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Biodiversity - Extinction by numbers


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How large will be the loss of species through human activities? And over what time period might that loss unfold? Habitat destruction is the leading cause of species extinction. Generally, many of the species found across large areas of a given habitat are represented in smaller areas of it. So habitat loss initially causes few extinctions, then many only as the last remnants of habitat are destroyed. Thus, at current rates of habitat destruction, the peak of extinctions might not occur for decades. But we should not be complacent. On page 853 of this issue, Myers et al.1 document an uneven, highly clumped, distribution of vulnerable species over the world's land surface. Within these 'biodiversity hotspots', habitats are already disproportionately reduced.
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H Iis expected to become largely molecular
(H2) before forming stars. Star formation is
also an inefficient process, so lots of molec-
ular gas should be left over.
By far the most abundant chemical in a
molecular cloud is H2, but it does not radiate
detectable energy at typical cloud tempera-
tures of 20–50 K. Like other astronomers,
Braine et al. have to infer the amount of H2
by observing radiation from accompanying
trace molecules, principally carbon monox-
ide (CO). Crucial to this procedure is the
assumed ratio of H2 to CO in the cloud. This
is known to depend on the chemical abun-
dance in the surroundings, in this case the
TDG. The few existing studies of TDGs sug-
gest that their abundances are sufficiently
like those in our Galaxy to justify Braine et
al.s use of the ‘standard’ CO-to-H2 conver-
sion factor derived for molecular clouds near
the Sun.
Many tidal tails have been searched for
CO (refs 11,12), but it has been detected in
only three13–15. Two serious impediments
prevent us from associating these with true
TDGs. First, the detected CO is nearby and
moving rather slowly with respect to the
probable parent galaxies. It is not obviously
escaping. Admittedly the situation is unclear
because as usual the velocity is measured in
only one direction, and the spatial separa-
tion relies on only two coordinates. Second,
although the CO appears to accompany the
atomic gas, the observations do not distin-
guish between molecules that were pulled
out of the parent galaxy or that were formed
within the ejected H I. The latter is favoured
by observations suggesting that H Iin most
large galaxies extends farther from the centre
of mass than CO, and so should be easier to
remove. Such a distinction is vital if one
wants the ejected material to look like an
irregular dwarf galaxy after leaving the site of
the interaction — a journey requiring more
than 108 years. In the accepted picture, con-
tinuing star formation demands ongoing
formation of molecular gas.
Braine et al.4present the first reasonably
strong case that some TDGs can synthesize
new molecular clouds. The CO in their
clouds is far removed from the parent galaxy
and moving rapidly. It also appears to be
concentrated at the same location as the H I,
and to share its velocity. Coincidence in loca-
tion and motion is expected if the molecules
formed in situ from the atomic gas in the
runaway cloud, but difficult to understand
otherwise. The velocities and distributions
of the H Iand CO are sufficiently similar to
support the case for in situ formation. My
chief reservation is that the CO emission is
sampled at only a few spots — certainly
enough to suggest that it follows the atomic
gas, but too few to make a solid case. More
complete sampling would help.
It is unlikely that all irregular dwarf galax-
ies were once TDGs — for one thing most
dwarfs have fewer heavy elements than the
TDGs measured so far. To explain even the
most element-rich dwarfs, TDGs must sur-
vive as long as 1010 years — the age of a typical
galaxy. The discovery of stars 106–107years
old at the ends of some 108-year-old tidal
tails doesn’t guarantee long-term stability.
Braine et al. propose that in situ formation of
molecules is a good indicator of stability.
I would agree that a gas cloud that is break-
ing up is not a good place to form molecules.
But tidally stripped material is clumpy, prob-
ably on smaller scales than we have yet
probed. It is possible that molecules could
still form within small, stable clumps, how-
ever dispersed. Computer simulations of
interactions cannot yet resolve this issue;
meanwhile I remain sceptical.
One final question: why hasn’t CO been
seen in other tidal features, such as the merg-
ing galaxies shown in Fig. 1? If one assumes
the most reasonable value for the CO-to-H2
conversion factor, then earlier upper limits
on detection are generally consistent with
the CO signals seen by Braine and colleagues.
Again, additional (and more sensitive) data
are needed. The detections of molecular gas
in TDGs are certain to stimulate such obser-
vations, and to lead to a better understanding
of the formation of dwarf galaxies.
Gary Welch is in the Department of Astronomy and
Physics, Saint Mary’s University, Halifax, Nova
Scotia, B3H 3C3, Canada.
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Figure 1 Birthplace of dwarf galaxies?
a, Interacting galaxies in the NGC4676 system,
showing the remarkably straight tail of stars
pulled from one of the two galaxies16. The image
is a greyscale negative of visible light. The black
scale bar shows a distance of 90,000 light years
— about the size of our own Galaxy. b, The same
system seen with a hydrogen filter, so that
atomic hydrogen appears blue, whereas
hydrogen that has been ionized (presumably by
young stars) appears red. Curiously, the
molecular gas expected to accompany these stars
is not found in the tail. Images of similar tails
analysed by Braine et al.4do show signs of
molecular hydrogen, suggesting that these tails
are involved in continuous star formation.
How large will be the loss of species
through human activities? And over
what time period might that loss
unfold? Habitat destruction is the leading
cause of species extinction. Generally, many
of the species found across large areas of a
given habitat are represented in smaller
areas of it. So habitat loss initially causes few
extinctions, then many only as the last rem-
nants of habitat are destroyed. Thus, at cur-
rent rates of habitat destruction, the peak of
extinctions might not occur for decades.
But we should not be complacent. On page
853 of this issue, Myers et al.1document an
uneven, highly clumped, distribution of
vulnerable species over the world’s land sur-
face. Within these ‘biodiversity hotspots’,
habitats are already disproportionately
Conservatively, there are about seven
million species of eukaryote2— a definition
encompassing most organisms that would
be generally recognized as plants or animals
but excluding bacteria, for instance. Most
Extinction by numbers
Stuart L. Pimm and Peter Raven
© 2000 Macmillan Magazines Ltd
of these seven million are animals and about
85% are terrestrial.
Humanity is rapidly destroying habitats
that are most species-rich. About two-thirds
of all species occur in the tropics, largely in
the tropical humid forests3. These forests
originally covered between 14 million and
18 million square kilometres, depending on
the exact definition, and about half of the
original area remains4. Much of the rain-
forest reduction is recent, and clearing now
eliminates about 1 million square kilometres
every 5 to 10 years4–6. Burning and selective
logging severely damages several times the
area that is cleared5,6.
To convert habitat loss to species loss, the
principles of island ecology are applied to the
terrestrial ‘islands’ that remain in a ‘sea’ of
converted land7. The relationship between
number of species and island area is nonlin-
ear, and from this one can predict how many
species should become extinct as the size of
the forest islands shrinks. These doomed spe-
cies do not disappear immediately, however.
How does one go about calculating the
rate of species extinctions from habitat frag-
ments? There have been only a few such esti-
mates, but projections based on a species
survivorship curve with a half-life of roughly
50 years seem reasonable8. Combining the
rate of habitat loss, the species-to-area rela-
tionship and the survivorship curve gives a
crude extinction curve (curve a in Box 1).
From this, we would expect that current
extinction rates should be modest — on the
order of a thousand species per decade, per
million species, a figure that matches other
Because the species–area curve is non-
linear, the clearing to date of half of the
humid forests is predicted to eliminate only
15% of the species that they contain. The
time delays before extinction mean that
many more species should be ‘threatened’
than have already become extinct; that is,
they are thought likely to become extinct in
the wild in the medium-term future. At least
12% of all plants10 and 11% of all birds11
come into this category.
Of course, clearing the remaining half of
the forests would eliminate the other 85% of
species that they contain. The extinction
curve should accelerate rapidly to a peak by
the middle of the twenty-first century if the
rate of forest clearing remains constant. But
it will be upon us sooner if that rate is
increasing — as seems probable4,6.
Once the extinction peak has passed, the
extinction curve declines into the twenty-
second century as species are lost from the
remaining fragments of habitat. The relative
height of the peak depends critically on the
amount of habitat that remains. A value of
5% of remaining habitat (see Table 1 on page
854) would protect about 50% of all the
forests’ species; smaller percentages would
lead to smaller estimates of surviving species.
Modest tinkering with parameters does
not alter the ‘fewer extinctions now, many
more later’ feature of the extinction curve
(curve a in Box 1). But the calculations of
Myers et al.1do. They show that roughly
30–50% of plant, amphibian, reptile, mam-
mal and bird species occur in 25 hotspots
that individually occupy no more than 2% of
the ice-free land surface (see the map on
page 853). That is, terrestrial species with
small geographical ranges are numerous and
they have highly clumped distributions.
Myers et al. exclude the oceans from their
analysis. But there, too, fishes and other
organisms dependent on coral reefs are simi-
larly concentrated12.
Habitat destruction acts like a cookie
cutter stamping out poorly mixed dough9.
Species found only within the stamped-out
area are themselves stamped out. Those
found more widely are not. Moreover,
species with small ranges are typically
scarcer within their ranges than are more
widely distributed species, making them yet
more vulnerable. Consequently, even ran-
dom destruction would create centres of
extinction that match the concentrations of
small-ranged species — the hotspots9.
Worse, however, Myers et al. show that
the cookie cutter is not random — it is
malevolent. In the 17 tropical forest areas
designated as biodiversity hotspots, only
12% of the original primary vegetation
remains, compared with about 50% for
tropical forests as a whole. Even within those
hotspots, the areas richest in endemic plant
species — species that are found there, and
only there — have proportionately the least
remaining vegetation and the smallest areas
currently protected.
Applying the species–area relationship to
the individual hotspots gives the prediction
that 18% of all their species will eventually
become extinct if all of the remaining habi-
tats within hotspots were quickly protected
(curve c in Box 1). Assuming that the higher-
than-average rate of habitat loss in these hot-
spots continues for another decade until only
the areas currently protected remain (curve
b in Box 1), these hotspots would eventually
lose about 40% of all their species. All of
these projections ignore other effects on bio-
diversity, such as the possibly adverse impact
of global warming, and the introduction of
alien species, which is a well-documented
cause of extinction of native species.
Unless there is immediate action to sal-
vage the remaining unprotected hotspot
areas, the species losses will more than dou-
ble. There is, however, a glimmer of light in
this gloomy picture. High densities of small-
ranged species make many species vulnera-
ble to extinction. But equally this pattern
allows both minds and budgets to be con-
centrated on the prevention of nature’s
untimely end. According to Myers et al.,
these areas constitute only a little more than
one million square kilometres. Protecting
them is necessary, but not sufficient. Unless
the large remaining areas of humid tropical
forests are also protected, extinctions of
those species that are still wide-ranging
news and views
VOL 403
24 FEBRUARY 2000
Three projections of how
numbers of species extinctions
in tropical forests may unfold
from forest clearance. Curve a is
the extinction curve on current
estimates, not taking into
account biodiversity hotspots.
According to the relationship
)0.25 (see refs 6–8),
as habitat is reduced from an
original area of
viable species in year
from an original total of
. The
doomed species will die
off with a half-life of 50 years7.
With a constant rate of forest
clearance, this curve takes
time to peak because of the
nonlinear relationship between
species and area, and the time
lags for species to become
et al.
1 identify 25
biodiversity hotspots around
the world, of which 17 are in
tropical forests. These areas
have already suffered
disproportionate loss of
primary vegetation, meaning
that the many species they
contain are under particular
threat of extinction. If all
remaining habitat in hotspots is
saved (as shown in curve c),
some 18% of their species
will be lost. The same half-life
for currently threatened species
is used as in curve a. However,
if the hotspots are cleared in
the next decade to the point
where only currently protected
areas are saved (curve b) then
the total extinctions will be
higher. S. L. P. & P. R.
Extinctions per million species per decade
2000 2020 2040 2060 2080 2100
a, Tropical forest
extinction curve
on current
c, Extinction curve if
all hotspots are saved
b, Extinction curve if
protected hotspots
are saved
Box 1: Extinctions in tropical forests, 2000–2100
© 2000 Macmillan Magazines Ltd
used for measuring femtosecond pulses and
is a close cousin of the pump–probe tech-
nique used in femtochemistry.
For autocorrelation measurements, a
femtosecond pulse is split into two at a beam
splitter. (A beam-splitter functions like a
window at night. In a lighted room you can
see your reflection in the window while
simultaneously being able to see outside.)
The two beams are sent through different
paths, and usually recombine within a crys-
tal with nonlinear optical properties.
Because the harmonic light produced by the
nonlinear crystal is stronger when the two
pulses are overlapped, observing the signal
strength as a function of the difference in the
path length of the two beams gives a
measurement of the pulse’s duration.
Unfortunately, the short duration and
wavelength of attosecond pulses means that
neither traditional beam splitters nor nonlin-
ear crystals are suitable. Papadogiannis et al.
should exceed those in the hotspots within a
few decades (Box 1).
Stuart L. Pimm is at the Center for Environmental
Research and Conservation, MC 5556, Columbia
University, 1200 Amsterdam Avenue, New York,
New York 10027, USA.
Peter Raven is at the Missouri Botanical Garden,
PO Box 299, St Louis, Missouri 63166, USA.
1. Myers, N., Mittermeier, R. A., Mittermeier, C. G., da Fonseca,
G. A. B. & Kent, J. Nature 403, 853–858 (2000).
2. May, R. M. in Nature and Human Society (ed. Raven, P. H.)
(Natl Acad. Sci. Press, Washington DC, 2000).
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Acad. Sci. Press, Washington DC, 1980).
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5. Nepstead, D. C. et al. Nature398, 505–508 (1999).
6. Cochrane, M. A. et al. Science 284, 1832–1835 (1999).
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382–384 (1997).
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1140–1150 (1999).
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(Smithsonian Inst. Press, Washington DC, 1994).
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have sidestepped these problems by splitting
the femtosecond pulse before the attosecond
pulse is produced, and using a rare gas for the
dual purpose of producing and measuring
the attosecond pulses. All characteristics
necessary for measurement are present, but
because production and measurement are
entwined, their measurement is not com-
pletely transparent, so the method is contro-
versial. But the controversy will not last for
long because the basic physics behind the
measurements is well understood.
Although current research is naturally
focused on the production and measure-
ment of attosecond pulses, it is important to
look at the future direction of attosecond sci-
ence. For one thing, it will benefit from the
experience gained in previous experiments
with ultrashort pulses. This is because we
have been performing indirect attosecond
experiments (often referred to as strong-
field science) for a decade or more and the
necessary tools are well developed. For
example, normal visible laser pulses contain
electric fields that change significantly dur-
ing 100 attoseconds (Fig. 1). The electric
field of the light pulse is proportional to the
force that the field exerts on any electrically
charged particle. With modern laser tech-
nology, the forces can be very large and
precisely controlled. So, hidden within the
interactions of intense visible laser light with
matter are attosecond or near-attosecond
phenomena induced by the laser field.
Indeed, indirect attosecond science can
explain the attosecond pulses produced by
Papadogiannis et al. As the electric field of
the laser becomes strong, one of the electrons
is pulled free from an atom in the argon gas.
Once free, it moves in response to the strong
force of the laser; first it is driven away from
the ion, then back. Its path can be compared
to that of a lifeboat launched from a ship in a
stormy sea. The ship (or ion) from which it
detached is an obstacle that remains in the
area and with which it can collide. As with the
lifeboat and ship analogy, the wave deter-
mines the possible time of collision. In the
violent electron–ion collision that may
occur, very-short-wavelength radiation can
be emitted. So the precise synchronization of
the individual attosecond pulses with the
much-longer-wavelength radiation that
produced them (Fig. 1) is not an accident,
but is forced by the field. Quantum mechan-
ics adds ‘fuzziness’ to this essentially classical
description, but does not change it much.
No experiments have yet been performed
with attosecond pulses, and we cannot even
produce an isolated pulse. There are, howev-
er, many ideas and proposals waiting in the
wings, all involving increasingly precise con-
trol over oscillations of the strong laser field.
Once attosecond pulses can be produced
routinely, indirect and direct attosecond sci-
ence will become increasingly integrated.
Whereas the goal behind the development
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VOL 403
24 FEBRUARY 2000
| 845
For the past five years, scientists have
stood on the threshold of generating
attosecond laser pulses but have been
unable to cross it. (An attosecond — 10118 s
— is to one second as one second is to the
age of the Universe.) This may have finally
changed with the publication of a paper by
Papadogiannis et al. (Phys. Rev. Lett. 83,
4289–4292; 1999), who claim to have
measured trains of attosecond pulses. The
previous record for the shortest laser pulse
was 4.5210115 s (4.5 femtoseconds). Pulses
in the femtosecond range led to the develop-
ment of femtochemistry — making it possi-
ble to study chemical reactions in real time
— for which the 1999 Nobel Prize in Chem-
istry was awarded to Ahmed Zewail. But the
new science that will ultimately emerge from
attosecond research will have its own unique
The approach that Papadogiannis et al.
use for generating attosecond pulses has been
under investigation for some time. They use
the short-wavelength harmonics generated
when rare gases (such as argon) ionize as a
result of irradiation from an intense femto-
second pulse. Harmonics occur at multiples
of the frequency of the original femtosecond
pulse. Next, the authors select a set of these
harmonics, which theory indicates should
combine to produce a train of pulses about
100 attoseconds in duration (Fig. 1). Such
pulses have probably already been created in
many laboratories, but no one has been able
to measure them accurately.
Papadogiannis et al. may eventually be
recognized as the parents of experimental
attosecond science because they have actual-
ly measured the duration of these pulses.
Their measurement process is experimental-
ly simple, but theoretically complex. This is
because the production of the attosecond
pulses is intrinsically entwined with the
measurement. They use a technique influ-
enced by autocorrelation, which is widely
Figure 1 Train of attosecond pulses similar to that
produced by Papadogiannis et al. Here, the initial
femtosecond pulse (red) is much shorter than the
one that they used, and the higher-frequency
harmonic radiation (blue) is much more intense
than in their experiment. The offset between the
peak of the initial pulse and of the harmonic
radiation illustrates the delay in the harmonic
emission imposed by the laser field oscillation.
Electric field
Time (femtoseconds, 10–15 s)
Laser physics
Attosecond pulses at last
Paul Corkum
© 2000 Macmillan Magazines Ltd
... Study predicted that approximately 15-37% of terrestrial species will be 'committed to extinction' due to climate-warming scenarios for 2050 [21]. Besides, habitat loss is important cause for organism extinction [22]. For example, it has been reported declining of reptile species in global scale due to several factors including habitat loss [23]. ...
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... Firstly, by producing a dataset representing a globally consistent cropland extent time-series [Potapov et al. 2021]. Cropland expansion is known to have severe adverse effects on natural biodiversity [Pimm & Raven 2000] through loss and fragmentation of habitats [Foley et al. 2005]. The crop mapping was performed in five-year intervals (2000-2003, 2004-2007, 2008-2011, 2012-2015, and 2016-2019); however, for our purpose the net cropland extent change from 2003 to 2019 was considered; pixel values (0-100) represent the percent of cropland dynamic (net loss or net gain) per pixel. ...
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article info abstract The European range of the roller was formerly more extensive, but since the 1980s there has been a long-term decline in numbers and in range, particularly towards the north, including much of northwestern Ukraine. Our specific goals were to reconstruct the environmentally suitable range of the species in Ukraine before the 1980s, gain better knowledge on its requirements, compare the past and current suitable areas, infer the regional and environmental variables that best explain its occurrence, and quantify the overall range change in the country. For these purposes we created a database consisting of 584 findings made in Ukraine, based on a lengthy record of occurrences extending back to 1851: 203 for the period prior to 1980, 91 for records made between 1985 and 2009, and 290 records made between 2010 and 2020. We employed a species distribution modelling (SDM) approach to hind-cast changes in the suitable range of the roller during historical times across Ukraine and to derive spatially explicit predictions of environmental suitability for the species under current climate and a set of factors that were hypothesised to be of importance to roller presence and securing a sufficient food base. SDMs were created for three time intervals (before) using corresponding climate data. SDMs show a decline of suitable for rollers areas in the country from around 86 to 44%. Several factors, including land cover and land use, human population density etc. that could have contributed to the decline of the species in Ukraine, were considered. For example, the loss of area of 'short vegetation' appears detrimental, although recent gains in this respect have favoured the bird in the Chornobyl Exclusion Zone and around, where Landsat images show the change from a previously vibrant agricultural and forestry economy, when crops have been replaced by grasslands. Threats posed to the roller by habitat and land use change are also likely to be compounded by the effects of global climate change. In summary, we suggest climate change, in particular velocity, have been responsible for shaping the contemporary home range of the European roller in Ukraine and perhaps beyond. key words Coracias garrulus, species distribution modelling, ecological niche, climate change, velocity of climate change. cite as Shupova, T., V. Tytar. 2022. Long-term monitoring of the European roller (Coracias garrulus) in Ukraine: is climate behind the changes? GEO&BIO, 23: 154-171. Резюме. Раніше європейський ареал сиворакши був ширшим, але з 1980-х років спостерігається тривале зниження чисельності виду та скорочення його ареалу, особливо на півночі, включаючи більшу частину пн.-зах. України. Мета дослідження полягала в реконструкції ареалу виду в Україні, який існував до 1980-х років, та склався пізніше. При цьому передбачалось отримання поглиблених знань про екологічні вимоги виду, порівняння географічних меж минулих та сучасних територій, придатних для перебування птахів, проведення аналізу факторів, які пояснюють особливості по-ширення сиворакши та дати кількісну оцінку загальних змін ареалу виду в країні. Для цього скла-дена база даних, що складається з 584 знахідок птахів, що гніздилися, зроблених в Україні на основі довготривалих спостережень, реєстрація яких починається з 1851 року: 203 реєстрації за період до 1980 року, 91 для записів, зроблених між 1985 і 2009 роками, і 290 записів, зроблених між 2010 та 2020 роками. Ми застосували підхід, заснований на принципах моделювання поширення видів (SDM), також відомий як «моделювання екологічної ніші», для ретроспективного вивчення змін ареалу сиворакши протягом історичного часу по всій України та отримання просторових прогнозів екологічно придатних для виду територій як за умов поточного клімату, так і минулого клімату, та впливу низки факторів, які за припущенням мають важливе значення для перебування сиворакши та сприяють забезпеченню достатньої бази для живлення птахів. Моделі були створені для трьох ча-сових інтервалів (до) з використанням відповідних кліматичних даних. Моделі показують скорочення екологічно придатних для птахів територій з 86 до 44%. Було розгля-нуто кілька факторів, які могли сприяти погіршенню ситуації для виду в Україні. Наприклад, втра-та площі «низькорослої рослинності» по країні є негативним фактором. Лише у Чорнобильській зоні відчуження та поблизу неї цей процес, як показують знімки Landsat, є зворотній, що сприяло птахам. Загрози, пов'язані зі зміною середовища існування та землекористування, можуть також посилюватися впливом глобальної зміни клімату. Підводячи підсумок, ми припускаємо, що зміна клімату, зокрема її швидкість, спричинила формування сучасного ареалу сиворакші в Україні та, можливо, за її межами. Ключові слова: Coracias garrulus, моделювання поширення видів, екологічна ніші, зміна клімату, швидкість кліматичних змін. Адреса для зв'язку: Володимир Титар; Інститут зоології ім. І. І. Шмальгаузена НАН України; вул. Бог-дана Хмельницького, 15, Київ, 01601 Ukraine;
... The actual number of eriophyoid species is unknown, but more importantly, in recent times there has been a flood of warnings in biodiversity, climate, conservation and ecology journals about major biodiversity losses. Pimm and Raven (2000) estimated that the clearing of 50% of the total area of tropical rainforests, mostly in recent times, had eliminated 15% of the species that they had harboured. Many of those species were likely to have been the highly host-specific eriophyoids. ...
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Coextinction is a major and growing threat to global biodiversity. One of the affected groups is the eriophyoid mites (Prostigmata: Eriophyoidea) which are highly host plant specific. They have been described from an enormous range of annual and perennial plants from grasses to giant forest trees. It is highly likely that there are huge numbers of undescribed eriophyoid species in the subtropical and tropical regions which harbor an extraordinary wealth of plant diversity. The global total of eriophyoid species is estimated to be at least 250,000 but it could be much higher. However, the continuing destruction and degradation of natural habitat, especially tropical forests, and climate change, together pose extreme, on-going threats to the eriophyoid mites because of their vulnerability to co-extinction with their host plants. It has been reported that one third of all the Earth’s plant species are now at risk of extinction. Together with enormous numbers of other invertebrate species, it is highly likely that many thousands of eriophyoid species are disappearing in the current mass extinction event. Population decline and co-extinction, especially of the invertebrates, are greatly accelerating total biodiversity losses. The termination of habitat destruction and degradation; establishment of large, representative protected areas; restoration of degraded areas; and rapid reduction of fossil fuel use, are urgent tasks. However, the long term conservation of biodiversity can only be achieved through comprehensive social, economic and political reforms across the world that prioritize environmental protection, peaceful coexistence, social justice and the sustainable use of resources.
... In India, 54 % of tropical forests are categorised as tropical dry deciduous forests (TDDFs) which are getting converted into speciespoor grasslands and scrublands due to continuous lopping and forest clearing (Singh and Singh, 1989;Singh and Kushwaha, 2005). The principal cause of biodiversity loss and species extinction is habitat destruction of species residing in these forest ecosystems (Koh et al., 2004;Pimm and raven, 2000). Thus, the present scenario intensifies the need for phytosociological studies crucial for proper management and conservation purposes. ...
The aim of the current investigation was to study the effects of anthropogenic disturbances on the vegetation structure of the three Tropical Dry Deciduous Forests of Southern Haryana i.e., Mandhana, Ghasola, and Mandhiali in the Bhiwani, Charkhi Dadri, and Mahendergarh districts, respectively. The data were collected from March, 2020 to March, 2021. The floristic composition was quantified by randomly placing 15 quadrats per site (45 in total). A disturbance index was developed for each site and high, medium and low disturbance areas were identified based on prevailing disturbances that were found to be maximum for Mandhiali (21), followed by Ghasola (16) and Mandhana (9). Ecological parameters such as frequency, density, abundance, basal area, IVI, and diversity indices were calculated for each siteduring the study. A total of 50 species of plants representing 44 genera and 25 families were observed consisting of 14 trees, 9 shrubs, and 27 herbs during the investigation of floristic composition. The species richness decreased with an increase in the disturbance level on the three sites viz., Mandhana (40), Ghasola (33), and Mandhiali (29) respectively. The value of Shannon Weiner diversity index (H’) and Pielou Index of evenness (E) declined with an increasing disturbance while Simpson index of dominance (Cd) increased as the disturbance levels increased across the three sites. The results offer significant evidence that anthropogenic disturbances in arid regions of South Haryana play a vital role in community structure and composition. In a forest ecosystem, anthropogenic disturbances cause habitat fragmentation along with soil erosion, loss of soil fertility and biodiversity, etc. The selected forests are in urgent need of management activities to check the intensity of disturbances by controlling anthropogenic pressure on these ecosystems and save them from further degradation. Thus, the present study intensifies the need for phytosociological studies crucial for proper management and conservation purposes.
Human activities have altered the composition of species assemblages through the introduction of non-native species and the extinction of threatened species. However, it remains unclear whether non-native species can compensate for the loss of threatened species and thus maintain ecosystem functioning. Here we tested whether non-natives are functionally and/or phylogenetically similar (compensation hypothesis) or distinct (shift hypothesis) from native and threatened species on bird assemblages in 267 regions worldwide. We show that non-native species were more functionally distinct from threatened species than expected by chance but more phylogenetically related. Globally, this results in an increase in the functional richness of bird assemblages due to the introduction of new functional traits but a decrease in the phylogenetic richness due to the potential loss of phylogenetically unique threatened species. Furthermore, these patterns vary across continents, revealing the role of human history and footprint across the world and outlining priority areas where international bird conservation should focus. In the context of the biodiversity crisis and the increasing number of non-native species worldwide, the changes in the functional and phylogenetic structure of the bird communities might increase the vulnerability of ecosystems.
The greatest driver of the current biodiversity crisis is habitat loss. Roads are a major contributor to habitat loss because they destroy and fragment habitat, in addition to causing direct mortality. Animals may respond to roads either by avoiding them, thus leading to population isolation, or by attempting to cross them, thus potentially leading to increased mortality and, if so, also to population isolation. We studied the impact of road density on abundance of two snake species: redbelly snakes (Storeria occipitomaculata Storer, 1839) and garter snakes (Thamnophis sirtalis Linnaeus, 1758) around Ottawa, Canada. We hypothesized that roads are detrimental to snake populations due to road avoidance and mortality. Therefore, we predicted that snakes should be less abundant at sites with higher road density in their surroundings. We deployed cover boards at 28 sites along a gradient of road density in 2020 and 2021. We visited sites weekly, counted the number of individuals of both species, and measured snout–vent length (SVL) of all individuals captured. We captured fewer garter snakes at sites surrounded by more roads and fewer redbelly snakes at sites surrounded by more urban habitat. Snakes at sites surrounded by more roads were not smaller. The effects of roads and urbanization on the number of snakes were modest, but indicate decreasing population sizes that could lead to loss of ecological function.
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Urbanization represent a radical transformation of natural habitats that alters all the biotic and abiotic properties governing ecosystems. Urban expansion often results in oversimplified communities, where most specialists decline or disappear and a few generalist or exotic species become dominant. The consequences of urban expansion in mangrove forests are understudied, although these systems have been altered by humans through centuries and the growth of human population in tropical coasts is expected to be faster than in higher latitudes. To assess the importance of indigenous and non-indigenous species in driving temporal and spatial changes in community structure of red-mangrove prop-root macrobenthic communities, we studied heavily altered mangrove forests from two bays from the Caribbean coast of Colombia in 2005 and 2021. In all places/periods, the community richness was low, a few taxa were dominant (11 taxa, out of 40, comprised ~ 90% of the total abundance) and the majority of all taxa (65%) were non-indigenous species whose presence is related with known stressors in urbanized systems. Hence, we suggest that urban mangrove forests are emerging hotspots for non-indigenous biota. Community structure did not change within or between bays, there was a clear, significant turnover of core species between 2005 and 2021, with non-indigenous species playing a prominent role in this variability. This was puzzling –ecological theory asserts that the abundance of a species is related to their permanence: core species are relatively stable through time while rare species appear or disappear– but this may not apply for communities dominated by non-indigenous biota.
The diversity and threats of medium and large‐sized mammals was studied in Abay (Blue Nile) Gorge, Amhara Region, Ethiopia using direct and indirect survey techniques on transect lines crossing natural forest, riverine forest and woodlands. Footprints, camera traps and group discussions were used. Data were analyzed using detrended correspondence analysis, cluster analysis, non-metric multidimensional scaling, and diversity indices. A total of 25 medium and large mammal species belonging to 6 orders and 12 families were recorded. Order Carnivora was the most abundant followed by Artiodactyla, whereas Tubulidentata, Lagomorpha and Procaviida were rare. Leopard is threatened species. The plotting of the detrended correspondence analysis between mammal species and districts showed 61% on axis 1 and 22% on axis 2 and Gozamin district stood at the left side of the plot and Andabet, Enebise Sar Midir and Borena at the extreme right, contributing to the observed association. The mammal species were found lined up along axis 1, where Lycaon pictus and Reducna redunca were closely associated to Gozamin. The cluster analysis based on the Bray-Curtis single linkage similarity index showed differences and similarities between the mammals species composition recorded in the six districts. P. anubis, C. pygerythrus, S. grimmia, O. oreotragus, G. genetta, P. pardus pardus, H. hyaena, G. sanguinea, H. brucei, P. capensis, H. cristata stood out clearly separated from the rest of them and showed linkage at almost 50% similarity. The highest similarity (at about 96% similarity) was a cluster of four species, i.e., T. sylvaticus, T.strepsiceros, S. scrofa and K. ellipsiprymnus. Non-metric multidimensional scaling also gave clusters of similar districts but not mammal species. Species diversity (H′) ranged from low (1.1) to average (1.9). Anthropogenic impacts were associated with decline in abundance of species and populations. Conservation schemes (nature reserves) need to be launched as soon as possible.
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Tropical forests are becoming increasingly fragmented, threatening the survival of the species that depend on them. Small, isolated forest fragments will lose some of their original species. What is uncertain is how long this process of faunal relaxation will take. We compiled data on birds in five tropical forest fragments in Kakamega Forest, Kenya, of known date of isolation. We then predicted the original and eventual species richness of these fragments and, from this difference, the eventual species losses. Expressing the losses to date as a fraction of eventual losses suggests that faunal relaxation approximates an exponential decay with a half-life of approximately 50 years for fragments of roughly 1000 ha. In other words, in the first 50 years after isolation, tropical forest fragments of this size suffer half of the total number of extinctions that they are likely to experience. This result sets the time scale over which humanity must take conservation action in fragmented tropical forests, may aid efforts to set priorities, and indicates how high the future global extinction rate will be.
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Landsat satellite imagery covering the entire forested portion of the Brazilian Amazon Basin was used to measure, for 1978 and 1988, deforestation, fragmented forest, defined as areas less than 100 square kilometers surrounded by deforestation, and edge effects of 1 kilometer into forest from adjacent areas of deforestation. Tropical deforestation increased from 78,000 square kilometers in 1978 to 230,000 square kilometers in 1988 while tropical forest habitat, severely affected with respect to biological diversity, increased from 208,000 to 588,000 square kilometers. Although this rate of deforestation is lower than previous estimates, the effect on biological diversity is greater.
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Amzonian deforestation rates are used to determine human effects on the global carbon cycle 1-3 and to measure Brazil’s progress in curbing forest impoverishment 1,4,5. But this widely used measure of tropical land use tells only part of the story. Here we present field surveys of wood mills and forest burning across Brazilian Amazonia which show that logging crews severely damage 10,000 to 15,000km2yr-1 offorest that are not included in deforestation mapping programmes. Moreover, we find that surface fires bum additionallarge areas of standing forest, the destruction of which is normally not documented. Forest impoverishment due to such fires mar increase dramatically when severe droughts provoke forest leaf-shedding and greater flammability; our regional water-balance model indicates that an estimated 270,000 km2 of forest became vulnerable to fire in the 1998 dry season. Overall, we find that present estimates of annual deforestation for Brazilian Amazonia capture less than half of the forest area that is impoverished each year, and even less during years of severe drOUght. Both logging and fire increase forest vulnerability to future burning",7 and release forest carbon stocks to the atmosphere, potentially doubling net carbon emissions Ifrom regional land-use during severe El Niflo episodes. If this forest impoverishment is to be controIled, then logging activities I need to be restricted or replaced with low-impact timber harvest techniques, and more effective strategies to prevent accidental forest fires need to be implemented. Pages: 505-508
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The incidence and importance of fire in the Amazon have increased substantially during the past decade, but the effects of this disturbance force are still poorly understood. The forest fire dynamics in two regions of the eastern Amazon were studied. Accidental fires have affected nearly 50 percent of the remaining forests and have caused more deforestation than has intentional clearing in recent years. Forest fires create positive feedbacks in future fire susceptibility, fuel loading, and fire intensity. Unless current land use and fire use practices are changed, fire has the potential to transform large areas of tropical forest into scrub or savanna.
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Recent extinction rates are 100 to 1000 times their pre-human levels in well-known, but taxonomically diverse groups from widely different environments. If all species currently deemed "threatened" become extinct in the next century, then future extinction rates will be 10 times recent rates. Some threatened species will survive the century, but many species not now threatened will succumb. Regions rich in species found only within them (endemics) dominate the global patterns of extinction. Although new technology provides details of habitat losses, estimates of future extinctions are hampered by our limited knowledge of which areas are rich in endemics.
Tropical coral reefs form the most diverse and productive ecosystems in the oceans (Dubinsky, 1990). At higher taxonomic levels (e.g. orders, classes and phyla) reefs are perhaps the most diverse ecosystems in the world and they support a vast, morphologically diverse and colorful array of species. An estimated 4000 species of fishes, approximately 25% of the marine fish species, inhabit coral reefs (McAllister, 1991a). Despite this high biodiversity, coral reefs cover only 0.18% of the world’s oceans (Smith, 1978). The fish fauna of coral reefs is thus two orders of magnitude richer than the average of the fish diversity in the oceans. Coral reefs are important to people since they provide more than half the animal protein in the diets of many tropical countries, considerable employment, and coastal protection against storm waves (McAllister, 1988).
The incidence and importance of fire in the Amazon have increased substantially during the past decade, but the effects of this disturbance force are still poorly understood. The forest fire dynamics in two regions of the eastern Amazon were studied. Accidental fires have affected nearly 50 percent of the remaining forests and have caused more deforestation than has intentional clearing in recent years. Forest fires create positive feedbacks in future fire susceptibility, fuel loading, and fire intensity. Unless current land use and fire use practices are changed, fire has the potential to transform large areas of tropical forest into scrub or savanna.
The world’s tropical forests are being cleared rapidly, and ecologists claim this is causing a massive loss of species. This claim has its critics. Can we predict extinctions from the extent of deforestation? We mapped the percentage of deforestation on the islands of the Philippines and Indonesia and counted the number of bird species found only on these islands. We then used the species-area relationship to calculate the number of species predicted to become globally extinct following deforestation on these islands. Next, we counted the numbers of insular southeast Asian endemic bird species considered threatened—i.e., those having “a high probability of extinction in the wild in the medium-term future”—in the latest summary Red Data Book. The numbers of extinctions predicted from deforestation and the numbers of species actually threatened are strikingly similar. This suggests we can estimate the size of the extinction crisis in once-forested regions from the extent of deforestation. The numbers of extinctions will be large. Without rapid and effective conservation, many of the species endemic to insular southeast Asia will soon be lost.
Conservationists are far from able to assist all species under threat, if only for lack of funding. This places a premium on priorities: how can we support the most species at the least cost? One way is to identify 'biodiversity hotspots' where exceptional concentrations of endemic species are undergoing exceptional loss of habitat. As many as 44% of all species of vascular plants and 35% of all species in four vertebrate groups are confined to 25 hotspots comprising only 1.4% of the land surface of the Earth. This opens the way for a 'silver bullet' strategy on the part of conservation planners, focusing on these hotspots in proportion to their share of the world's species at risk.
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