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Causes and consequences of species extinctions



The five largest mass die-offs in which 50–95% of species were eliminated occurred during the Ordovician [490–443 million years ago (mya)], Devonian (417–354 mya), Permian (299–250 mya), Triassic (251–200 mya), and Cretaceous (146–64 mya) periods. Most recently, human actions especially over the past two centuries have precipitated a global extinction crisis or the ‘‘sixth great extinction wave’’ comparable to the previous five. Increasing human populations over the last 50,000 years or so have left measurable negative footprints on biodiversity.
Copyrighted Material
Causes and Consequences
of Species Extinctions
Navjot S. Sodhi, Barry W. Brook,
and Corey J. A. Bradshaw
1. Introduction
2. Extinction drivers
3. Extinction vulnerability
4. Consequences of extinctions
5. Conclusions
The five largest mass die-offs in which 50– 95% of species
were eliminated occurred during the Ordovician [490–443
million years ago (mya)], Devonian (417–354 mya), Permian
(299–250 mya), Triassic (251–200 mya), and Cretaceous
(146–64 mya) periods. Most recently, human actions espe-
cially over the past two centuries have precipitated a global
extinction crisis or the ‘‘sixth great extinction wave’’ com-
parable to the previous five. Increasing human populations
over the last 50,000 years or so have left measurable
negative footprints on biodiversity.
Allee effects. These factors cause a reduction in the
growth rate of small populations as they decline
(e.g., via reduced survival or reproductive success).
coextinction. Extinction of one species triggers the loss
of another species.
extinction debt. This refers to the extinction of species
or populations long after habitat alteration.
extinction vortex. As populations decline, an insidious
mutual reinforcement occurs among biotic and
abiotic processes driving population size downward
to extinction.
extirpation. This refers to extinction of a population
rather than of an entire species.
invasive species. These are nonindigenous species in-
troduced to areas outside of their natural range that
have become established and have spread.
megafauna. This refers to large-bodied (>44 kg) ani-
mals, commonly (but not exclusively) used to refer
to the large mammal biota of the Pleistocene.
minimum viable population. This is the number of in-
dividuals in a population required to have a speci-
fied probability of persistence over a given period of
In the Americas, charismatic large-bodied animals
(megafauna) such as saber-toothed cats (Smilodon
spp.), mammoths (Mammuthus spp.), and giant ground
sloths (Megalonyx jeffersonii) vanished following hu-
man arrival some 11,000–13,000 years ago. Similar
losses occurred in Australia 45,000 years ago, and in
many oceanic islands within a few hundred years of the
arrival of humans. Classic examples of the loss of is-
land endemics include the dodo (Raphus cucullatus)
from Mauritius, moas (e.g., Dinornis maximus) from
New Zealand, and elephantbirds (Aepyornis maximus)
from Madagascar. Megafaunal collapse during the late
Pleistocene can largely be traced to a variety of negative
human impacts, such as overharvesting, biological in-
vasions, and habitat transformation.
The rate and extent of human-mediated extinctions
are debated, but there is general agreement that ex-
tinction rates have soared over the past few hundred
years, largely as a result of accelerated habitat de-
struction following European colonialism and the sub-
sequent global expansion of the human population
during the twentieth century. Humans are implicated
directly or indirectly in the 100- to 10,000-fold in-
crease in the ‘‘natural’’ or ‘‘background’ extinction
rate that normally occurs as a consequence of gradual
environmental change, newly established competitive
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515 Species Extinctions
interactions (by evolution or invasion), and occasional
chance calamities such as fire, storms, or disease. The
current and future extinction rates are estimated using
a variety of measures such as species–area models and
changes in the World Conservation Union’s (IUCN)
threat categories over time. Based on the global as-
sessment of all known species, some 31, 12, and 20%
of known amphibian, bird, and mammal species, re-
spectively (by far the best-studied of all animal groups),
are currently listed by the IUCN as under threat.
Just how many species are being lost each year is
also hotly debated. Various estimates range from a few
thousand to more than 100,000 species being ex-
tinguished every year, most without ever having been
scientifically described. The large uncertainty comes
mainly through the application of various species–area
relationships that vary substantially among communi-
ties and habitats. Despite substantial prediction error,
it is nevertheless certain that human actions are causing
the structure and function of natural systems to un-
ravel. The past five great extinctions shared some im-
portant commonalities: (1) they caused a catastrophic
loss of global biodiversity; (2) they unfolded rapidly (at
least in the context of evolutionary and geological
time); (3) taxonomically, their impact was not random
(that is, whole groups of related species were lost while
other related groups remained largely unaffected); and
(4) the survivors were often not previously dominant
evolutionary groups. All four of these features are rel-
evant to the current biodiversity crisis. This sixth great
extinction is likely to be most catastrophic in tropical
regions given the high species diversity there (more
than two-thirds of all species) and the large, expanding
human populations that threaten most species there as
The major ‘‘systematic drivers’’ of modern species
loss are changes in land use (habitat loss degradation
and fragmentation), overexploitation, invasive species,
disease, climate change (global warming) connected
to increasing concentration of atmospheric carbon di-
oxide, and increases in nitrogen deposition. Mechan-
isms for prehistoric (caused by humans >200 years
ago) extinctions are likely to have been similar: over-
hunting, introduced predators and diseases, and habi-
tat destruction when early people first arrived in virgin
Some events can instantly eliminate all individuals of
a particular species, such as an asteroid strike, a mas-
sive volcanic eruption, or even a rapid loss of large
areas of unique and critical habitat because of defor-
estation. But ultimately, any phenomena that can cause
mortality rates to exceed reproductive replacement
over a sustained period can cause a species to become
extinct. Such forces may act independently or syner-
gistically, and it may be difficult to identify a single
cause of a particular species extinction event. For in-
stance, habitat loss may cause some extinctions directly
by removing all individuals, but it can also be indirectly
responsible for an extinction by facilitating the estab-
lishment of an invasive species or disease agent, im-
proving access to human hunters, or altering biophys-
ical conditions. As a result, any process that causes a
population to dwindle may ultimately predispose that
population to extinction.
Evidence to date suggests that deforestation is cur-
rently, and is projected to continue to be, the prime
direct and indirect cause of reported extirpations. For
example, it is predicted that up to 21% of Southeast
Asian forest species will be lost by 2100 because of past
and ongoing deforestation. Similar projections exist for
biotas in other regions.
Overexploitation is also an important driver of ex-
tinctions among vertebrates and tends to operate syn-
ergistically with other drivers such as habitat loss. For
example, roads and trails created to allow logging op-
erations to penetrate into virgin forests make previ-
ously remote areas more accessible to human hunters,
who can, in turn, cause the decline and eventual ex-
tirpation of forest species. It is estimated that overex-
ploitation is a major threat to at least one-third of
threatened birds and amphibians, with wildlife cur-
rently extracted from tropical forests at approximately
six times the sustainable rate. In other words, the
quantity, and most likely the diversity, of human prey—
both fisheries and ‘‘bush’’ (wild) meat—are rapidly
Megafauna—those species weighing in the tens to
hundreds of kilograms—are among the most vulnera-
ble to overexploitation. In general, a species’ genera-
tion time (interval from birth to reproductive age) is a
function of body mass (allometry), so larger, longer-
lived, and slower-reproducing animal populations are
generally unable to compensate for high rates of har-
vesting. Because slow-breeding large animals, such as
apes, carnivores (e.g., the lion, Panthera leo), and Af-
rican elephants (Loxodonta africana), are particularly
vulnerable to hunting, the potential for population
recovery in these animals over short time scales is low.
As an example supporting this generality, there is evi-
dence that 12 large vertebrate species have been ex-
tirpated from Vietnam, primarily because of excessive
hunting, within the past 40 years. The Steller’s sea cow
(Hydrodamalis gigas), an aquatic herbivorous mam-
mal that inhabited the Asian coast of the Bering Sea,
is the quintessential example of the rapid demise of a
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516 Conservation Biology
species as a result of overexploitation. Discovered in
1741, it became extinct by 1768 because of overhunt-
ing by sailors, seal hunters, and fur traders. This species
was hunted for food, its skin for making boats, and its
subcutaneous fat for use in oil lamps.
The ecosystem and biological community changes
precipitated by invasive species represent another
leading cause of biodiversity loss. Of 170 extinct spe-
cies for which causes have been identified reliably,
invasive species contributed directly to the demise of
91 (54%). In particular, the rates of extinctions oc-
curring on islands have been greatly elevated by the
introduction of novel predators. Several ecological and
life-history attributes of island species, such as their
naturally constrained geographic range, small popula-
tion sizes, and particular traits (e.g., lack of flight in
birds or lack of thorns in plants) make island biotas
vulnerable to predation from invading species. For
example, the introduction of the brown tree snake
(Boiga irregularis) shortly after World War II wreaked
havoc on the biodiversity of the island of Guam in the
South Pacific. In all likelihood, tree snakes were di-
rectly responsible for the loss of 12 of 18 native bird
species, and they also reduced the populations of other
vertebrates such as flying foxes (Pteropus mariannus),
mainly because of the inability of the island’s native
species to recognize the novel predator as a threat.
Despite an annual expenditure of US$44.6 million for
the management of this problem, tree snakes on Guam
are still not under control, largely because of their
ability to penetrate artificial snake barriers such as
The mosquito Culex quinquefasciatus was inad-
vertently introduced to Hawaii in 1826, and the
disease-causing parasite (Plasmodium relictum) it car-
ries arrived soon after. Since then, avian malaria (in
conjunction with other threats) has been responsible
for the decline and extinction of some 60 species of
endemic forest birds on the Hawaiian Islands. Having
evolved in the absence of the disease, Hawaiian bird
species were generally unable to cope with the debili-
tating effects of the novel parasite. However, more
than 100 years after the establishment of the disease,
some native thrushes (Myadestes spp.) are now show-
ing resistance to the disease. Sadly, many of the re-
maining species, especially forest birds in the family
Drepanididae, are still vulnerable and are now re-
stricted to altitudes where temperatures are below the
thermal tolerance limits of the mosquito vector. Global
warming is predicted to increase the altitudinal distri-
bution of the mosquito, thus spelling doom for disease-
susceptible birds as mosquito-free habitats disappear.
The most feasible method of reducing transmission of
malaria is to reduce or eliminate vector mosquito
populations through chemical treatments and the elim-
ination of larval habitats.
Perhaps one of the most infamous examples of an
invasion catastrophe occurred in the world’s largest
freshwater lake—Lake Victoria in tropical East Africa.
Celebrated for its amazing collection of over 600
endemic haplochromine (i.e., formerly of the genus
Haplochromis) cichlid fishes (Family Cichlidae), the
Lake Victoria cichlid community is perhaps one of the
most rapid, extensive, and recent vertebrate radiations
known. There is also a rich community of endemic
noncichlid fish that inhabit the Lake. In addition to the
threats posed to this unique biota by a rapid rise in
fisheries exploitation, human density, deforestation,
and agriculture during the past century, without doubt
the most devastating effect was the introduction of the
predatory Nile perch (Lates niloticus) in the 1950s.
This voracious predator, which can grow to more than
2 m in length, was introduced from lakes Albert and
Turkana (Uganda and Kenya, respectively) to com-
pensate for depleting commercial fisheries in Lake
Victoria. Although the Nile perch population remained
relatively low for several decades after its introduc-
tion, an eventual population explosion in the 1980s
caused the devastating direct or indirect extinction of
200–400 cichlid species endemic to the Lake as well as
the extinction of several noncichlid fish species. Al-
though many other threats likely contributed to the
observed extinctions, including direct overexploitation
and eutrophication from agriculture and deforestation
leading to a change in the algal plankton community,
there are few other contemporary examples of such a
rapid and massive extinction event involving a single
group of closely related species.
Human-mediated climate change represents a po-
tentially disastrous sleeping giant in terms of future
biodiversity losses. Climate warming can affect species
in five principal ways: (1) alterations of species densi-
ties (including altered community composition and
structure); (2) range shifts, either poleward or upward
in elevation; (3) behavioral changes, such as the phe-
nology (seasonal timing of life cycle events) of migra-
tion, breeding, and flowering; (4) changes in mor-
phology, such as body size; and (5) reduction in genetic
diversity that leads to inbreeding depression. A related
threat for island and coastal biotas is the predicted loss
of habitat via inundation by rising sea levels. Although
large fluctuations in climate have occurred regularly
throughout Earth’s history, the implications of an-
thropogenic global warming for contemporary biodi-
versity are particularly pessimistic because of the rate
of change and previous heavy modification of land-
scapes by humans. Good empirical evidence for some
of these effects is rare, and speculations abound, but
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517 Species Extinctions
there are already many local or regional examples
and model-based predictions that support the view
that rapid climate change, acting in concert with other
drivers of species loss and habitat degradation, will be
one of the most pressing conservation issues global
biodiversity faces over the coming centuries.
One glimpse of a possible future crisis comes
from the highland forests of Monterverde (Costa Rica),
where 40% (20 of 50) of frog and toad species dis-
appeared following synchronous population crashes in
1987, with most crashes linked to a rapid progressive
warming and drying of the local climate. The locally
endemic golden toad (Bufo periglenes) was one of the
high-profile casualties in this area. It has been sug-
gested that climate warming resulted in a retreat of the
clouds and a drying of the mountain habitats, making
amphibians more susceptible to fungal and parasite
outbreaks. Indeed, the pathogenic chytrid fungus Ba-
trachochytrium dendrobatidis, which grows on am-
phibian skin and increases mortality rates, has been
implicated in the loss of harlequin frogs (Atelopus spp.)
in Central and South America and reductions in
other amphibian populations elsewhere. It is hypoth-
esized that warm and dry conditions may stress am-
phibians and make them more vulnerable to the fungal
Irrespective of the reason for a population’s decline
from a large to small population size, unusual (and
often random and detrimental) events assume promi-
nence at low abundances. For instance, although
competition among individuals is reduced at low den-
sities and can induce a population rebound, a coun-
tervailing phenomenon known as the ‘‘Allee effect’’ can
act to draw populations toward extinction by (for in-
stance) disrupting behavioral patterns that depend on
numbers (e.g., herd defense against predators) or by
genetic threats such as inbreeding depression. Small
populations, dominated by chance events and Allee
effects, are often considered to have dipped below their
‘‘minimum viable population’’ size. Thus, once a major
population decline has occurred (from habitat loss,
overexploitation, or in response to many other possible
stressors), an ‘‘extinction vortex’’ of positive feed-
back loops can doom species to extinction, even if the
original threats have been alleviated. Further, many
species may take decades to perish following habitat
degradation. Although some species may withstand
the initial shock of land clearing, factors such as the
lack of food resources, breeding sites, and dispersers
may make populations unviable, and they eventually
succumb to extinction. This phenomenon evokes the
concept of ‘‘living-dead’’ species, or those ‘‘committed
to extinction.’’ The eventual loss of such species is
referred to as the ‘‘extinction debt’’ caused by past
habitat loss. For example, even if net deforestation
rates can be reduced or even halted, the extinction debt
of remnant and secondary forest patches will see the
extinction of countless remaining species over this
Certain life-history, behavioral, morphological, and
physiological characteristics appear to make some spe-
cies more susceptible than others to the extinction
drivers described above. In general, large-sized species
with a restricted distribution that demonstrate habitat
specialization tend to be at greater risk of extinction
from human agency than others within their respective
taxa (e.g., Javan rhinoceros, Rhinoceros sondaicus),
especially to processes such as rapid habitat loss.
Because of their high habitat specificity and/or low
population densities, rare species may be more prone to
extinction than common species. The size of a species’
range is also a major determinant of its extinction
proneness. Small ranges may make species more vul-
nerable to stochastic perturbations, even if local abun-
dance is high; for example, proportionally more
passerines (perching birds) with relatively small geo-
graphic ranges in the Americas are at risk of extinction
than their more widely distributed counterparts. Such
trends are worrisome because those species with
shrinking ranges as a result of adverse human activities
become particularly vulnerable to other drivers such as
climate change. Habitat loss also reduces the patch
sizes necessary for species requiring large home ranges,
making them vulnerable to extinction from a loss of
subpopulation connectedness, reduced dispersal ca-
pacity, and the ensuing lower population viability.
Larger-bodied vertebrates are considered to be more
extinction-prone than smaller-bodied ones when the
threatening process unfolds rapidly or intensely. In-
deed, threatened mammals are an order of magnitude
heavier than nonthreatened ones. A common expla-
nation for this trend is that body size is inversely cor-
related with population size, making large-bodied an-
imals less abundant and more vulnerable to chronic
environmental perturbations (while being buffered
against short-term environmental fluctuations). The
extinction proneness of large-bodied animals to human
activities is further enhanced because of other corre-
lated traits, such as their requirement of large area,
greater food intake, high habitat specificity, and lower
reproductive rate.
Large species can also be more vulnerable to human
persecution such as hunting, whereas smaller species
are generally more vulnerable to habitat loss. It is im-
portant, however, to be cautious when constructing
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518 Conservation Biology
generalized rules regarding the role of body size in the
extinction process. Because they have a slower repro-
ductive rate, larger parrots are more vulnerable to
overexploitation than smaller finches, despite fewer
numbers of the former being captured for the pet trade.
However, some smaller species (e.g., white-eyes, Zos-
terops spp.) with small population sizes are also vul-
nerable to extinction because of heavy harvest rates for
the pet trade, suggesting that only when the threatening
processes are approximately equivalent will the larger
of two species being compared demonstrate a higher
risk of extinction. In addition to body size, other
morphological characteristics affect extinction prone-
ness. For instance, large investment in secondary sexual
characteristics may render highly dimorphic species
less adaptable in a changing environment or more at-
tractive to specimen or pet-trade collectors.
When an environment is altered abruptly or sys-
tematically at a rate above normal background change,
or beyond the capacity of adaptation via natural se-
lection, specialist species with narrow ecological niches
often bear the brunt of progressively unfavorable
conditions such habitat loss and degradation. For in-
stance, highly specialized forest-dependent taxa are
acutely vulnerable to extinction following deforesta-
tion and forest fragmentation. Possible mechanisms
include reductions in breeding and feeding sites, in-
creased predation, elevated soil erosion and nutrient
loss, dispersal limitation, enhanced edge effects, and
other stressors. Conversely, non-forest-dependent spe-
cies or those that prefer open habitats are often better
able to persist in disturbed landscapes and may even be
favored by having fewer competitors or expanded
ranges following deforestation. It is important to be
aware that in relatively stable systems, evolution en-
genders the speciation of taxa that occupy all available
niches so both specialist and generalist species can co-
exist. As a result, the rapid pace of habitat and climate
change renders specialization a modern ‘‘curse’’ in
evolutionary terms.
Foraging specialization is one mechanism that can
compromise a species’ ability to persist in altered
habitats. Many studies have shown that frugivorous
and insectivorous birds are more extinction-prone than
other avian feeding guilds, with the lack of year-round
access to fruiting plants in fragmented forests being the
culprit for the former. A number of hypotheses have
been proposed to explain the disappearance of insec-
tivorous birds from deforested or fragmented areas.
First, deforestation may impoverish the insect fauna
and reduce selected insectivore microhabitats (e.g.,
dead leaves). Second, insectivores may be poor dis-
persers and have near-ground nesting habits, the latter
trait making them more vulnerable to nest predators
penetrating smaller forest fragments. Absence of some
insectivorous bird species from small fragments may
not be related to food scarcity; rather, it may result
from their poorer dispersal abilities. The ability to
disperse in birds and insects depends on morphological
characteristics such as wing loading, and physiological
restrictions such as intolerance to sunlight when mov-
ing within the nonforested matrix landscape separat-
ing fragments. As a result, poor dispersal ability may
make certain species vulnerable to extinction because
they cannot readily supplement sink habitats (habi-
tats in which populations cannot replace themselves),
supporting otherwise unviable subpopulations, or
colonize new areas. Because of poor dispersal abil-
ity, patchy distributions, and generally low popula-
tion densities, the genetic diversity of species in
fragmented landscapes may be difficult to maintain,
with the resulting inbreeding depression further re-
ducing population size toward extinction. However,
clear and quantitative demonstrations of the role of
life-history traits in the extinction process of biotas are
still rare.
The extinction of certain species such as large preda-
tors and pollinators may have more devastating eco-
logical consequences than the extinction of others.
Ironically, avian vulnerability to predation is often
exacerbated when certain large predatory species be-
come rarer in tropical communities. For example, al-
though large cats such as jaguars (Panthera onca)do
not prey on small birds directly, they exert a limiting
force on smaller predators such as medium-sized and
small mammals (mesopredators), which become more
abundant with the former species’ decline. The cor-
ollary is that abundant mesopredators inflict an above-
average predation rate on the eggs and nestlings of
small birds. Although this ‘mesopredator-release’’
hypothesis has been applied largely to mammals (e.g.,
Australian dingoes, Canis lupus, suppressing foxes and
cats; coyotes in California controlling cat abundance),
the loss of large predatory birds such as the harpy eagle
(Harpia harpyja) may have similar ecosystem effects.
Similar mesopredator release has been demonstrated
for the first time in the marine environment, where the
overexploitation of large pelagic sharks resulted in an
increase in rays and skates that eventually suppressed
commercially important scallop populations. Likewise,
does the disappearance of a competitor result in the
niche expansion and higher densities of subordinate
species? This phenomenon has been observed between
unrelated taxa—the extinction of insectivorous birds
from scrub forests of West Indian islands correlated
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519 Species Extinctions
with the subsequent higher biomass of competing
Anolis lizards.
Conservation biologists have traditionally focused
on the study of the independent declines, extirpations,
or extinctions of individual species while paying rela-
tively less attention to the possible cascading effects of
species coextinctions (e.g., hosts and their parasites).
However, it is likely that many coextinctions between
interdependent taxa have occurred, but most have gone
unnoticed in these relatively understudied systems. For
example, an extinct feather louse (Columbicola ex-
tinctus) was discovered in 1937, 23 years after likely
coextinction with its host passenger pigeon (Ectopistes
migratorius). Ecological processes disrupted by ex-
tinction or species decline may also lead to cascading
and catastrophic coextinctions. Frugivorous animals
and fruiting plants on which they depend have a key
interaction linking plant reproduction and dispersal
with animal nutrition. Thus, the two interdependent
taxa are placed in jeopardy by habitat degradation.
Many trees produce large, lipid-rich fruits adapted for
animal dispersal, so the demise of avian frugivores may
have serious consequences for forest regeneration, even
if the initial drivers of habitat loss and degradation are
Essential ecosystem functions provided by forest
invertebrates are also highly susceptible when species
are lost after habitat loss and degradation. Acting as
keystone species in Southeast Asian rainforests, figs
rely on tiny (1–2 mm) species-specific wasps for their
pollination. Some fig wasps may have limited dispersal
ability, suggesting that forest disturbance can reduce
wasp densities and, by proxy, the figs that they polli-
nate. Similarly, dung beetles are essential components
of ecosystem function because they contribute heavily
to nutrient-recycling processes, seed dispersal, and the
reduction of disease risk associated with dung accu-
mulation. In Venezuela, heavier dung beetles were
more extinction-prone than lighter species on artifi-
cially created forested islands, which predicts particu-
larly dire ecosystem functional loss given the former
group’s greater capacity to dispose of dung.
Almost all flowering plants in tropical rainforests
are pollinated by animals, and an estimated one-third
of the human diet in tropical countries is derived from
insect-pollinated plants. Therefore, a decline of forest-
dwelling pollinators impedes plant reproduction not
only in forests but also in neighboring agricultural
areas visited by these species. Lowland coffee (Coffea
canephora) is an important tropical cash crop, and it
depends on bees for cross-pollination. A study in Costa
Rica found that forest bees increased coffee yield by
20% in fields within 1 km of the forest edge. Between
2000 and 2003, the pollination services provided by
forest bees were worth US$60,000 to a 1100-ha farm.
A forest patch as small as 20 ha located near farms
can increase coffee yield and thus bring large eco-
nomic benefits to the farmers. Such findings illustrate
the imperative of preserving native forests near agro-
forestry systems to facilitate the travel by forest-
dependent pollinating insects.
Although extinctions are a normal part of evolution,
human modifications to the planet in the last few
centuries, and perhaps even millennia, have greatly
accelerated the rate at which extinctions occur. Habitat
loss remains the main driver of extinctions, but it may
act synergistically with other drivers such as over-
harvesting and pollution, and, in the future, climate
change. Large-bodied species, rare species, and habitat
specialists are particularly prone to extinction as a re-
sult of rapid human modifications of the planet. Ex-
tinctions can disrupt vital ecological processes such as
pollination and seed dispersal, leading to cascading
losses, ecosystem collapse, and a higher extinction rate
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ogy 16: 584–586. This work provides a quantitative
overview of the extent of threat faced by birds and
mammals from direct exploitation by people.
Sekercioglu, Cagan H., Gretchen C. Daily, and Paul R. Ehr-
lich. 2004. Ecosystem consequences of bird declines.
Proceedings of the National Academy of Sciences U.S.A.
101: 18042–18047. This article provides a framework for
assessing the loss of ecosystem functions caused by avian
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... Conservation of biological diversity includes these plant species, including Safed Musli, but due to over-exploitation, these plant species are on the verge of extinction. These plant species are also used for carrying out different scientific and biological experiments to use them in pharmaceutical drugs, but the population puts a severe risk to the natural resources, including flora fauna and endangered plant species [60]. ...
... Excessive developmental activities have also destroyed habitats. The growth of development comprises many activities, such as roads, railway lines, dams, mines, and human settlements, which inconsequentially disturb the whole ecosystem and thus affect the normal growth of endangered plant species [60]. The cumulative result of climate change, natural habitats, and population growth development activities affect the overall percentage of flora and fauna, and plant species in the country. ...
... The cumulative result of climate change, natural habitats, and population growth development activities affect the overall percentage of flora and fauna, and plant species in the country. These plant species are at risk because of a lack of effective regulatory control mechanisms, which makes the issue of plant species more complex [60]. ...
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The present review paper is an attempt to examine and provide an overview of the various conservation strategies and regulatory framework to protect endangered plants, including Chlorophytum tuberosum, popularly known as Safed Musli in the local language. C. tuberosum belongs to the family Liliaceae and is being used in the indigenous systems of medicine as a galactagogue, aphrodisiac, antitumor, immunomodulatory, antidiabetic, analgesic, anti-inflammatory, hypolipidemic, anti-ageing, antimicrobial, etc. This plant has great medicinal and commercial value and is part of the Biological Diversity Act, but due to a lack of effective conservation, it is on the verge of extinction because of natural and manmade reasons, such as loss of habitat, climate change, pollution, excessive harvesting, etc. The most valuable medicinal plants have great importance; hence, many conservation techniques are being employed to protect them. In furtherance to the conservation of such plant species, strategic efforts, in the form of laws and policies, are laid; however, existing legislative mechanisms and policy parameters are not sufficient to overcome the challenges of conservation of such plant species, including Safed Musli, hence, this plant has been considered as a critically endangered plant in India. It is pertinent to note that we do not have specific legislation enacted for the protection of plant species; however, efforts are being made to conserve it under various laws, such as the Forest Conservation Act, Biological Diversity Act 2002, and many other allied legislations. This basic legislation of the Biological Diversity Act also lacks focal attention on the conservation of endangered plant species. Moreover, decentralization of power and actual community participation in conservation practices are also missing. A cumulative effect of both scientific measures and legal mechanisms supported by community participation may produce better results in the conservation of plant species, including Safed Musli. The protection of rich sources and biological diversity is not being taken as seriously as it ought to be, hence, it is necessary to improve awareness and public participation in conservation techniques with effective legislation for the conservation of highly endangered plant species.
... Deforestation is the current and projected primary direct and indirect cause of species extinction. It is predicted that up to 21% of Southeast Asian forest species will disappear by the year 2100 due to previous and present deforestation (Sodhi et al. 2009). Furthermore, climate change can have a significant impact on ecological and biotic elements that influence the global distribution of habitats and species (Dar et al. 2019), such as a shift in the plant-pollinator relationship through phenological changes and regeneration failure due to stress on species or their native environments (Parmesan 2006;Reyer et al. 2013). ...
... Physiology, demography, dispersion, interspecific interactions, adaptation, and alteration of environmental factors are crucial processes influencing biodiversity to respond to global change (Urban et al. 2016). Some extinctions may happen as a direct result of habitat loss by removing all individuals, or they may happen indirectly as a result of aiding the spread of a disease or invading species, making it easier for humans to hunt them, or changing biophysical circumstances (Sodhi et al. 2009). Humancaused climate change, characterized by unprecedented variations in temperature and precipitation regimes, poses an additional threat to biodiversity and hastens climate fluctuations on ecosystems, which significantly impact conservation goals, resulting in the waste of vital and scarce conservation inputs (Millar et al. 2007). ...
Chilika lagoon is the first Ramsar site in India located along the East Coast. Prediction of the eutrophication of such ecosystems is a key approach for a sustainable management perspective as it helps to formulate a management action plan. In the present study a data-driven modeling approach, an Artificial neural network (ANN) was used to predict eutrophication in the Chilika lagoon. Back-propagation neural network model was used to relate the major parameters which influence the eutrophication indicators such as Total nitrogen (TN), Total phosphorus (TP), Secchi disc depth (SD), dissolved oxygen (DO), Biological oxygen demand (BOD), pH, Water Temperature (WT), Turbidity (TURB). The model evidenced an acceptable level of prediction when compared with the results of the field observations. This model's most important determinant variables were those with a high Random Forest (RF) model permutation relevance ranking, which reduced the network's structure and led to a more accurate and effective process. It demonstrated a high agreement between BOD and turbidity. As per the TLI estimation, the Chilika lagoon was observed to maintain an oligotrophic condition. However, there was a trophic switchover between the seasons and sectors. The study evidenced that the ANN was able to predict the indicators with reasonable accuracy which could be proved as a valuable tool for the Chilika lagoon. This approach can be considered while the formulation of the sustainable management and conservation action plan for Chilika and other similar aquatic ecosystems around the globe.
... Deforestation is the current and projected primary direct and indirect cause of species extinction. It is predicted that up to 21% of Southeast Asian forest species will disappear by the year 2100 due to previous and present deforestation (Sodhi et al. 2009). Furthermore, climate change can have a significant impact on ecological and biotic elements that influence the global distribution of habitats and species (Dar et al. 2019), such as a shift in the plant-pollinator relationship through phenological changes and regeneration failure due to stress on species or their native environments (Parmesan 2006;Reyer et al. 2013). ...
... Physiology, demography, dispersion, interspecific interactions, adaptation, and alteration of environmental factors are crucial processes influencing biodiversity to respond to global change (Urban et al. 2016). Some extinctions may happen as a direct result of habitat loss by removing all individuals, or they may happen indirectly as a result of aiding the spread of a disease or invading species, making it easier for humans to hunt them, or changing biophysical circumstances (Sodhi et al. 2009). Humancaused climate change, characterized by unprecedented variations in temperature and precipitation regimes, poses an additional threat to biodiversity and hastens climate fluctuations on ecosystems, which significantly impact conservation goals, resulting in the waste of vital and scarce conservation inputs (Millar et al. 2007). ...
In this chapter, stacked species distribution models derived from maximum entropy and random forest models are applied on tree species distribution data from Eswatini to estimate and map taxonomic and phylogenetic diversity and endemism using six indices: species richness (SR), taxonomic weighted endemism (WE), corrected taxonomic weighted endemism (CWE), phylogenetic diversity (PD), weighted phylogenetic endemism (WPE) and corrected weighted phylogenetic endemism (CWPE). In addition, hotspots were identified by mapping the 95% percentile of the values from each index.
... Such a positive relationship suggests that the loss of species can impact functional composition of species-poorer communities. Ecosystem functioning is often assumed to rely mostly on common species (widely distributed and abundant species), and not on rare species (narrowly distributed and of low abundance) that are more prone to extinction [60]. Thus, one could speculate that the loss of rare species would not affect ecosystem functioning. ...
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Biodiversity promotes the functioning of ecosystems, and functional redundancy safeguards this functioning against environmental changes. However, what drives functional redundancy remains unclear. We analyzed taxonomic diversity, functional diversity (richness and β-diversity) and functional redundancy patterns of British butterflies. We explored the effect of temperature and landscape-related variables on richness and redundancy using generalized additive models, and on β-diversity using generalized dissimilarity models. The species richness-functional richness relationship was saturating, indicating functional redundancy in species-rich communities. Assemblages did not deviate from random expectations regarding functional richness. Temperature exerted a significant effect on all diversity aspects and on redundancy, with the latter relationship being unimodal. Landscape-related variables played a role in driving observed patterns. Although taxonomic and functional β-diversity were highly congruent, the model of taxonomic β-diversity explained more deviance than the model of functional β-diversity did. Species-rich butterfly assemblages exhibited functional redundancy. Climate- and landscape-related variables emerged as significant drivers of diversity and redundancy. Τaxonomic β-diversity was more strongly associated with the environmental gradient, while functional β-diversity was driven more strongly by stochasticity. Temperature promoted species richness and β-diversity, but warmer areas exhibited lower levels of functional redundancy. This might be related to the land uses prevailing in warmer areas (e.g., agricultural intensification).
... The ongoing loss and conversion of vast stretches of natural habitats across the world's lands; the 48 overexploitation of wild plants and animals on land and in the oceans; pollution, climate change, and the 49 resultant degradation of ecosystem services have triggered a planetary environmental crisis and mass 50 extinction of species (Dasgupta 2021). In the earlier mass extinctions, with the first one occurring between 51 490 to 443 million years ago, the earth lost 50 to 95% of its extant species (Sodhi et al. 2009). In the next 52 few years, 25% of the estimated species on the planet face extinction. ...
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Since the industrial revolution, the predominant model of economic development hasinvolved economies of scale and unsustainable exploitation of natural resources,leading to environmental degradation and the ongoing mass extinction of species. The environmental impacts of this development-for(the sake of)-development model led to biodiversity conservation efforts that can be described as conservation-for (the sake of)-conservation approach involving protected areas maintained free of humans. This approach subsequently expanded to include development-for-conservation efforts that integrated local community welfare into conservation programs. These conservation approaches helped make socio-ecological gains, but have failed to address planetary environmental degradation. Here, we outline a development approach for the earth’s last-remaining biodiversity rich areas, focusing on economies of value rather than scale, and relying on conservation of biodiversity and sustainable use of ecosystem services. This conservation-for-development model is an attempt to bring humanity and nature closer, and move away from nature–people dualism that has characterized economic development and biodiversity conservation so far.
... Larger organisms tend to be more affected by environmental impacts than smaller organisms (Cardillo et al., 2005;Sodhi et al., 2009). ...
Land-use and land-cover transitions can affect biodiversity and ecosystem functioning in a myriad of ways, including how energy is transferred within food-webs. Size spectra (i.e. relationships between body size and biomass or abundance) provide a means to assess how food-webs respond to environmental stressors by depicting how energy is transferred from small to larger organisms. Here, we investigated changes in the size spectrum of aquatic macroinvertebrates along a broad land-use intensification gradient (from Atlantic Forest to mechanized agriculture) in 30 Brazilian streams. We expected to find a steeper size spectrum slope and lower total biomass in more disturbed streams due to higher energetic expenditure in physiologically stressful conditions, which has a disproportionate impact on large individuals. As expected, we found that more disturbed streams had fewer small organisms than pristine forest streams, but, surprisingly, they had shallower size spectra slopes, which indicates that energy might be transferred more efficiently in disturbed streams. Disturbed streams were also less taxonomically diverse, suggesting that the potentially higher energy transfer in these webs might be channeled via a few efficient trophic links. However, because total biomass was higher in pristine streams, these sites still supported a greater number of larger organisms and longer food chains (i.e. larger size range). Our results indicate that land-use intensification decreases ecosystem stability and enhances vulnerability to population extinctions by reducing the possible energetic pathways while enhancing efficiency between the remaining food-web linkages. Our study represents a step forward in understanding how land-use intensification affects trophic interactions and ecosystem functioning in aquatic systems.
... No captures of NS adults or juveniles occurred in any stocked streams after 2014. Sodhi et al. (2009) summarized drivers leading to the extinction of rare species (or extirpations of small populations): changes in land use (habitat loss, degradation, or fragmentation), over exploitation, invasive species, disease, climate change, pollution levels, and catastrophic events. Any or a combination of the italicized factors in the previous sentence occurred in LTC and could have contributed to the extirpation of NS there. ...
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The Northern Sunfish (Lepomis peltastes Cope, 1870) is threatened in New York state, USA, but this was not the case before 1940 when the NY Biological Survey documented the species at scattered, specialized habitats in six watersheds in the central and western parts of the state. After 1940 the historic populations could not be detected, but a new population was discovered in 1974 in lower Tonawanda Creek and the nearby Erie Canal. Northern Sunfish, and a few of their hybrids with other Lepomis species, were caught at these locations during irregular sampling through 2009, but no Northern Sunfish were caught after 2009. The objectives of our study were to: (1) Determine the extent of Northern Sunfish hybridization with other Lepomis species, and (2) Evaluate how well identifications of Lepomis species and their hybrids agreed among field keys, morphometric measurements and meristic counts, and genetic methods. In 2013, we collected Northern Sunfish (descended from fish captured in lower Tonawanda Creek from 2006-2009) from NY State Department of Environmental Conservation rearing ponds, plus wild Green Sunfish (L. cyanellus Rafinesque, 1819), Pumpkinseed (L. gibbosus Linnaeus, 1758), Bluegill (L. macrochirus Rafinesque, 1819), and suspected Lepomis hybrids from lower Tonawanda Creek. Ultimately, 91 fish were identified using field keys, morphometric-meristic analysis, and mtDNA and nuclear DNA analysis. Assuming genetic analysis provided accurate identification, we found 7 Bluegill × Northern Sunfish, 8 Bluegill × Pumpkinseed, 13 Bluegill × Green Sunfish, and 3 Green Sunfish × Pumpkinseed hybrids in our sample (female parent listed second in these crosses). Keyed and morphometric-meristic identifications did not differ in accuracy and averaged 81% of genetic identification accuracy. After Northern Sunfish stocking (not in our study area) and sampling from 2008 to 2018 in several watersheds with appropriate habitat and no recaptures after 2014, we conclude that the Northern Sunfish is extirpated in western New York state.
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Abstract—There are currently two unanswered questions in horned dinosaur evolution. First, how could western North America support such a high diversity of ecologically similar, large-bodied dinosaur species in the late Campanian? Second, why was the trophic network of western North American dinosaurs restructured during this time, reducing the apparent pattern of high dinosaur endemism, when there is no obvious evidence for a perturbation to the physical environment (ca. 76 Ma)? In order to address these two questions, this investigation examines recently published ceratopsid dinosaur phylogenies, which take into account new data from New Mexico, for their phylogeographic signal, and finds that ceratopsid dinosaur species demonstrating mutual extinction (i.e., temporally clustered last appearance data or LADs) were significantly more closely related and similar in paleobiogeographic distribution than expected due to chance. Moreover, mutual extinction peaked immediately after the attainment of maximum standing diversity of the ceratopsid dinosaurs, and the timing of mutual extinction events was normally distributed about this peak. As the original Red Queen hypothesis postulated that any two taxa drawn at random from a phylogenetic tree exhibit an equal probability of extinction, this study reframes this hypothesis, which is nonetheless associated with the standard log-linear survivorship curve, as the “Red Queen’s axe” to denote the non-random rather than random pruning of a phylogenetic tree by biotic competition. A Shannon entropy-based test finds that mutual extinction events are not “significantly concentrated in time,” which is a requisite of the alternative Turnover-Pulse hypothesis. Accordingly, this investigation reshapes our understanding of the role of biotic competition in generating macroevolutionary patterns by highlighting yet another example of the “tragedy of the commons.”
In June-July 2020, a study of the Ladoga ringed seal haul-out use pattern was carried out on the islands of the Valaam Archipelago , Lake Ladoga, in NorthWestern Russia, where the subspecies' largest summer haul-outs are observed annually. Trail cameras automatically collected imagery every 10 min, 24 h a day. Over 22,000 images were collected with 198 camera-days, and seals were present in over 20% of them. The total number of seals photographed by all cameras per day ranged from 2 to 149 individuals. The seals typically began approaching the haul-out sites at night, with abundance peaking between 8:00 a.m. and 12:00 p.m. local time, and then gradually declining during the afternoon hours. Changes in air temperature, wind direction, wind speed, and wave height affected the likelihood of seals remaining at the haul-outs. Major disturbances, such as motorboats or helicopters, drove the seals to leave their resting areas, and during the morning and evening hours resulted in at least 6-h disruption of haul-out dynamics. This research presents a reliable, cost-effective approach for monitoring Ladoga ringed seal at coastal haul-outs which has direct implications to addressing population conservation needs.
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Fish introduction into fishless high-altitude lakes has detrimental effects on biodiversity. Removal of alien fish through intensive fishing is cost-intensive and difficult to achieve in productive lakes. Lake Sulzkarsee is the only lake in the National Park Gesäuse, Austria, and was an important breeding site for amphibians until the lake was stocked with fish in the late 1970s. Salmonids were eradicated in 2005, but the lake remained degraded by the introduced minnows (Phoxinus sp.). In 2018, the lake was drained through a siphon pipe and then by pumping out water with dirt water pumps. The deepest part was treated with slaked lime, but several hundred adult minnows survived in sediment crevices and reproduced in the following season. After drainage, the phytoplankton biomass increased. Indicator species, such as Daphnia longispina and amphibians, showed signs of recovery, but they went back to an impacted state when minnows recovered after the failed eradication attempt. Purse seines proved to be the most efficient gear to catch minnows. These results indicate that deep mountain lakes are difficult to drain efficiently. Sediment treatment is required to eliminate all fish.
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Can economic forces be harnessed for biodiversity conservation? The answer hinges on characterizing the value of nature, a tricky business from biophysical, socioeconomic, and ethical perspectives. Although the societal benefits of native ecosystems are clearly immense, they remain largely unquantified for all but a few services. Here, we estimate the value of tropical forest in supplying pollination services to agriculture. We focus on coffee because it is one of the world's most valuable export commodities and is grown in many of the world's most biodiverse regions. Using pollination experiments along replicated distance gradients, we found that forest-based pollinators increased coffee yields by 20% within ≈1 km of forest. Pollination also improved coffee quality near forest by reducing the frequency of “peaberries” (i.e., small misshapen seeds) by 27%. During 2000–2003, pollination services from two forest fragments (46 and 111 hectares) translated into ≈$60,000 (U.S.) per year for one Costa Rican farm. This value is commensurate with expected revenues from competing land uses and far exceeds current conservation incentive payments. Conservation investments in human-dominated landscapes can therefore yield double benefits: for biodiversity and agriculture. • bees • ecosystem service • landscape • pollination
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To assess the coextinction of species (the loss of a species upon the loss of another), we present a probabilistic model, scaled with empirical data. The model examines the relationship between coextinction levels (proportion of species extinct) of affiliates and their hosts across a wide range of coevolved interspecific systems: pollinating Ficus wasps and Ficus, parasites and their hosts, butterflies and their larval host plants, and ant butterflies and their host ants. Applying a nomographic method based on mean host specificity (number of host species per affiliate species), we estimate that 6300 affiliate species are “coendangered” with host species currently listed as endangered. Current extinction estimates need to be recalibrated by taking species coextinctions into account.
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As the Earth warms, many species are likely to disappear, often because of changing disease dynamics. Here we show that a recent mass extinction associated with pathogen outbreaks is tied to global warming. Seventeen years ago, in the mountains of Costa Rica, the Monteverde harlequin frog (Atelopus sp.) vanished along with the golden toad (Bufo periglenes). An estimated 67% of the 110 or so species of Atelopus, which are endemic to the American tropics, have met the same fate, and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis) is implicated. Analysing the timing of losses in relation to changes in sea surface and air temperatures, we conclude with 'very high confidence' (> 99%, following the Intergovernmental Panel on Climate Change, IPCC) that large-scale warming is a key factor in the disappearances. We propose that temperatures at many highland localities are shifting towards the growth optimum of Batrachochytrium, thus encouraging outbreaks. With climate change promoting infectious disease and eroding biodiversity, the urgency of reducing greenhouse-gas concentrations is now undeniable.
This work provides a quantitative overview of the extent of threat faced by birds and mammals from direct exploitation by people
  • Alison M Rosser
  • Sue A Manika
Rosser, Alison M., and Sue A. Manika. 2002. Overexploitation and species extinctions. Conservation Biol­ ogy 16: 584-586. This work provides a quantitative overview of the extent of threat faced by birds and mammals from direct exploitation by people.
Extinction by numbers The article summarizes the likely extent of biodiversity losses as a result of human activities
  • Conservation Biology Pimm
  • L Stuart
  • Peter Raven
Conservation Biology Pimm, Stuart L., and Peter Raven. 2000. Extinction by numbers. Nature 403: 843–845. The article summarizes the likely extent of biodiversity losses as a result of human activities.
The article summarizes the likely extent of biodiversity losses as a result of human activities
  • Stuart L Pimm
  • Peter Raven
Pimm, Stuart L., and Peter Raven. 2000. Extinction by numbers. Nature 403: 843-845. The article summarizes the likely extent of biodiversity losses as a result of human activities.
This work shows how the loss of ecosystem services can affect pol­ lination of commercial crops
  • Taylor H Ricketts
  • C Gretchen
  • Paul R Daily
  • C D Ehrlich
  • Michener
Ricketts, Taylor H., Gretchen C. Daily, Paul R. Ehrlich, and C. D. Michener. 2004. Economic value of tropical forest to coffee production. Proceedings of the National Acad­ emy of Sciences U.S.A. 34: 12579-12582. This work shows how the loss of ecosystem services can affect pol­ lination of commercial crops.