By Frank Köhler
Australian Museum, 6 College Street, Sydney NSW 2010, Australia
Ever since Europeans have set foot here, Australia has been a pretty exciting place for biologists. While the first reports on hopping creatures and duck billed water moles were initially met with suspicion back in Old Europe, it soon became clear that the continent indeed harbours a unique fauna and flora, which resembled little the biotas found elsewhere in the world. And because the place is big, there has been a lot to discover – and trust me, there still is. In fact, it is estimated that Australia is home to about 600,000 native species of plants and animals, or in other terms, perhaps 10 per cent of Earth’s biodiversity. However, you may be surprised to learn that a whopping three quarters of these species are awaiting discovery. On the other hand, Australia has also suffered the largest documented decline in biodiversity of any continent over the last 200 years due to the grave impact of humans on the natural world. As a result, Australia ranks high amongst the global hotspots of endangered and extinct species (Department of Environment, 2009).
Australian Museum, 6 College Street, Sydney NSW 2010, Australia
Ever since Europeans have set foot here, Australia has been a pretty exciting place for biologists. While the first reports on hopping creatures and duck billed water moles were initially met with suspicion back in Old Europe, it soon became clear that the continent indeed harbours a unique fauna and flora, which resembled little the biotas found elsewhere in the world. And because the place is big, there has been a lot to discover – and trust me, there still is. In fact, it is estimated that Australia is home to about 600,000 native species of plants and animals, or in other terms, perhaps 10 per cent of Earth’s biodiversity. However, you may be surprised to learn that a whopping three quarters of these species are awaiting discovery. On the other hand, Australia has also suffered the largest documented decline in biodiversity of any continent over the last 200 years due to the grave impact of humans on the natural world. As a result, Australia ranks high amongst the global hotspots of endangered and extinct species (Department of Environment, 2009).
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| Amplirhagada boongareensis |
If we seriously want to stop or
at least slow down the current rate of species loss, we need to better
understand how Australian biodiversity is made up, how it is distributed
throughout the continent, and which are the main factors that cause the decline
and ultimately extinction of species. Only then can we develop appropriate
conservation strategies that meet the urgency of the case. Frankly, this seems
to be an awful lot of work. While it is utterly unrealistic to hope we could
gain adequate knowledge of all groups of organisms at once, focussing on a
number of model groups might be the one way to go. Such model groups would then
serve as surrogates for ‘the other 99% of biodiversity’ as so dubbed by Ponder
& Lunney (1999). And that is where land snails come into play. A number of
factors render land snails promising model organisms for conservation related
research. Firstly, Australian land snails display exceptionally high levels of
endemism, which in fact exceed levels found in most other faunal groups. About
98.6% of all native species are endemic to Australia (that is, they occur
nowhere else) (Slatyer et al., 2007). Moreover, marked endemism is found on much
finer spatial scales, with some species having extremely small ranges of a few
square kilometres. This endemism is tightly correlated with low mobility and
acute moisture sensitivity of the organisms – a combination that renders snails
susceptible to changes in their habitat, be it due to climate change or more
direct and localized disturbances from urban development, mining, oil and gas
exploration or other forms of land use.
Exactly for these reasons, land
snails are increasingly targeted in biological surveys and used to monitor the effects
of landscape degradation, environmental change or to evaluate the conservation significance
of certain areas. For example, land snails were the only invertebrate group
surveyed in the Kimberley Island Survey, during which between 2008 and the
little known biota of islands off the remote north-western Australian coast was
surveyed. This project gathered new records of endangered vertebrates, but most
significantly, it also led to the discovery of nearly 100 new species and five
new genera of land snails (Kimberley
Island Survey). This brings us to another favourable aspect of land snails:
Their taxonomic and ecological diversity. Briefly, snails are diverse enough to
allow meaningful analyses of diversity patterns but are not too diverse,
causing ongoing taxonomic nightmares.
Molluscan studies in Australia
look back to nearly 250 years of history. The first species were collected
during explorations and voyages along the coastal fringes. Most significantly,
the early French voyages to Australia yielded over 50 newly described species (Dance, 1986). These species were often
described with dubious or imprecise locality information, which continues to
cause taxonomic difficulties and ambiguity until today (e.g., Köhler, 2012). From
1850 on, when the continent became better known and more densely settled, a
small but proliferous scene of Australian taxonomists begun to flourish. Within
just a hundred years, workers such as James Charles Cox, John William Brazier,
Ralph Tate, Charles Hedley and Tom Iredale, together named more than 1,300
species. While these early works were entirely shell-based, the American
malacologist Alan Solem initiated the modern era of Australian malacology. In
his hallmark work, which incorporated comparative anatomy, particularly genital
anatomy, Solem revised the taxonomy of most Western and Central Australian taxa
and described hundreds of new species (Cameron et al., 2005).
Despite the on-going descriptions
of new taxa, by end of the millennium the number of recognized species had
dropped dramatically to 504 because many previously introduced names were
relegated to synonymies (Smith, 1992).
However, Slatyer et al. (2007) argued that 2000 was a more realistic
estimate for the total number of species throughout Australia. This notion has
largely been confirmed recently. In the last five years alone, the number of
recognized species increased to about 1,200. This increase results primarily
from new descriptions of species but also the removal of names from synonymies
in a monograph of the eastern Australian fauna (Stanisic et al., 2010). Accordingly,
about 750 species are now documented from the mesic eastern fringes of the
continent. In addition, a recent series of taxonomic treatments of
north-western Australian camaenids has probably doubled the number of known
species from this part of the country approximately 350.
Eventually, the current decade
has also seen the first more comprehensive molecular phylogenetic studies of
Australian land snails. Molecular phylogenetic studies, even though still in
their infancies, contributed significantly to disentangle systematic
relationships within several main groups, aided the recognition of
morphologically cryptic species, and provided intriguing insights into patterns
of land snail evolution across Australia (e.g.,
Hugall & Stanisic, 2011; Criscione et
al., 2012; Köhler & Johnson, 2012). We learned that the
diversity of land snails throughout Australia is governed mainly by
availability of water and complexity of habitat. In addition, factors, such as
distribution of surface layers of limestone and historical habitat
fragmentation due to increased acidification since the Tertiary have played an
important role in lineage diversification by creating faunal refuges both on
spatial and temporal scales. These factors shaped the distributions of many
taxa, which display recurrent patterns of western vs. eastern, peripheral vs.
interior and northern vs. southern distributions. The highest diversity of
species is found in the eastern Australian mesic zone, which harbours several
major land snail radiations, such as the Camaenidae, Charopidae, Helicarionidae
and Rhytididae. Additional hotspots of diversity are found in the Western
Australian Kimberley as well as the rocky ranges of Central Australia. These
regions, however, boast radiations of only one land snail group, the
Camaenidae.
On-going works continue the
taxonomic description of the Australian fauna demonstrating that the process of
discovery is far from over. Large efforts are being made to close survey gaps
(i.e., by conducting helicopter-based surveys in remote regions) but the
vastness and remoteness of the continent and the comparatively small workforce
of taxonomists set limits to the pace of progress. Our on-going studies are
aiming to tie together taxonomic description, phylogenetic inference and
collection-based biodiversity analyses in order to gain deeper insights into
the evolution of Australian land snails and a more comprehensive understanding
of patterns in order to improve current conservation management.
Literature Cited
Australian Government (2013).
Conservation of biodiversity. Online resource at http://www.environment.gov.au/biodiversity/index.html
(looked up 14 February 2013).
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