Presentation Transcript

1. The sixth mass extinctionHuman Accountability for Species Becoming Endangered and Extinct

   Erica Hardin 4-26-2012 Environmental Biology
2. 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.
3. 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 km2. 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/km2 or less. Human population is up to 400 times greater than natural carrying capacity.
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, Homosapiens. 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.
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 human’s 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 Madagascar’s giant lemurs. There are many species with weakened gene pools due to human domestication and breeding techniques.
6. 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
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.
8. Habitat degradation Humans have greatly changed between 40 to 50 % of the Earth’s 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.
9. 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.
10. 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.
11. 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.
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 Africa’s Rift Valley lakes, now over 300 species are extinct.
13. 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.
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.
15. 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.
16. 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 CO2 emissions caused by humans and the increasing CO2 in the atmosphere. Trees in forests help cool the planet by absorbing around half a billion tons of CO2 annually. Replacing forests with impervious surfaces, such as roads and parking lots, increases the amount of heat and CO2 in urban areas, as well as the instance of wildfires in the altered habitats. Scientists have even discovered that oceans’ absorption of manmade CO2 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.
17. 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.
18. Sheer numbersIt 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 don’t 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! That’s the entire ant fauna in the whole United Kingdom! There were 24,000 species of named fish in the early 1990’s, 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.
19. 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
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.
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.
22. 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.
23. 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 whale’s. Manatees have longer fore flippers and a rounded tail. At one time, the Steller’s 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 Alaskawhere there were thought to be one to two thousand individuals. ARussian 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. Bering’s crew killed many of the remaining dugongs for their meat and hides. Later expeditions to the area killed the rest of the Steller’s 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.
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 York’s 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.
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 Brazil’s 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 doesn’t 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 Spix’s 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.
26. 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 Zealand’s 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.
27. 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. Overcollectionof 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.
28. Endangered arthropods Some scientists estimate that 10% of the world’s 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.
29. 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
30. 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.
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 enoughin 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.
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.
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
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