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NEWS & VIEWS RESEARCH
during the star’s red-giant phase. According
to this hypothesis, the two close-in planets
formed anew, after the star receded from its
red-giant phase, from material that was left
behind when the star expelled its outer layers.
Surveys that have searched for close-in
planets orbiting evolved stars have demonstrated a lack of such objects7–9. And yet
Charpinet and colleagues’ results buck this
trend by revealing a planetary system in a
startlingly tight orbit. One way to resolve
this apparent discrepancy is to postulate that
close-in massive planets (that would have been
easily detected by the previous surveys) are
almost, but not completely, destroyed during
the red-giant phase of stellar evolution: their
small, dense cores may survive.
Stars such as the Sun spend billions of years
converting hydrogen into helium before
undergoing a quick and violent growth phase
to become red giants. The expansion of the
Sun to its red-giant phase will surely kill off
all life on Earth in the process. However,
the existence of planets orbiting an evolved
star points to an interesting possibility that
all close-in planets are not entirely destroyed
during stellar evolution. Charpinet and
colleagues’ results therefore have important
implications as we strive to understand the
ultimate fate of planetary systems. ■
Eliza M. R. Kempton is in the Department
of Astronomy and Astrophysics,
University of California, Santa Cruz,
Santa Cruz, California 95064, USA.
e-mail: [email protected]
1. Schröder, K. P. & Smith, R. C. Mon. Not. R. Astron.
Soc. 386, 155–163 (2008).
2. Charpinet, S. et al. Nature 480, 496–499
(2011).
3. Villaver, E. & Livio, M. Astrophys. J. 705, L81–L85
(2009).
4. Green, E. M. et al. Astrophys. J. 583, L31–L34
(2003).
5. Charpinet, S. et al. AIP Conf. Proc. 1170, 585–596
(2009).
6. Van Grootel, V. et al. Astrophys. J. 718, L97–L101
(2010).
7. Johnson, J. A. et al. Astrophys. J. 675, 784–789
(2008).
8. Sato, B. et al. Publ. Astron. Soc. Jpn 60, 539–550
(2008).
9. Wright, J. T. et al. Astrophys. J. 693, 1084–1099
(2009).
have indicated that climate change alone is
unlikely to be the reason7.
A major cause of many of these enigmatic
declines was discovered8 in 1998. The pathogenic fungus Batrachochytrium dendrobatidis
causes chytridiomycosis, a disease that infects
amphibians across a wide range of taxa8,9.
This disease has emerged in many areas, and
has caused entire regional faunas to decline
dramatically, to the point of local extinction.
The major threats to amphibian species include pandemic disease and changes
According to the International Union for Conin climate and in land use. A study of the global distributions of these threats
servation of Nature, many amphibian species
predicts that they will affect most amphibians by 2080. See Letter p.516
became critically endangered between 1980
and 2007, in most cases probably because of
ROSS A. ALFORD
as Hof et al.5 report on page 516 of this issue.
the global chytridiomycosis pandemic7. HabiEver since amphibian declines were rec- tat loss and climate change have received less
odern amphibians are the oldest ognized as a global problem6, it has been attention as causes of amphibian decline, but
extant group of terrestrial verte- suggested that the phenomenon has several threaten many more species in the long run7.
brates, having existed for hundreds causes. Early explanations focused on pol- Climate change may already be affecting the
of millions of years1. Some have undergone lution, habitat loss and climate change7, but course of the chytridiomycosis pandemic, and
very little evolutionary change over this many declines have occurred in relatively its influence is likely to continue during this
period. But amphibians are far from being pristine areas not strongly affected by habitat century, because vulnerability to the disease
primitive animals of low diversity. They are, modification, and far from sources of environ- is strongly affected by weather and climate7,10.
in fact, more diverse than mammals or reptiles mental contaminants. In these cases, analyses
Given the current threats to amphibians, it
— 6,894 species are presently
is crucial to develop plans to proknown2, and the best estimate3
tect their diversity. This requires
for the total number of species
a good understanding of present
is 8,000–12,000. They occupy
and future dangers. Hof et al.5
every terrestrial habitat except
have undertaken the complex
Antarctica and the high Arctic,
task of examining the spatial
and have an important role in
extent of three of the major
nutrient dynamics, in the cycling
threats to the global diversity of
of energy flows between terresamphibians — disease, climate
trial and freshwater systems,
and land-use change. By comand in controlling populations
paring their findings with the
of pest insects1.
spatial distribution of amphibAmphibians are also the
ian diversity, they were able to
terrestrial vertebrates most at
say how the threats have changed
risk of extinction: at least 37%
and will probably change in the
are classed as vulnerable, threatperiod from 1980 to 2080. The
ened or endangered4 (Fig. 1).
authors did this for all three
This figure is certainly an underorders of modern amphibestimate of the risk, because
ians, which differ in their levels
the conservation status of Figure 1 | The edge of destruction. The armoured mistfrog Litoria lorica was
of ecological and taxonomic
about 25% of species remains thought to have been extinct for 17 years, but was rediscovered14 in 2008. Many
diversity: roughly 90% of modunknown 4. Sadly, things are other amphibian species are in decline, a situation that Hof et al.5 predict will
ern amphibians are frogs, 8%
likely to be much worse by 2080, accelerate during the twenty-first century.
are salamanders and 2% are the
EC OLO GY
Bleak future for
amphibians
R. A. ALFORD
M
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RESEARCH NEWS & VIEWS
50 Years Ago
The heavy nuclear explosion
on October 30, 1961, at 8.33.33
g.m.t. at a distance of 1,160 km.
in Novaya Zemlya (presumably
at tropospheric heights) was
recorded at Sodankylä by means of
a seismograph, a microbarograph,
a magnetograph, and a vertical
incidence ionosonde. The
deflection of the microbarograph
took place at 9.42 g.m.t. with an
amplitude of about ± 1 mb … On
October 31, the microbarograph
again showed two very distinct and
strong deflexions, namely, at 18.32
and 21.38 g.m.t. These deflexions
are interpreted as being caused by
round-the-world waves due to the
same nuclear explosion, one being
propagated in the backward, the
other in the forward, direction.
The mean velocity deduced from
these round-the-world waves is
311 m./sec … The waves are
supposed to have been guided in
the spherical shell between the
ground and the stratopause.
From Nature 23 December 1961
100 Years Ago
The Rubber-Planter’s Notebook. By
Frank Braham — This book is what
it purports to be, a handy book of
reference on Para rubber planting,
with hints on the maintenance
of health in the tropics and other
general information of utility to
the rubber planter … The author’s
section on general information
will be found specially useful … for
the young planter going out to the
East for the first time; but for the
older resident in the tropics “drink
as little as possible—fluids inflate
the bowel” is dangerous advice …
If blackwater fever is encountered
death in such cases may be the result
… In these essential rules also
mention of the all-important hot
bath and change at sundown would
have added to their completeness.
From Nature 21 December 1911
less well-known caecilians1. Frogs are far more
widely distributed than the other groups.
Hof et al. used a complex, wide range of
modelling approaches in their study. Briefly,
they used data on the distributions of 5,527
amphibian species in bioclimatic models
to predict the global distribution of the species on a latitude–longtitude grid consisting
of cells 2° × 2° in size. This analysis took into
consideration a broad range of future climate
scenarios proposed by the fourth Intergovernmental Panel on Climate Change. To forecast
the spread of chytridiomycosis, they used a
previously published model11 that predicted
the distribution of the causative fungus B. dendrobatidis. Their data on land use and land-use
changes came from the Millennium Ecosystem
Assessment, a report on the current state and
the future of Earth’s ecosystems.
According to Hof et al.5, the outlook for
amphibians is not good. For frogs — the most
diverse group — the areas most affected by climate change coincide with regions of greatest
species richness. The authors’ models indicate
that, in some of the regions with the greatest diversity of frogs, more than half of the
species will probably be negatively affected by
climate change by 2080. Strong climate-change
impacts are also likely for some salamanders,
particularly tropical faunas.
The models also suggest that land-use
changes, especially in tropical regions, are
likely to have strong negative effects on
amphibians in some of the areas that have high
levels of amphibian diversity. Finally, they predict that the distribution of B. dendrobatidis,
and thus possibly of chytridiomycosis, will be
focused in temperate and mountainous areas.
This is better news for frogs, which reach their
peak diversity in the lowland tropics, but may
be bad news for salamanders, whose centre of
diversity is in northern temperate regions.
Possibly the worst news is that, on the whole,
the areas most affected by each category of
threat do not coincide geographically: less
than half of the grid cells in the 25% of land
most threatened by any one factor are also in
the 25% most threatened by any other factor.
Because the threats are spread out, more than
half of the total geographic distribution of
each major amphibian taxon is in areas that
Hof et al. predict will be highly affected by at
least one of the three threat factors by 2080.
The picture becomes worse when only the
most diverse faunas are considered — roughly
two-thirds of the areas that have the highest
diversities of frogs and salamanders are likely
to be highly threatened in some way.
The effects of major changes in land use will
probably be as strong as, or even stronger than,
Hof and colleagues assume, because the complex life histories of amphibians may render
them particularly vulnerable to the disruptive effects of habitat modification12. But in
other respects, the exceedingly gloomy picture presented by the authors might turn out
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to be too pessimistic. For example, the exact
effects of climate change and chytridiomycosis on amphibians are not known, and so their
overall impact may be less than is predicted5.
The somewhat coarse grid used in Hof and
colleagues’ bioclimatic modelling might also
obscure small-scale variations that could allow
species to avoid the negative effects of climate
change by shifting their habitat ranges relatively short distances, or simply by changing
how they use their existing ranges (for example, by choosing less exposed retreat sites)5,7.
More­over, the authors’ analysis equates the
presence of B. dendrobatidis to negative conservation effects of chytridiomycosis, but the
impact of the disease varies strongly among
regional faunas, ranging from disastrous population collapses in some areas to little or no
effect in others9,13.
On the other hand, some of Hof and coworkers’ results may be overly optimistic. For
example, they did not model possible nonadditive impacts of threats, such as the strong
possibility that the threat of epidemic outbreaks of chytridiomycosis may worsen with
changing climate7,10, or that habitat modification may restrict amphibians’ ability to resist
climate change by altering their habitat preferences5,7. Nevertheless, their work is a valuable
step towards a true understanding of overall
threat levels to an iconic group of animals. It
is also a sobering reminder of how much critical information is needed before we can truly
understand the extent of anthropogenic threats
to global biodiversity, or be fully prepared to
rationally manage them. ■
Ross A. Alford is at the School of Marine
and Tropical Biology, James Cook University,
Townsville, Queensland 4811, Australia.
e-mail: [email protected]
1. Alford, R. A., Richards, S. J. & McDonald, K. R. in
Encyclopedia of Biodiversity (ed. Levin, S. A.) 1–12
(Elsevier, 2007); http://dx.doi.org:10.1016/
B0-12-226865-2/00013-4.
2. www.AmphibiaWeb.org (accessed 27 November
2011).
3. Parra, G. et al. in Amphibian Conservation Action
Plan: Proc. IUCN/SSC Amphibian Conserv. Summit
(eds Gascon, C. et al.) Ch. 10 (IUCN, 2005).
4. IUCN Red List of Threatened Species. Version
2011.2. www.iucnredlist.org (downloaded
27 November 2011).
5. Hof, C., Araújo, M. B., Jetz, W. & Rahbek, K. Nature
480, 516–519 (2011).
6. Blaustein, A. R. & Wake, D. B. Trends Ecol. Evol. 5,
203–204 (1990).
7. Alford, R. A. in Ecotoxicology of Amphibians and
Reptiles 2nd edn (eds Sparling, D. W., Lindner, G.,
Bishop, C. A. & Krest, S. K.) 13–46 (CRC Press, 2010).
8. Berger, L. et al. Proc. Natl Acad. Sci. USA 95,
9031–9036 (1998).
9. Lips, K. R. et al. Proc. Natl Acad. Sci. USA 103,
3165–3170 (2006).
10.Pounds, J. A. et al. Nature 439, 161–167 (2006).
11.Rödder, D., Kielgast, J. & Lötters, S. Dis. Aquat.
Organ. 92, 201–207 (2010).
12.Becker, C. G., Fonseca, C. R., Haddad, C. F. B.,
Batista, R. F. & Prado, P. I. Science 318, 1775–1777
(2007).
13.Daszak, P. et al. Ecology 86, 3232–3237 (2005).
14.Puschendorf, R. et al. Conserv. Biol. 25, 956–964
(2011).