THE SIXTH MASS EXTINCTION Human Accountability for Species
Becoming Endangered and Extinct Erica Hardin 4-26-2012
Environmental Biology 1
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INTRODUCTION Since modern humans have existed, the rate of
species extinction has abruptly increased. This is known as the
sixth mass extinction event, because it far surpasses the natural
evolutionary extinction process, called background extinction, in
which species die out becoming slowly replaced by descendant
species. The rapid loss of species today is estimated by some
experts to be up to 1,000 times higher than the natural extinction
rate, while other estimates are even 1,000 times higher than those
estimates! In 1993, biologist E.O. Wilson estimated that 30,000
species become extinct each year. 2
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HUMAN POPULATION Around 0 A.D., there were about 300 million
people on Earth. There are currently about 6.7 billion people on
Earth. The human population has tripled twice in only the past 200
years. With a net gain of about 200,000 people per day, the
population densities range from 0.04 to 27,300 people/square
kilometer on the 150 million square km surface of the planet. This
gives us a current world-averaged density of about 40 people per
every km 2. Natural carrying capacity for humans, when compared to
the carrying capacity of other species, should be around 15 to 150
million people. That would mean a density of 1 person/km 2 or less.
Human population is up to 400 times greater than natural carrying
capacity. 3
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4 EARLY EXTINCTIONS IN HUMAN HISTORY Contrary to popular
belief, human-caused extinctions are not a recent development. Some
scientists even believe that our ancestors, Homo erectus may have
started the cascade of extinctions, the sixth mass extinction.
Neanderthals are believed to be the first extinction caused by
humans. These hominids lived in Europe and Asia from 120,000 years
ago until about 35,000 years ago. They were driven to extinction by
competition with modern humans, Homo sapiens. They had a burly
stature and their brain size was equal to or larger than the
average human brain. They were the first to systematically bury
their dead. There has been no evidence to suggest that genetic
material was exchanged between our two species, making Neanderthals
only humans closest cousin. Megafauna extinctions occurred in the
late Pleistocene and in the Holocene upon arrival of humans to
Australia, as well as North and South America. 80% of large animals
became extinct around the same time as the first human presence in
America. Many people believe that humans, who may have entered
North America for the first time about 13,000 years ago, drove
woolly mammoths to extinction by overhunting. Increasingly more
scientists believe the timing of the arrival of the first humans
and the extinctions of most megafauna was not a coincidence. This
is known as the "Pleistocene overkill hypothesis," which takes
evidence from the rapid colonization and population growth of game-
hunting humans with large spears spreading throughout the
continent. Many weapons and mass hunting sites have been
discovered. There is clear archaeological evidence for human
hunting to be the only cause of the disappearance of mammoths and
mastodons, as well as other megafauna.
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5 COLONIZING NEW AREAS With the ever increasing population, the
human need for space and resources is increasing at an alarming
rate. These acquisitions are at the expense of biodiversity. When
new areas become inhabited by humans for urban, agriculture, or
other purposes, the amount of vegetation and number of animals
decreases, while the amount of heat, pollution, species competition
and other problematic effects to the environment increase. Land
development for humans use results in some of the biggest causes of
animals becoming endangered and extinct. This severely damages
biodiversity. Humans have also hunted animals all throughout
history, especially in new lands for food, sport or extermination
purposes. The first arrival of humans to any oceanic island with no
previous human inhabitants, has historically always triggered a
mass extinction of the island biota. Popular examples are the Moas
of New Zealand and Madagascars giant lemurs. There are many species
with weakened gene pools due to human domestication and breeding
techniques.
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EFFECTS OF LAND DEVELOPMENT Habitat fragmentation Habitat loss
and degradation Rainforest destruction Introduction of invasive
non-native species Climate change/ Pollution Global warming
Pollution- industrial waste, plastic trash, oil spills Disease
Hunting and fishing the new species found Changing landscapes
increases the instance of wildfires 6
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7 HABITAT FRAGMENTATION Habitat fragmentation is often a cause
of species becoming endangered. Fragmentation occurs when land
conversions, such as roads are made that break apart, or fragment,
the natural, preferred territory of species. Many species need
large, continuous areas of land to survive and reproduce
successfully. Population fragmentation can occur, dividing the
members of a species. Over time, this weakens their gene pool. Some
populations can be pushed to the edge of a habitat where the
climate can be different and the smaller, crowded population that
is left is less adaptable to these changes than the larger,
original population. Competition is high between species in the new
crowded habitat. Fragmentation of land greatly affects some
species, such as tigers, which have been endangered since
1969.
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HABITAT DEGRADATION Humans have greatly changed between 40 to
50 % of the Earths land surface for our own use and benefit.
Habitat loss and degradation affects 86% of all threatened birds,
86% of threatened mammals and 88% of threatened amphibians.
Habitats all over the world are constantly being altered for
reasons such as agriculture, lumber, urban development and
processing of many other resources. Human development of land often
involves the slash-and-burn method of land clearing, which can
greatly affect the native ecosystem. Many animals die in the fires.
8
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RAINFOREST DESTRUCTION In some parts of the world, 90% of the
forest has been destroyed in the past 150 years. Almost all of both
temperate-boreal and tropical rainforests have been reduced by at
least half of the original extent they covered before widespread
human destruction of rainforests. The tropical rainforests are the
most biologically diverse places on land. It is easy to see how so
many species are being lost. Many animals are endemic to the
tropical areas being destroyed, and those species are lost most
quickly. Animals indigenous to islands are at a greater risk of
being endangered. Many famous extinct animals, such as the dodo and
moa birds, were indigenous to isolated, tropical islands and had
never seen the likes of any large mammal. When the islands were
colonized by humans the birds quickly went extinct. 9
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INTRODUCTION OF INVASIVE SPECIES It is estimated that 40% of
all extinctions in the past 400 years are because of introduced
(non-native) species. Although most of these introductions were
accidents and only few deliberate, they all result in massive
changes in habitats and complications to the natural predator-prey
relationships. Invasive species often invade land that has already
been altered or created by humans. They are able to do so well and
outcompete the native species mostly because they have no natural
predators there. In some instances, introduced species spread
disease to the native populations. 10
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INVASIVE LAND ANIMALS The European rabbit was released to many
areas throughout the world to be used as food and for game hunting.
This rabbit is now a huge pest in New Zealand and Australia. They
overgraze vegetation, breed quickly and their very large
populations can transform the landscape and greatly alter the
ecological balance. The American grey squirrel was introduced to
Europe, where the red squirrel of Europe and Asia was prominent.
The grey squirrel has superior strength, is more aggressive and its
diet more easily adaptable than the red. Changes of the woodland
habitat also endangers the red in favor of the grey squirrel.
Another devastating factor is that many grey squirrels carry a pox
virus that is fatal to the red squirrels. 11
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12 INVASION IN AQUATIC ENVIRONMENTS It is estimated that 3,000
species of aquatic life, such as algae, bacteria, phytoplankton and
plants are carried around in the ballast water of ships all over
the world. Sometimes this can be extremely harmful to natural
environments. Of the 40 recorded extinctions of freshwater fish in
North America, 27 are attributed to the effects of introducing
non-native species. The Nile perch was introduced in Lake Victoria
in Africa as a game fish. It destroyed more than half of the 500
species of the chichlid fish. The variety of the chichlid had once
brought fame to Africas Rift Valley lakes, now over 300 species are
extinct.
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ZEBRA MUSSELS The zebra mussel is a freshwater mussel that was
brought from Europe to Canadian and North American streams and
rivers in ballast water of boats. Now, in the first river in North
America that was invaded by zebra mussels almost all 24 species of
pearly mussel found have gone extinct. This mussel has had a
profound effect on aquatic ecosystems: The finger nail-sized mussel
multiples to enormous numbers. They can live on any hard surface,
even shells of other mussels and they clog up large water pipes,
which cost $267 million between 1989 and 2004. The large numbers of
the zebra mussels consume so much phytoplankton that they starve
native mussels and zooplankton. 13
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14 INVASIVE PLANTS Caulerpa is an invasive, tropical seaweed.
It was dumped into the Mediterranean Sea when the Monaco public
aquarium cleared out their displays. In 15 years, the plant had
carpeted 10,000 acres of the sea floor around the coasts of France,
Spain and Italy. The carpet it forms is thick and densely packed,
with about 12,500 fronds per square yard, making it impossible for
fish to get through it to feed on organisms in the mud. The toxic
Caulerpa has replaced native grasses that feed molluscs, sea
urchins and some fish. In Tahiti, invasive miconia trees cover 2/3
of the island and cause soil erosion, resulting in landslides. They
threaten 40 to 50 species of indigenous plant life on the forest
floor, because they create impenetrable shade. Kudzu, also known as
the vine that ate the south, and mile-a-minute vine, currently
covers over seven million acres of land in the southern U.S. Kudzu
was introduced in 1876, and was advocated for use as animal feed,
for ornamental purposes and for soil erosion control until about
1953. In 1972, it was declared a weed. Although it can provide food
for many grazing animals, the thick vines block out sunlight,
destroying much of the native forests. Most herbicides have no
effect, and scientists who study how to get rid of the plant say
that it takes about 4 to 10 years of herbicide treatment to kill
Kudzu. Dr. James H. Miller of the U.S. Forest Service in Auburn,
Alabama has found an herbicide that makes Kudzu grow even better.
Many citizens of the southern U.S. have found interesting uses for
the vine, such as basket weaving, cooking and even making bales to
feed grazing farm animals.
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OTHER INVASIVE SPECIES The Argentine ant is now almost globally
distributed. They form super colonies of thousands of genetically
identical ants in giant nests that can span over a mile. The ants
attack native insect species all over the world, including other
ant species. They greatly alter the food webs of the native
species. In Spain native ants that disperse seeds are being
excluded. These ants also take pollinators away from native flowers
and greatly alter the communities of native ants and other
ground-dwelling insects. The giant cane toad was introduced to
Australia to eradicate a beetle that attacks sugar cane. Within six
days, the toads had laid eggs, in a pond specially constructed for
them. A year later, 41,000 baby toads were distributed to sugar
cane farmers. The pond was constantly filled with hundreds of
thousands of eggs by the toads. The toads could not eat the cane
beetle larvae that were hidden inside cane stems, so instead they
ate other insects. The cane toads are very poisonous and many
native predators have been pushed on to the endangered species list
as a result. Freshwater crocodile populations have crashed by 77%
from exposure to cane toads. 15
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A LITTLE ABOUT CLIMATE CHANGE Greenhouse gases: In 2002,
burning fossil fuels released 23 billion tons of carbon dioxide
into the atmosphere. The concentration of methane in the atmosphere
has doubled over the past few hundred years. It is estimated that
methane will cause 15 to 17 % of all global warming in America.
There is 20% more nitrous oxide in the atmosphere than there was at
the beginning of the industrial revolution. There is a distinct
correlation between increased CO 2 emissions caused by humans and
the increasing CO 2 in the atmosphere. Trees in forests help cool
the planet by absorbing around half a billion tons of CO 2
annually. Replacing forests with impervious surfaces, such as roads
and parking lots, increases the amount of heat and CO 2 in urban
areas, as well as the instance of wildfires in the altered
habitats. Scientists have even discovered that oceans absorption of
manmade CO 2 has decreased. These are just a few of the factors
leading to climate change, that many scientists believe is leading
to a massive warming of the planet. During global warming, climate
change occurs by climate patterns leaping from one stable state to
the next. These drastic climate changes were referred to by
climatologist Julia Cole as magic gates, two of which have occurred
(in 1976 and 1998) since temperatures began slowly rising in the
1970s. For example, In 1976, Alaska had unprecedented mild
conditions, while the 48 lower American states had blizzards.
Climate changes have already seriously affected some species and
many scientists fear for the well-being of numerous species that
could be affected by this global phenomenon. Marine species, which
are extremely sensitive to temperature fluctuations, are at high
risk to be endangered by global warming. 16
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A LITTLE ABOUT POLLUTION Pollution in freshwater and marine
habitats has been devastating to the species that live there. From
dumped industrial and other chemical waste, runoff from agriculture
and other chemicals to just plain piles of trash in our oceans, it
is all pollution. It is estimated that 44% of marine pollution
comes from land and floats down rivers to estuaries, where it
bleeds into the sea. 33% is airborne pollution that is deposited
far off shore. The complications from pollution puts numerous
species at risk of becoming extinct. The excessive nutrients in
waste water and agricultural runoff has caused eutrophication and
increased the frequency and severity of red tides. Oil spills are a
highly publicized form of ocean pollution. Many animals die and
many are threatened with extinction because of this. Penguins and
other water birds, seals, sea lions, etc. are seriously affected by
oil spills. 17
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SHEER NUMBERS It may be surprising and hard to believe to hear
how many species are thought to go extinct every year, but we have
to keep in mind that there are far more species that we dont even
know exist. Most scholars would agree that there are between 5 and
15 million species on Earth, not including bacteria, etc. Recorded
extinctions involve mostly large, visible birds and mammals.
Invertebrates have been much less well studies than mammals, etc.
However there are more of those smaller organisms in existence.
Many scientists do not believe that the endangered arthropod
estimates accurately reflect what is happening, because there is
still so much left undiscovered. There are 15 to 20 thousand
species of butterflies in the world. It is the generally accepted
estimate that 4.9 to 6.6 million species of insects exist. However,
some estimates suggest that there may be 5-10 million species of
insects that have yet to be discovered by science. A more
astounding figure from a study conducted by Terry Erwin of the
Smithsonian Institution has been highly criticized. He estimates
that there are 30 million species of arthropods in tropical forests
alone. More and more other scientists are starting to believe this
is not that unreasonable of an estimate. In the Peruvian Amazon, 43
species of ants can be found on a single tree! Thats the entire ant
fauna in the whole United Kingdom! There were 24,000 species of
named fish in the early 1990s, with 100 bony fish alone being added
each year. Currently about 10,000 species of birds exist and based
on the fossil record, it is estimated that 150,000 to 1,634,000
species of birds have ever existed. 18
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ENDANGERED/THREATENED SPECIES According to the IUCN there are
over 5,000 severely endangered species. This includes species from:
Mammals Marsupials Fish Birds Reptiles Amphibians Arthropods
19
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20 ENDANGERED LAND ANIMALS There are several types of Primates
that are endangered. Numerous species of monkeys, gibbons and great
apes are at great risk of becoming extinct. The group of
600-something mountain gorillas remaining in the wild have low
genetic diversity. Anteaters, sloths and armadillos all have
specific diets, making them all the more affected by habitat loss,
which is their biggest threat. Many species are affected in areas
from South and Central America through Latin America to the
southern United States. Deforestation for livestock, crops, lumber
extraction and even charcoal production has lessened the habitats
of all anteaters, sloths and the giant armadillo. In addition, they
are slow moving and easily fall victim to the slash-and-burn land
clearing fires. Many of these insect-eating animals are hunted for
extermination. The giant anteater and armadillos are valued, mostly
for their meat, but also for various body parts such as fur, claws
and shell. Overhunting and damage to their specialized habitats has
seriously endangered one out of every four species of rabbit. In
South Africa, the bushman hare has lost over 2/3 of its habitat in
the past 50 years. In the Great Basin area of the United States,
the pygmy rabbit, which is the smallest rabbit, relies on only a
few species of sagebrush for over 90% of its food and for shelter.
It is extremely vulnerable to habitat degradation. Rhino species
are seriously endangered from overhunting and loss of their
habitat. There are many other endangered land dwelling animals such
as marsupials, pigs, hippos, giraffes, elephants, camels, deer,
cattle, horses and squirrels, as well as many types of dogs and
many types of cats big and small.
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21 ENDANGERED MARINE SPECIES The numbers of the 12 species of
Baleen whales have been greatly diminished because of large-scale
hunting, called whaling, which has been mostly illegal since 1986.
Also known as great whales, these giant water mammals are
negatively affected by pollution, such as oil spills, floating
plastic debris and dumped industrial waste. Stocks of the whales
prey are being sucked up by mechanic fishing fleets. They can also
get tangled in fishing nets and drown and some have harmful
collisions with boats. Oceans are becoming more noisy, which may
interfere with their already-slow mating process. Estimates for the
blue whale range from 4 to 15 thousand, while there are less than
300 of the North Atlantic right whale. Sharks have been around for
430 million years and there are about 330 species! Humans have
utilized parts of sharks for centuries, from their skin and meat to
their oil and their teeth and bones. The worst threat to sharks is
being overfished for their meat, flesh and fins. The demand for
their fins to make shark fin soup is currently the biggest cause of
declining populations. Up to 100 million sharks are caught just to
make this soup. Rays, which are closely related to sharks, live in
small populations in narrow habitat ranges along the sea bottom.
They are not strong swimmers and they are very susceptible to
environmental changes, due to their small population numbers. There
are 450 species and almost all of them are under threat from
overexploitation. Some are hunted for their pectoral fins, which
have a distinct flavor and texture. They are harpooned and caught
in gill nets for food in Mexico and the Philippines. These rays are
severely affected by bottom trawling, which can destroy entire
habitats in minutes.
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TOOTHED WHALES Toothed whales are all highly social and
carnivorous, feeding on squid, shellfish, fish, etc. There are 70
species including dolphins, porpoises and several different groups
of whales that suffer many of the same threats as the great whales.
These whales and dolphins are far more vocal than baleen whales,
and their behavior can be greatly affected from vibrations in the
water from mining explosions, boat engines, etc. Some even die due
to internal injuries from this underwater sound energy. Thousands
of the smaller species die each year from drowning in fishing nets.
They suffer from a greater instance of serious disease because
pollutants in the water can weaken immune systems. They can also
mistake pieces of floating trash for fish and swallow them, which
eventually results in starvation. There are less than 250 of the
vaquita porpoise in the wild, and more than 20 are killed in shrimp
and shark nets every year. There are five species of river
dolphins, freshwater members of the toothed whales, and they are
all seriously threatened. One river dolphin is critically
endangered, with less than 100 of them left. These river dolphins
are hunted as food. Their food supplies have been greatly reduced
by chemical pollutants, extraction of river water and dams, which
block the seasonal movement of the dolphins and their prey. 22
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DUGONGS AND MANATEES Manatees and dugongs, also called sea
cows, are vegetarians. They eat aquatic plants in shallow areas of
water. The one species of dugong has short front flippers and its
tail is shaped like a whales. Manatees have longer fore flippers
and a rounded tail. At one time, the Stellers sea cow, the largest
of all dugongs and manatees, inhabited the Pacific Rim from Japan
to California. Climate change and native hunting had reduced their
range to around Alaska where there were thought to be one to two
thousand individuals. A Russian explorer, Captain Vitus Bering,
first saw and described the Steller's sea cow in 1741 when he and
his crew had become stranded on their ship in Alaska for the
winter. Berings crew killed many of the remaining dugongs for their
meat and hides. Later expeditions to the area killed the rest of
the Stellers sea cow and it was extinct by about 1768. Manatees
& dugongs now consist of only four species. The world
population for all four species is estimated to be fewer than
150,000 and they are predicted by some scientists to be extinct by
2030. 23
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24 ENDANGERED FRESHWATER SPECIES Molluscs, both fresh and salt
water, are overfished for their shells and flesh, threatened by
water pollution, habitat destruction and outcompeted by invasive
species. Many freshwater fish are endemic to specific river areas
and sudden changes in their environment endangers them. Diverting
rivers, damming and extracting water all put fish at risk. The flow
of nutrients and water is stopped and fish cannot get to their
spawning grounds. By the 1950s, the thicktail chub fish of
California had died out due to the effects of a series of dams.
Silt is a major problem in water bodies, as it lowers the quality
of water and suffocates aquatic life. Another United States fish,
harelip sucker, went extinct due to river siltation. Many species
are threatened by the introduction of non-native fish. Pollution is
another widespread problem for freshwater fish. Acid rain has
caused a 100% mortality rate in some Canadian lakes. All kinds of
industrial waste and chemical runoff pollute rivers and kill
freshwater fish. The biodiversity of the Great Lakes has been
severely diminished due to pollution. Endemic pearly mussels are
the most threatened freshwater animal in North America. Of the 300
species that have been described, 12% are thought to be extinct and
another 60% are endangered and threatened. Populations of pearly
mussels have been over-harvested and their river habitats polluted
by humans. In New Yorks Hudson River, native pearly mussels were
reduced to a tenth of their densities by these actions. They are
also in danger from the invasive zebra mussel.
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25 ENDANGERED BIRDS Songbirds suffer from a severely depleted
food source, increased predation rates and poor breeding seasons
because of habitat loss, especially things like deforestation and
the drainage of wetlands. Seventy-two species were critically
endangered in 2006. The seven-colored tanager lives only in the
remaining 2% of Brazils Atlantic forest. Hummingbirds worst threat
is habitat loss. This is primarily due to the destruction of
nesting sites. Owls thought to be extinct, are sometimes found, as
are new species. This proves how much we still do not know, but
doesnt mean the threat is any less serious. The single greatest
danger to owls is habitat loss, although they fall victim to a
number of other threats, such as the use of pesticides, like DDT.
The most endangered owls are endemic to their habitats. Less than
2,000 of the Puerto Rican nightjar are still alive. The decline of
the northern spotted owl of North America has been highly
publicized. The last three of the Spixs Macaw Parrot species were
captured in 1987 and 1988, making them extinct in the wild. Parrots
are the most endangered birds in the world. Over 1/3 of all parrot
species are endangered. The caged bird trade and rapid
deforestation are destroying parrot populations. Many members of
the family of doves, or pigeons, are endangered and many have
already become extinct from overexploitation. They are also very
affected by deforestation. For example, the pink pigeon of
Mauritius was a victim of habitat loss. The clearing of the
evergreen tree and brush habitat caused the population to fall
below 20 in the 1980s and they are now being bred in captivity.
Extinct doves include the dodo bird and the passenger pigeon. One
in six species of pelicans and herons are endangered due to
overhunting, toxic agrochemicals and industrial pollution, drainage
of marshes for both land conversion and water extraction,
diminishing food populations, and the poor breeding seasons brought
on by all of these changes. Numerous other birds are endangered,
including waterfowl, gulls, eagles, hawks, falcons, cranes &
relatives, hornbills, woodpeckers, albatrosses, and vultures.
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ENDANGERED FLIGHTLESS BIRDS There are 17 species of penguins.
Overexploitation for their meat and to produce oil caused huge
losses to penguin populations in the past. Recent shifts in climate
and habitat, such as ocean currents and water temperature, change
the migratory path of many penguins prey away from their breeding
sites. The increase in floating ice in the Antarctic is feared to
seriously reduce the breeding success of the four species that live
there. Non-native animals are a serious threat to penguins. The
yellow-eyed penguin, found only on New Zealands South Island,
neared extinction due to attacks by introduced cats, rats, dogs and
ferrets as well as disturbance of nests by humans and sheep. They
now have hope for the future, as they are intensely protected.
Other flightless birds in danger of extinction include ostriches
and their relatives as well as many game birds. 26
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ENDANGERED REPTILES Numerous species of reptiles are endangered
from many causes, but primarily habitat disruption, hunting and
pollution. Endangered reptiles include snakes, lizards, turtles,
crocodiles and alligators. Crocodiles and alligators have been
hunted a long time by humans for their meat and skin, however the
most serious problem endangering them is the destruction of their
swamp and river habitats. There are two species of alligator and
the population of the critically endangered Chinese alligator in
the wild is about 1,000 individuals. In Asia, 15 of the 19 species
of freshwater turtle are critically endangered. All over the world,
different species of freshwater turtle are targeted for their meat
and sometimes their eggs. One species of turtle has been eaten to
death by humans. Overcollection of turtles can cause extinction of
small populations. Although the development of waterfront
properties and destruction of nesting grounds has taken a toll on
some turtles, the biggest danger they face is overexploitation. All
eight species of sea turtle are endangered. In 2002, there were
20,000 to 30,000 adult, female leatherback sea turtles in the
world. There had been about 115,000 in 1982. Now, with as few as
2,300 adult females, these turtles are experiencing serious
population declines. The most serious problems for the leatherback
include hunting and egg collection, pollution, loss of nesting
habitat from beach development and beach erosion, which has been
linked to global climate change. 27
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ENDANGERED ARTHROPODS Some scientists estimate that 10% of the
worlds insects are threatened. The Queen Alexandra birdwing
butterflies are the largest butterfly in the world. Some have a
wingspan reaching nearly 10 inches, which is larger than many
birds! It is threatened by the clearing of forest for town building
and farming, as well as the expanding commercial rubber and cocoa
plantations. These butterflies had a very localized distribution in
the forests of northern Papua New Guinea, but now they are very
rare throughout that range. Many other kinds of butterflies all
over the world have been endangered an some have gone extinct. The
biggest cause is habitat degradation and destruction by humans,
such as building roads and clearing the forest for lumber and
agriculture. Butterflies are dependent on natural habitat, making
them extremely sensitive to human disturbances. Extinct butterflies
include the Xerces Blue butterfly from the United States and the
Large Copper butterfly from the British Isles. 28
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EXTINCTIONS Innumerable species have been lost in human
history. This includes members of all groups of life: Bird species
Land animal species Amphibian and reptile species Aquatic animals
Aquatic and terrestrial plant species 29
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BIRD EXTINCTIONS Moas were a group of large, flightless birds,
containing 24 species. The largest could get up to 10 feet tall!
Moas lived on the isolated islands of New Zealand. Around 700 A.D.,
Polynesians colonized New Zealand and began hunting the preferred
food source, the largest animal on the islands: the Moa. Dogs and
rats that came to the islands with the Polynesians ate young Moa
chicks. These Polynesians were the Maori, who used burning to alter
the ecosystem in favor of certain plants and fish that they
preferred. This extensive burning caused severe habitat alteration.
All of the species were extinct by the time the islands were
settled by Europeans in the 1600s. More than 60 extinct species of
stork and heron are only known from fossils. 30
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31 PASSENGER PIGEON In the 1800's, the passenger pigeon
population had more individuals than all other North American birds
combined. A single flock of passenger pigeons could have over 2
billion birds and there were multiple flocks of birds in the United
States. The flocks were basically described as an endless sea of
birds blackening the sky, etc. The nesting colonies of the
passenger pigeon in northeastern deciduous forests could be 20
miles across, with so many birds per tree that the branches broke
from their weight. The passenger pigeons' migration and nesting
behavior made them easy to hunt in large numbers. They were netted,
shot and smoked out of trees with sulfur torches. Special firearms,
including an early version of the machine gun, were used to harvest
these birds in enormous quantities. By 1850, several thousands of
people were employed in the passenger pigeon industry. One
operation in New York processed 18,000 pigeons each day in 1855 and
in Michigan, a billion birds were harvested in one year alone! The
passenger pigeon population collapsed due to uncontrolled
commercial hunting for their meat. Although several thousand birds
still survived in 1880, the population continued to decline and was
extinct in the wild by 1900, reduced to just one individual, named
Martha, who died in captivity at the Cincinnati Zoo in 1914. The
breeding patterns of the passenger pigeons may have required a
community of numerous individuals to stimulate the necessary cycles
or behaviors, which would help explain the pigeon's inability to
recover from overhunting. The scattered populations after 1880
would not have been concentrated enough in any one area to
stimulate these breeding behaviors. Without their massive
populations, it may have also been more difficult for the passenger
pigeons to find suitable mates and to compete with other birds for
the increasingly fewer nest sites in the disappearing deciduous
forests.
Slide 32
CARIBBEAN MONK SEAL The Caribbean monk seal was scientifically
recorded by Columbus in 1493 during his famous voyage to the
Americas. This marine mammal had lived in the tropical waters of
the West Indies for thousands of years and was well known by the
native people. During the 1600s, their numbers declined because
they were extensively hunted by exploring Spaniards. They were
mostly killed by fishers who saw them as unwanted competitors. This
seal was already rare by the 1700s. In 1922, the last recorded
Caribbean Monk Seal in the U. S. was killed off the coast of Key
West, Florida. Currently several related species of seals around
the world are endangered. The Hawaiian monk seal and the
Mediterranean monk seal are similar to the Caribbean monk seal, and
are also despised by fishers. 32
Slide 33
33 ARTHROPOD EXTINCTIONS According to the IUCN in 2007, 59
insect species are known to have gone extinct in our modern time,
however, thousands are estimated to have disappeared. In the United
States alone, 160 insect species are thought to be extinct. Since
only a very small percentage of insect diversity has actually been
assessed, the number of species that went extinct within the last
100 years is likely to be very high. From butterflies to
crustaceans, many arthropods have become extinct in human history.
Non-insect arthropods are endangered in many ways, but extinction
is mainly caused by overexploitation. The largest factors in insect
extinction are: Invasive species Habitat loss Pesticide use
Slide 34
34 SOURCES Birmingham, Eldredge et. al. 2005. Tropical
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Flannery, Tim. 2005. The Weather Makers How Man is Changing the
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