The sixth mass extinction Human Accountability for Species Becoming Endangered and Extinct. Erica Hardin 4-26-2012 Environmental Biology. Introduction. Since modern humans have existed, the rate of species extinction has abruptly increased.
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.