Invasive Species (9.8) Endangered Species (9.9)
Invasive Species
Exotic species, also known as alien species, are species that live outside their historical range. For example, honeybees were introduced to North America in the 1600s to provide a source of honey for European colonists. Red foxes, now abundant in Australia, were introduced there in 1800s for the purpose of fox hunts, which were popular in Europe at the time.
During the past several centuries, humans have frequently moved animals, plants, and pathogens around the world. Some species are also moved accidentally. For example, rats that stowed away in shipping containers ended up on distant oceanic islands. Because these islands never had rats or other ground predators, there had never been any natural selection against nesting on the ground, and numerous island bird species had evolved to nest on the ground.
When the rats arrived in places such as Hawaii, they found the eggs and hatchlings from ground nests an easy source of food, resulting in a high rate of extinction in ground-nesting birds. Similar accidental movements have occurred for many pathogens, including exotic fungi that were introduced to North America nearly a century ago and have since killed nearly all American elm and American chestnut trees in eastern North America. Similarly, an exotic protist that causes avian malaria has driven many species of Hawaiian birds to extinction. Other movements of exotic species are intentional, such as exotic plants that are sold in greenhouses for houseplants and outdoor landscape plants, or exotic animals that are sold as pets or to game ranches that raise exotic species of large mammals for hunting.
In most cases, exotic species fail to establish successful populations when they are introduced to a new region. For the small percentage of introductions that are successful, exotic species can live in their new surroundings and have no negative effect on the native species. In other cases, however, the exotic species rapidly increase in population size and cause harmful effects on native species. When exotic species spread rapidly across large areas and cause harm, we call them invasive species. Rapid spread of invasive species is possible because invasive species, which have natural enemies in their native regions that act to control their population, often have no natural enemies in the regions where they are introduced. Two of the best-known examples of invasive exotic species in North America are the kudzu vine and the zebra mussel.
The kudzu vine is native to Japan and southeast China but was introduced to the United States in 1876. Throughout the early 1900s, farmers in the southeastern states were encouraged to plant kudzu to help reduce erosion in their fields. By the 1950s, it became apparent that the southeastern climate was ideal for kudzu, with growth rates of the vine approaching 0.3m per day. Because herbivores in the region do not eat kudzu, the species has no enemies and can spread rapidly. The vine grows up over most wildflowers and trees and shades them from the sunlight, causing the plants to die. Indeed, the vine grows over just about anything that does not move. Kudzu currently covers approximately 3 million hectares (7.4 million acres) in the United States.
- Invasive species are species that can live, and sometimes thrive, outside of their normal habitat. Invasive species can sometimes be beneficial, but they are considered invasive when they threaten native species
- Invasive species are often generalist, r-selected species and therefore may outcompete native species for resources
- Invasive species can be controlled through a variety of human interventions
Exotic species, also known as alien species, are species that live outside their historical range. For example, honeybees were introduced to North America in the 1600s to provide a source of honey for European colonists. Red foxes, now abundant in Australia, were introduced there in 1800s for the purpose of fox hunts, which were popular in Europe at the time.
During the past several centuries, humans have frequently moved animals, plants, and pathogens around the world. Some species are also moved accidentally. For example, rats that stowed away in shipping containers ended up on distant oceanic islands. Because these islands never had rats or other ground predators, there had never been any natural selection against nesting on the ground, and numerous island bird species had evolved to nest on the ground.
When the rats arrived in places such as Hawaii, they found the eggs and hatchlings from ground nests an easy source of food, resulting in a high rate of extinction in ground-nesting birds. Similar accidental movements have occurred for many pathogens, including exotic fungi that were introduced to North America nearly a century ago and have since killed nearly all American elm and American chestnut trees in eastern North America. Similarly, an exotic protist that causes avian malaria has driven many species of Hawaiian birds to extinction. Other movements of exotic species are intentional, such as exotic plants that are sold in greenhouses for houseplants and outdoor landscape plants, or exotic animals that are sold as pets or to game ranches that raise exotic species of large mammals for hunting.
In most cases, exotic species fail to establish successful populations when they are introduced to a new region. For the small percentage of introductions that are successful, exotic species can live in their new surroundings and have no negative effect on the native species. In other cases, however, the exotic species rapidly increase in population size and cause harmful effects on native species. When exotic species spread rapidly across large areas and cause harm, we call them invasive species. Rapid spread of invasive species is possible because invasive species, which have natural enemies in their native regions that act to control their population, often have no natural enemies in the regions where they are introduced. Two of the best-known examples of invasive exotic species in North America are the kudzu vine and the zebra mussel.
The kudzu vine is native to Japan and southeast China but was introduced to the United States in 1876. Throughout the early 1900s, farmers in the southeastern states were encouraged to plant kudzu to help reduce erosion in their fields. By the 1950s, it became apparent that the southeastern climate was ideal for kudzu, with growth rates of the vine approaching 0.3m per day. Because herbivores in the region do not eat kudzu, the species has no enemies and can spread rapidly. The vine grows up over most wildflowers and trees and shades them from the sunlight, causing the plants to die. Indeed, the vine grows over just about anything that does not move. Kudzu currently covers approximately 3 million hectares (7.4 million acres) in the United States.
The zebra mussel is native to the Black Sea and the Caspian Sea in eastern Europe and western Asia. Over the years, large cargo ships that traveled in these seas unloaded their cargo in the ports of the Black Sea and Caspian Sea and then pumped seawater into the holding tanks to ensure that the ship sat low enough in the water to remain stable. This water that is pumped into the ship is called ballast water. When the ships arrived in the St. Lawrence River and the Great Lakes, they loaded on new cargo and no longer needed the weight of the ballast water, which they pumped out of the ship into local waters. One consequence of transporting ballast water from Asia to North America is that many aquatic species from Asia, including zebra mussels, have been introduced into the aquatic ecosystems of North America. Because the St. Lawrence River and the Great Lakes provided an ideal ecosystem for the zebra mussel, and because in a single zebra mussel can produce up to 30,000 eggs, the mussel spread rapidly through the Great Lakes ecosystem. On the positive side, because the mussels feed by filtering the water, they remove large amounts of algae and some contaminants, which helps to counteract the cultural eutrophication that has occurred in the Great Lakes Ecosystem. On the negative side, the zebra mussels physically crowd out many native mussel species and the zebra mussels can consume so much algae that they negatively affect native species that also need to consume the algae. Moreover, the invasive mussels can achieve such high densities that they can clog intake pipes and impede the flow of water on which industries and communities rely.
A new threat to the Great Lakes is the silver carp, a fish that is native to Asia but has been transported around the world in an effort to consume excess algae that accumulates in aquaculture operations and the holding ponds of sewage treatment plants. After being brought to the United States, some of the fish escaped and rapidly spread through many of the major river systems, including the Mississippi River. Over the years, the carp population has expanded northward, and by 2010 it approached a canal where the Mississippi River connects to Lake Michigan. Although researchers detected the DNA of the carp in water samples from the Great Lakes from 2009 to 2011, substantial netting efforts in the spring of 2013 failed to find any of the fish in the Great Lakes. As of 2018, it appeared that the carp had not yet found its way into the Great Lakes. There are two major concerns about this invading fish. First, scientists worry that it will out-compete native species of fish that also consume algae. Second, the silver carp has an unusual behavior; it jumps out of the water when startled by passing boats. Given that the carp can grow to 40 lb and jump up to 3 meters into the air, this poses a major safety issue to boaters.
Around the world, invasive exotic species pose a serious threat to biodiversity by acting as predators, pathogens, or superior competitors to native species. Some of the most complete data exist in Europe. During the past 100 years, Europe has experienced a steady increase of nearly 2,000 exotic species in terrestrial ecosystems. Additionally species have been introduced into freshwater and marine ecosystems. A number of efforts are currently being used to reduce the introduction of invasive exotic species, including the inspection of goods coming into a country and the prohibition of wooden packing crates made of untreated wood that could contain insect pests.
Endangered Species
Overharvesting causes declines in populations and species
Hunting, Fishing, and other forms of harvesting are the most direct human influences on wild populations of plants and animals. Most species can be harvested to some degree, but a species is over harvested when individuals are removed at a rate faster than the population can replace them. In the extreme, overharvesting of a species can cause extinction. In the 17th century, for example, ships sailing from Europe stopped for food and water at Mauritius, an uninhabited island in the Indian Ocean. On Mauritius, the sailors would hunt the dodo, a large flightless bird that had no innate fear of humans because it had never seen humans during its evolutionary history. The dodo, unable to protect itself from human hunters and the rats that consume dodo eggs and hatchlings, became extinct in just 80 years. The same scenario appears to have taken place with many other large animal species as well. These animals include the giant ground sloths, mammoth, American camels of North and South America, and the 3.7 meter tall Moa bird of New Zealand. Each species became extinct soon after humans arrived, suggesting that the animals’ demise may have been due to overharvesting.
Overharvesting has also occurred in the more recent past. In the 1800s and early 1900s, for example, market hunters slaughtered wild animals to sell their parts on such a scale that many species, including the American bison, declined dramatically. Bison were once abundant on the western plains, with estimates ranging from 60 to 75 million individuals. By the late 1800s fewer than 1,000 were left. This means that 99.999% of all bison were killed. Following enactment of legal protections, the Bison population today has increased and more than 500,000, including both wild bison and bison raised commercially for meat.
Not all species harvested by market hunters fared as well as the American bison. THe passenger pigeon was once one of the most abundant species of birds in North America. Population estimates ranged from three to five billion birds in the 19th century. In fact, during migrations, people observed continuous flocks of pigeons flying overhead for 3 days straight in densities that blocked out most of the sun. Breeding flocks could cover 40000 hectares (100,000 acres) with 100 nests built into each tree. With such high densities, market hunters could shoot or net the birds in very large numbers and fill train cars with harvested pigeons to be sold in eastern cities. This overharvesting, combined with the effects of forest clearing for agriculture, caused the passenger pigeon to decline quickly. The last passenger pigeon died in 1914 at the Cincinnati Zoo.
During the past century, regulations have been passed to prevent the overharvesting of plants and animals. In the United States for example, state and federal regulations restrict hunting and fishing of game animals particular times of the year and limit the number of animals that can be harvested. Similar agreements have been reached among countries through international treaties. In general, these regulations have proven very successful in preventing species declines caused by overharvesting. In some regions of the world, however, harvest regulations are not enforced and illegal poaching, especially of large, rare animals that include tigers, rhinoceroses, and apes, continues to threaten species with extinction. Harvesting rare plants, birds, and coral reef dwellers for private collections has also jeopardized the species.
Plant and Animal Trade
For some species, the legal and illegal trade in plants and animals represents a serious threat to their ability to persist in nature. One of the earliest laws in the United States to control the trade of wildlife was the Lacey Act. First passed in 1900, the act originally prohibited the transport of illegally harvested game animals, primarily birds and mammals, across state lines. Over the years, a number of amendments have been added so that the Lacey act today forbids the interstate shipping of all illegally harvested plants and animals.
At the international level, the United Nations convention on international trade in endangered species of wild fauna and Flora, also known as CITES was developed in 1973 to control the international trade of threatened plants and animals. Today, CITES is an international agreement among 182 countries throughout the world. The IUCN maintains a list of threatened species known as the Red List. Each member country assigned a specific agency to ensure and regulate the import and export of animals on the list. For example, in the United States, the U.S. Fish and Wildlife Service conducts this oversight.
Despite such International agreements, much illegal plant and animal trade still occurs throughout the world. In 2012, a report by the Congressional research service estimated that illegal trade in wildlife was worth 5 billion to 220 billion dollars annually. In 2017, it was estimated that 50,000 illegal shipments of wildlife and wildlife parts have been sent to United States ports over a 10-year period. In some cases, animals are sold for fur or for body parts that are thought to have medicinal value. For example, 1 kg of rhino horn can sell for $50,000. Other cases, rare animals are in demand as pets. For example, in 2001 a population of the Philippine forest turtle once thought to be extinct, was discovered on a single island in the Philippines. This animal, one of the most endangered species in the world, can not be traded legally, but demand for it as a pet has caused it to be sold illegally and the last remaining population has declined sharply in only a few years. A single turtle sells for $50 to $75 in the Philippines and up to $2,500 in the United States and Europe. Today, the turtle is critically endangered. Similar cases of illegal trade occur in rare species of trees for lumber such as big leaf mahogany, rare species of plants for medicinal use, and many rare species of orchids for their beautiful flowers.
Sometimes even when trade in a particular species is legal, it can pose a potential long-term threat to species persistence. In the southwestern United States, for example, there is a growing movement to reduce water used by replacing grass lawns with desert landscapes. One of the unintended consequences is increased demand for cacti and other desert plants that are collected from the wild. Sales are currently estimated to be $1 million annually. Given the slow growth of desert plants, this increased demand is causing height and concern for these plant populations in the wild.
The Endangered Species Act is designed to protect species from extinction. This act authorizes the US Fish and Wildlife Service to determine which species can be listed as threatened species or endangered species and prohibits the harming of such species, including prohibitions on the trade of listed species, their fur, or their body parts. IUCN threatened species have a high risk of extinction in the future and near threatened species are very likely to become threatened in the future. In the United States, an endangered species is defined as a species that is in danger of extinction within the foreseeable future throughout all or a significant portion of its range, whereas a threatened species is defined as any species that is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. The U.S. definition of endangered is similar to the international definition for threatened and the U. S.definition for threatened is similar to the international definition of near threatened.
The Endangered Species Act was first passed in 1973 and has been amended several times since then from the international perspective. The act also implements the international CITES agreement. To assist in the conservation of threatened and endangered species, the act authorizes the government to purchase habitat that is critical to the conservation of the species and to develop recovery plans to increase the population of threatened and endangered species. This is often one of the most important steps in allowing endangered species to persist. For example, grizzly bears in the greater Yellowstone ecosystem had 236 individuals in 1975. After being listed as endangered, steps were taken to protect the bear's favored habitat and today it numbers nearly 700 individuals.
As of 2018, the species that have been listed as threatened or endangered in the United States include 272 invertebrate animals, 442 vertebrate animals, and 947 plants. Although the listing process can take several years, once listed, many threatened and endangered species have experienced stable or increasing populations. In fact, some species have experienced sufficient increases in numbers to be removed from the endangered species list; these include the bald eagle, peregrine falcon, American alligator, and the Eastern Pacific population of the gray whale. Other species are currently increasing in number and maybe taken off the list in the future. The gray wolf, for example, was reintroduced into Yellowstone National Park to help improve the species abundance in the United States and it is now no longer endangered.
The Endangered Species Act has sparked a great deal of controversy in recent years because it can restrict certain human activities in areas where listed species live, including how landowners use their land. For example, some construction projects have been prevented or altered to accommodate threatened or endangered species. Organizations whose activities are restricted by The Endangered Species Act often try to pit the protection of listed species against the jobs of people in the region. In the 1990s, for example, logging companies wanted to continue logging the old growth forest of the Pacific Northwest. These forests are home to the threatened northern spotted owl and many other species that depend on old growth forest. Automation had caused a large decline in the number of logging jobs over the preceding several decades, and many loggers perceived the Endangered Species Act as a further threat to their livelihood. They denounce the act because they said it placed more value on the spotted owl than it did on the humans who depended on logging. In the end, a compromise allowed continued logging on some of the old growth forest while the rest became protected habitat.
During the past decade, several politicians and their constituents have attempted to weaken The Endangered Species Act. However, strong support from the public and scientists has allowed it to retain much of its original power to protect threatened and endangered species. The biggest current challenge is the lack of sufficient funds and personnel required to implement the law.
- A variety of factors can lead to a species becoming threatened with extinction, such as being extensively hunted, having limited diet, being outcompeted by invasive species, or having specific and limited habitat requirements
- Not all species will be in danger of extinction when exposed to the same changes in their ecosystems. Species that are able to adapt to change in their environment or that are able to move to a new environment are less likely to face extinction.
- Selective pressures are any factors that change behaviors and fitness of organisms within an environment
- Species in a given ecosystem compete for resources like territory, food, mates, and habitat, and this competition may lead to endangerment or extinction
- Strategies to protect animal populations include criminalizing poaching, protecting animal habitats, and legislation.
Overharvesting causes declines in populations and species
Hunting, Fishing, and other forms of harvesting are the most direct human influences on wild populations of plants and animals. Most species can be harvested to some degree, but a species is over harvested when individuals are removed at a rate faster than the population can replace them. In the extreme, overharvesting of a species can cause extinction. In the 17th century, for example, ships sailing from Europe stopped for food and water at Mauritius, an uninhabited island in the Indian Ocean. On Mauritius, the sailors would hunt the dodo, a large flightless bird that had no innate fear of humans because it had never seen humans during its evolutionary history. The dodo, unable to protect itself from human hunters and the rats that consume dodo eggs and hatchlings, became extinct in just 80 years. The same scenario appears to have taken place with many other large animal species as well. These animals include the giant ground sloths, mammoth, American camels of North and South America, and the 3.7 meter tall Moa bird of New Zealand. Each species became extinct soon after humans arrived, suggesting that the animals’ demise may have been due to overharvesting.
Overharvesting has also occurred in the more recent past. In the 1800s and early 1900s, for example, market hunters slaughtered wild animals to sell their parts on such a scale that many species, including the American bison, declined dramatically. Bison were once abundant on the western plains, with estimates ranging from 60 to 75 million individuals. By the late 1800s fewer than 1,000 were left. This means that 99.999% of all bison were killed. Following enactment of legal protections, the Bison population today has increased and more than 500,000, including both wild bison and bison raised commercially for meat.
Not all species harvested by market hunters fared as well as the American bison. THe passenger pigeon was once one of the most abundant species of birds in North America. Population estimates ranged from three to five billion birds in the 19th century. In fact, during migrations, people observed continuous flocks of pigeons flying overhead for 3 days straight in densities that blocked out most of the sun. Breeding flocks could cover 40000 hectares (100,000 acres) with 100 nests built into each tree. With such high densities, market hunters could shoot or net the birds in very large numbers and fill train cars with harvested pigeons to be sold in eastern cities. This overharvesting, combined with the effects of forest clearing for agriculture, caused the passenger pigeon to decline quickly. The last passenger pigeon died in 1914 at the Cincinnati Zoo.
During the past century, regulations have been passed to prevent the overharvesting of plants and animals. In the United States for example, state and federal regulations restrict hunting and fishing of game animals particular times of the year and limit the number of animals that can be harvested. Similar agreements have been reached among countries through international treaties. In general, these regulations have proven very successful in preventing species declines caused by overharvesting. In some regions of the world, however, harvest regulations are not enforced and illegal poaching, especially of large, rare animals that include tigers, rhinoceroses, and apes, continues to threaten species with extinction. Harvesting rare plants, birds, and coral reef dwellers for private collections has also jeopardized the species.
Plant and Animal Trade
For some species, the legal and illegal trade in plants and animals represents a serious threat to their ability to persist in nature. One of the earliest laws in the United States to control the trade of wildlife was the Lacey Act. First passed in 1900, the act originally prohibited the transport of illegally harvested game animals, primarily birds and mammals, across state lines. Over the years, a number of amendments have been added so that the Lacey act today forbids the interstate shipping of all illegally harvested plants and animals.
At the international level, the United Nations convention on international trade in endangered species of wild fauna and Flora, also known as CITES was developed in 1973 to control the international trade of threatened plants and animals. Today, CITES is an international agreement among 182 countries throughout the world. The IUCN maintains a list of threatened species known as the Red List. Each member country assigned a specific agency to ensure and regulate the import and export of animals on the list. For example, in the United States, the U.S. Fish and Wildlife Service conducts this oversight.
Despite such International agreements, much illegal plant and animal trade still occurs throughout the world. In 2012, a report by the Congressional research service estimated that illegal trade in wildlife was worth 5 billion to 220 billion dollars annually. In 2017, it was estimated that 50,000 illegal shipments of wildlife and wildlife parts have been sent to United States ports over a 10-year period. In some cases, animals are sold for fur or for body parts that are thought to have medicinal value. For example, 1 kg of rhino horn can sell for $50,000. Other cases, rare animals are in demand as pets. For example, in 2001 a population of the Philippine forest turtle once thought to be extinct, was discovered on a single island in the Philippines. This animal, one of the most endangered species in the world, can not be traded legally, but demand for it as a pet has caused it to be sold illegally and the last remaining population has declined sharply in only a few years. A single turtle sells for $50 to $75 in the Philippines and up to $2,500 in the United States and Europe. Today, the turtle is critically endangered. Similar cases of illegal trade occur in rare species of trees for lumber such as big leaf mahogany, rare species of plants for medicinal use, and many rare species of orchids for their beautiful flowers.
Sometimes even when trade in a particular species is legal, it can pose a potential long-term threat to species persistence. In the southwestern United States, for example, there is a growing movement to reduce water used by replacing grass lawns with desert landscapes. One of the unintended consequences is increased demand for cacti and other desert plants that are collected from the wild. Sales are currently estimated to be $1 million annually. Given the slow growth of desert plants, this increased demand is causing height and concern for these plant populations in the wild.
The Endangered Species Act is designed to protect species from extinction. This act authorizes the US Fish and Wildlife Service to determine which species can be listed as threatened species or endangered species and prohibits the harming of such species, including prohibitions on the trade of listed species, their fur, or their body parts. IUCN threatened species have a high risk of extinction in the future and near threatened species are very likely to become threatened in the future. In the United States, an endangered species is defined as a species that is in danger of extinction within the foreseeable future throughout all or a significant portion of its range, whereas a threatened species is defined as any species that is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. The U.S. definition of endangered is similar to the international definition for threatened and the U. S.definition for threatened is similar to the international definition of near threatened.
The Endangered Species Act was first passed in 1973 and has been amended several times since then from the international perspective. The act also implements the international CITES agreement. To assist in the conservation of threatened and endangered species, the act authorizes the government to purchase habitat that is critical to the conservation of the species and to develop recovery plans to increase the population of threatened and endangered species. This is often one of the most important steps in allowing endangered species to persist. For example, grizzly bears in the greater Yellowstone ecosystem had 236 individuals in 1975. After being listed as endangered, steps were taken to protect the bear's favored habitat and today it numbers nearly 700 individuals.
As of 2018, the species that have been listed as threatened or endangered in the United States include 272 invertebrate animals, 442 vertebrate animals, and 947 plants. Although the listing process can take several years, once listed, many threatened and endangered species have experienced stable or increasing populations. In fact, some species have experienced sufficient increases in numbers to be removed from the endangered species list; these include the bald eagle, peregrine falcon, American alligator, and the Eastern Pacific population of the gray whale. Other species are currently increasing in number and maybe taken off the list in the future. The gray wolf, for example, was reintroduced into Yellowstone National Park to help improve the species abundance in the United States and it is now no longer endangered.
The Endangered Species Act has sparked a great deal of controversy in recent years because it can restrict certain human activities in areas where listed species live, including how landowners use their land. For example, some construction projects have been prevented or altered to accommodate threatened or endangered species. Organizations whose activities are restricted by The Endangered Species Act often try to pit the protection of listed species against the jobs of people in the region. In the 1990s, for example, logging companies wanted to continue logging the old growth forest of the Pacific Northwest. These forests are home to the threatened northern spotted owl and many other species that depend on old growth forest. Automation had caused a large decline in the number of logging jobs over the preceding several decades, and many loggers perceived the Endangered Species Act as a further threat to their livelihood. They denounce the act because they said it placed more value on the spotted owl than it did on the humans who depended on logging. In the end, a compromise allowed continued logging on some of the old growth forest while the rest became protected habitat.
During the past decade, several politicians and their constituents have attempted to weaken The Endangered Species Act. However, strong support from the public and scientists has allowed it to retain much of its original power to protect threatened and endangered species. The biggest current challenge is the lack of sufficient funds and personnel required to implement the law.