , an extinct genus related
to the Crocodylia from the mid-Cretaceous. Named after the Australian town
Isisford, near which it was found, and the town's mayor who found it, it was the
basis of claims that the Eusuchia may have originated in Gondwana (the southern
supercontinent), not necessarily Laurasia (the northern supercontinent). The
taxonomy is complex and details are disputed, but it seems reasonably clear that
the mekosuchines were a subfamily of Crocodylians which radiated in the region
during the Eocene (57.8-36.6 mya). The two found in Australia ( Pallimnarchus and
Quinkana ) originated in the Miocene (23.7-5.3 mya), and became extinct in the
Pleistocene (1.6 mya-10,000 years ago). They were replaced by the Indopacific
Crocodylus, whose surviving members include C. porosus and C. johnstoni (Brochu,
2003; Salisbury et al ., 2006). 1
Neither of the two species now existent in Australia is descended from the
ancient species - saltwater or estuarine crocodiles ( Crocodylus porosus ) are thought