What types of frogs live in northern Australia?
Two families of frogs make up most of the species found in
northern Australia: the Hylidae — the tree frog group which
occurs worldwide — and the Myobatrachidae — a diverse
group of generally smaller frogs restricted to Australia and New
Guinea.
The frogs in the Hylidae are often conspicuous frogs and the
group includes many species adapted to life in trees. Tree frogs of
the genus Litoria dominate this group with over 30 species
found in northern Australia. Many of these generally large frogs
feature toe pads that allow them to climb tree trunks and walls.
Litoria caerulea, the common green tree frog is a well known
member of this group and there are several frogs in this genus that
have green bodies — presumably to help camouflage them amid
green leaves.
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A hylid frog: the long-snouted frog, Litoria longirostris
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Not all Litoria, however, live in trees — some
species live in wetlands, or riverbanks away from trees. Most of
the other Hylid frogs in north Australia belong to the genus
Cyclorana (see above) and while these are also often large
frogs, they are not adapted to living in trees, but rather to
burrowing in the ground or living in open grasslands.
The Myobatrachids are a diverse group of frogs that are only
found in Australia and New Guinea. There are a bit under 40
Myobatarachid species found in north Australia. The group includes
some smaller frogs: the Crinia genus generally known as
“froglets” and the Uperoleia genus generally
known as “toadlets”. Some of the most well-known frogs
in Australia belong to another Myobatarachid genus –
Limnodynastes – and the striped marsh frog L.
peronii that many people would have seen in Sydney is also
found in some locations in north Queensland.
Hylid and Myobatarchid frogs are thought to have been in
Australia for a very long time — from before it broke
away from what is now Antartica, but another significant group of
north Australian frogs looks to have arrived later on from the
north.
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A Myobatrachid frog, the northern bullfrog
Limnodynastes terraereginae
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The two genera of the Microhylidae or
“narrow-mouthed” frog family found in Australia are all
found in north Australia and are linked to frogs in New Guinea.
These frogs are generally small, often with rounded bodies. Four of
the five species of the whistlefrogs (Austrochaperina) can
be found in the forests of Cape York Peninsula, and the other
species is found in the Top End of the NT. Similarly all 13 species
of nurseryfrogs (Cophixalus) are found in rainforests of
north Queensland and Cape York Peninsula. Many nurseryfrogs are
found in very restricted areas of high altitude or
“montane” rainforest and for this reason are thought to
be threatened by climate change.
Australia has a single member of the “true” frog
family Ranidae. The Common frog in Britain is a Ranid and the
Australia Ranid, Rana daemeli is known as the Australian
frog. It is likely, however to be a relatively “new”
Australian and a recent invader from the north. It is found in Cape
York Peninsula and restricted parts of the Northern Territory.
Not just another frog: the cane toad Bufo
marinus
What’s the difference between frogs
and toads?
Toads are scientifically classified within the
frog Order – the Anura – so technically they are just
another frog. However, species commonly called “toads”
usually live on land and have a dry, warty skin, whereas those
called “frogs” often prefer moist habitats and have
moist, smooth skins. The “true toads”, including the
cane toad, are members of the family Bufonidae, but there are other
frogs called “toads” such as the spadefoot toads of the
genus Notaden, which has four species in Australia.
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Australia’s only introduced frog is the most notorious
“frog” in Australia – the cane toad Bufo
marinus. Introduced deliberately to north Queensland in 1935 to
control the agricultural pest, the cane beetle larvae, the cane
toad has since become a significant pest in its own right and has
spread across tropical Australia, approaching the borders of
Western Australia by early 2007.
How diverse are north Australian amphibians?
Although it is home to many frog species, North Australia does
not have a particularly diverse array of amphibians compared to
other tropical areas of the world. Australia has no salamanders or
caecilians (worm-like amphibians) and its tropical frog fauna is
dominated by three families comprising a bit over 100 species.
Compare these figures to Indonesia which has around 300 recorded
amphibian species across eight families with more than a single
species, or Ecuador with around 450 species across 11 families with
more than a single species. Indeed as most tropical areas have been
more poorly surveyed for frogs than has northern Australia, their
diversity is probably even greater than we find here. The map below
shows global species diversity for amphibians, with the most
diverse areas being in tropical South America and Africa.
Why does north Australia have relatively low amphibian
diversity?
Two reasons are worth considering here:
Compared to the areas with the highest amphibian diversity north
Australia does not have large areas of tropical rainforest. As
outlined above, frogs are remarkably adept at surviving in the
seasonally dry savannas, however, savannas do not provide the same
range of stable habitats with plenty of insect food for frogs as
tropical rainforests do. 82% of frog species around the world are
found in forests.
Recent studies have shown that the most recent great increase in
amphibian diversity occurred in late Cretaceous and early Tertiary
Periods, around 80–50 million years ago. By this stage
Gondwana had started to break up and Australia was already isolated
from what would become centres of amphibian diversity in South
America and Africa. Australia remained isolated until relatively
recently, so many of the tropical forest frogs of the world did not
have a chance to reach Australia’s tropical forests.
References
Department of Environment and Heritage (2006)
Infection of Amphibians with Chytrid Fungus Resulting in
Chytridiomycosis – Background Document for the Threat
Abatement Plan, Commonwealth of Australia, Canberra
Hero J.-M., Morrison C., Gillespie G., Roberts
J. D., Newell D., Meyer, E. McDonald, Lemckert F., Mahony M.,
Osborne W., Hines H., Richards S., Hoskin C., Clarke J., Doak N.
and Shoo L. (2007) Overview of the conservation status of
Australian frogs. Pacific Conservation Biology 12, pp
313-320.
Roleants K., Gower D.J., Wilkinson M., Loader
S.P., Biju S.D., Guillaume K., Moriau L., and Bossuyt F. (2007)
Global patterns of diversification in the history of modern
amphibians. Proceedings of the National Academy of Sciences
(DOI:10.1073/pnas.0608378104)
Tyler M. J. (1994) Australian Frogs –
a natural history. Reed Books, Chatswood NSW
