Monday, 3 March 2008

Frog hot spots

Australia is home to more than 200 native frog species. The fauna is unusual in that it is dominated by three families — Hylidae, Microhylidae and Myobatrachidae. The first two families are widespread in warmer parts of the world, whereas the latter is endemic to Australia and New Guinea. Although diverse elsewhere, only one species of Ranidae occurs in the country (Rana daemelii in NE Queensland). No other amphibians are indigenous. No native bufonids or pipids, no salamanders, newts or caecilians.

But if you want frogs, we've got 'em.

The highest diversity occurs in the tropics. Western Arhemland (Northern Territory), the Wet Tropics (NE Queensland) and southern Queensland – northern New South Wales are all hot spots containing 30 or more species. Diversity drops off rapidly away from the coast. Much of inland Australia is home to only one or two species.

Slatyer, Rosauer and Lemckert (2007) examined patterns of endemism in Australian frogs. On analysing almost 100,000 records from 75% of the country — there are no records from a large part of the Nullabor Plain and Western Desert — they found that many of the areas with middling diversity were actually high in endemic species.

Patterns of (a) weighted endemism and (b) species richness for Australian anurans (Slatyer et al.) Click for larger version.

By weighting endemics according to the size of their ranges (the smaller the range, the greater the weighting), they identified 11 hot spots with high endemism scores. Apart from the expected areas (mentioned above), other locations, such as McIlwraith and Iron Ranges on Cape York Peninsula, the Townsville, Eungella and Gladstone regions (Queensland) and Walpole, Bunbury – Augusta and Mitchell Plateau regions (Western Australia), were also packed with endemics.

Slatyer and colleagues propose that this type of analysis should be considered in determining locations of conservation significance. In that case, the analysis must be applied to a range of taxa. Using a similar method, Crisp et al. (2001) identified endemic hot spots for plants, which also included all of the above plus Tasmania, Adelaide and Kangaroo Island, the Australian Alps and the Sydney sandstone. None of these were of significance in the frog study. But neither the frog or plant study picked up central Australia as an area of endemism, although there are numerous short-range endemic snails in that region … The study highlights the complex relationship between diversity and endemism. It's not always easy to spot. Caveat conservator.

Patterns of corrected weighted endemism for Australian plants (Crisp et al.)

Crisp, MD, Laffen, S, Lindner, HP & Monro, A. (2001). Endemism in the Australian flora. Journal of Biogeography 28: 183 – 198.

Slatyer, C, Rosauer, D & Lemckert, F. (2007). An assessment of endemism and species richness patterns in the Australian Anura. Journal of Biogeography 34: 583 – 596.

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