Factors that Threaten Biodiversity. How has Overexploitation Caused Extinction? Lesson 4. Chapter 3 Ecosystems: Interactions, Energy and Dynamics

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1 Chapter 3 Ecosystems: Interactions, Energy and Dynamics Lesson 4 Threats to Biodiversity and Conserving Biodiversity Main idea: Biodiversity maintains a healthy biosphere. Some human activities threaten biodiversity which can result in serious long-term effects. People are using a variety of different approaches to conserve biodiversity. Next Generation Science Standard -Performance Expectation MS-LS2-4 Construct an argument supported by evidence that changes to abiotic or biotic components of an ecosystem affect populations. MS-LS2-5 Evaluate competing design solutions for maintaining biodiversity and ecosystem services. What will you learn? Compare the ways in which ecosystem biodiversity is being threatened. Analyze how an invasive species, can impact an ecosystem Investigate and evaluate techniques humans use to preserve biodiversity. Why is it important? Learning the value of biodiversity to humans and how biodiversity is threatened will help you understand why it is necessary, and how it can be preserved. Vocabulary overexploitation eutrophication habitat loss introduced species habitat destruction sustainable use habitat degradation endemic habitat fragmentation hot spots edge effect bioremediation biological magnification biological acid precipitation augmentation Factors that Threaten Biodiversity The high extinction rate today is due to the activities of a single species Homo sapiens. Humans are changing conditions on Earth faster than new traits can evolve to cope with the new conditions. Evolving species might not have the natural resources they need. Natural resources are all materials and organisms found in the biosphere. Natural resources include minerals, fossil fuels, plants, animals, soil, clean water, clean air, and solar energy. How does overexploitation harm a species? One factor that is increasing the current rate of extinction is overexploitation. Overexploitation is the excessive use of a species that has economic value. For example, at one time, about 50 million bison roamed the central plains of North America. The bison nearly became extinct because of overhunting. By 1889, there were fewer than 1000 bison left. How has Overexploitation Caused Extinction? At one time, passenger pigeons were numerous in North America. Large flocks of birds flew in the skies. Passenger pigeons were overhunted and forced from their habitats. By the early 1900s, the birds had become extinct. Animals today that suffer from overexploitation include the ocelot, and the white rhinoceros. People kill ocelots for their fur and white rhinoceroses for their horns, which some cultures believe have medicinal purposes. 1

2 Figure 1. The passenger pigeon (middle) is extinct the ocelot (left) and white rhino (right) are nearing extinction, all due to overexploitation by humans. Why is Habitat Loss a Problem? Overexploitation was once the main cause of extinction, discussed in the lesson 3. Today, however, the main cause of extinction is habitat loss. The main types of habitat loss are habitat destruction, habitat degradation and habitat fragmentation. When a habitat loss occurs, the native species will either have to move, or somehow adapt, or they will die. If this happens in many areas where the organism exists, it may become extinct. Habitat destruction occurs when natural habitats are no longer able to support the species present, resulting in loss of the habitat s biodiversity. Examples include harvesting some fossil fuels, deforestation, dredging rivers, urbanization, filling in wetlands and mowing fields. Once this destruction occurs, the species inhabiting these areas must leave or they may die out, resulting in a loss of biodiversity. An example of habitat destruction occurs in tropical rain forests, and can be caused by man or by natural causes. Man might need wood from the trees, or need to clear land to grow food crops. Or a forest fire might be ignited by a lightning strike. When these things happen, habitat is destroyed. The organisms that lived there must migrate or may become extinct. The Hyacinth Macaw is one of 17 species of macaws, living in rainforests, which are endangered due to habitat destruction. Loss of tropical rain forests is a serious threat. Remember, that tropical areas have high levels of biodiversity. More than half of the world s plants and animals live in tropical rain forests. Removal of these forests would cause high numbers of extinctions, reducing biodiversity. Also remember that with these extinctions we lose plants and animals that may have provided some benefit to us, but we may have not discovered it yet! Once these organisms are gone, we will never have access to them again. 2

3 Figure 2. Species often become vulnerable to extinction when their web of ecological interactions becomes seriously disrupted by habitat degradation. When habitat degradation (also called disruption of habitat), occurs, the habitat may remain intact, but its degraded state keeps it from functioning properly this might lead to species extinction or migration. The main causes of habitat degradation are pollution, invasive species, agricultural development, urban sprawl, logging, mining, destructive fishing practices and the disruption of ecosystem processes. Habitat degradation can occur from changing just one thing in a habitat. Figure 2 shows an example of how the decline of one species can cause a chain reaction that affects an entire ecosystem. This chain of events occurred off the coast of Alaska in the 1970s when plankton-eating whales began to disappear, and altered the balance of fish in the ocean ecosystem, resulting in killer whales feeding on sea otters. As whale numbers declined, their food, ocean zooplankton, became overly abundant. Given this ample food supply, the Pollock fish reproduced and outcompeted other fish like herring and ocean perch for this food source. This led to fewer numbers of herring and perch. Additionally, commercial fishermen were overfishing perch and herring at this time. Pollock, now numerous in the ecosystem, were less nutritious as a food source for sea lions and seals that fed on them. Because they did not provide sufficient nourishment sea lion and seal numbers fell dramatically. As you know, seals and sea lions are the major food of orcas, also called killer whales. Faced with a food shortage, some killer whales started eating sea otters. In one bay where the entrance was too narrow and shallow for orcas to enter, only 12% of the sea otters have disappeared, while in a bay where orcas could enter, two thirds of the otters disappeared in a year's time. 3

4 Without otters to eat them, the population of sea urchins in the ecosystem exploded, eating the kelp and so "deforesting" the kelp forests. As a result, fish species that live in the kelp forest, like sculpins and greenlings (a cod relative), will probably decline, and local populations of bald eagles, totally dependent on these fish populations, were expected to drop off sharply. Commercial whaling appears to have initiated a series of changes that have led to orcas beginning to feed on sea otters, with disastrous consequences for their kelp forest ecosystem. As this example explains, species often become vulnerable to extinction when their web of ecological interactions becomes seriously disrupted. Figure 3 An example of how edge effect reduces contiguous territory. Habitat fragmentation is the separation of habitats into small areas as shown in Figure 3. Species stay in the small areas because they can t or won t cross the barriers. The 'cutting up' of habitats is mainly caused by agricultural land conversion, urbanization, dams and water diversions but can also be caused by geological processes that alter the layout of the environment. One organism impacted by habitat loss and fragmentation is the Florida panther. This beautiful large cat now occupies only a small area of South Florida, about 5 percent of its former range, and it numbers just 100 to 120 individual cats. Specifically fragmenting its range are the highways and urban development built to accommodate the people of Florida. Male Florida panthers, do not have large areas to roam now, because roads slash through panther habitat, also the great cats are killed through vehicle collisions. There are several specific problems created by fragmentation. First, small areas of land cannot support large numbers of species. Second, the fragments may not be large or connected enough to support species that need a large territory. Third, individuals in one area cannot reproduce with individuals in another area, causing genetic diversity to decrease. Less genetically diverse populations are less able to resist disease and adjust to environmental changes. Fourth, several small areas have more edges than one large area. Environmental conditions along the boundaries of an ecosystem are different, a factor known as the edge effect. Temperature, humidity, and wind are often different along the edge of a habitat than they are at its center. Species that are adapted to living in a specific environment will be less well adapted to living in on the edge environment, as the edge environment is slightly different. 4

5 How does Pollution impact Biodiversity? Pollution damages ecosystems and decreases biodiversity by releasing harmful substances into the environment. Pesticides and industrial chemicals are examples of pollutants that end up in food webs. These pollutants are mainly from activities carried on by humans, such as farming, mining and industrial manufacturing, as well as the burning of fossil fuels. Substances that are natural can become pollution when they are too abundant in a certain area. For example, nitrogen and phosphorous are important nutrients for plant growth, but when they concentrate in water systems after being applied as agricultural fertilizers, they can cause dead zones that are uninhabitable for fish and other wildlife. As plants absorb, and animals eat these substances in their food and water, the pollutants accumulate in their tissues. Animals that eat other animals are most affected by the buildup of pollutants. Biological magnification occurs when pollutants build up to high levels in bodily tissues of animals higher up on the food web - carnivores. The amount of pollutants might be relatively low when it enters the food web, but it increases as it spreads to a higher trophic level. The Bald Eagle and DDT (Dichlorodiphenyltrichloroethane) Although they primarily eat fish and carrion, people used to believe that bald eagles preyed on chickens, lambs, and domestic livestock. Consequently, the large raptors were shot in an effort to eliminate a perceived threat. Coupled with the loss of nesting habitat, bald eagle populations were declining in the 1940 s. Shortly after World War II, in 1945, DDT was being widely used as a new pesticide to control mosquitoes and other insects. However, DDT and its residues washed into nearby waterways, where aquatic plants and fish absorbed it. Bald eagles, in turn, were poisoned with DDT when they ate the contaminated fish. It was believed that the chemical interfered with the ability of the birds to produce strong eggshells. By the 1950 s there were only 412 nesting pairs in the 48 contiguous United States, down from an estimated 500,000 individuals in the late 1800 s. The Bald Eagle s egg shells were so thin that they often broke during incubation. DDT also affected the egg shells of other species such as peregrine falcons and brown pelicans. The numbers of Eagles were decreasing rapidly at this time. It was feared that our national bird might become extinct. As the dangers of DDT became known, the Environmental Protection Agency took the historic and, at the time, controversial step of banning the use of DDT in the United States, in That was the first step on the road to recovery for the bald eagle. The Eagle has made a successful recovery, now the 48 contiguous United States has almost 9,800 nesting pairs of eagles. 5

6 There is still some controversy as to whether the DDT caused this problem. Studies were done with chickens, where their egg shells did not thin, but was there something different about using a chicken? It was generally accepted that the DDT was the cause of the egg shell problem, but even among those not convinced, most agree it was a good idea to get this pesticide called DDT out of our food chain. Acid precipitation, also known as acid rain, is another pollutant that is affecting biodiversity. When fossil fuels are burned sulfur dioxide is released into the air. In addition the burning of fossil fuels in automobiles engines releases nitrogen oxides into the atmosphere. These compounds react with water and other substances in the air to form sulfuric acid and nitric acid. These acids eventually fall to the surface of the Earth in rain, sleet, snow, or fog. Acid rain does not usually kill trees directly. Instead, it is more likely to weaken the trees by damaging leaves, limiting nutrients available to them, or poisoning them with toxic substances slowly released from the soil. Acid precipitation removes calcium, potassium and other nutrients from the soil, depriving plants of these nutrients, which damages plants and slows their growth. Figure 4 An acid rain poisoned forest area. Acid buildup in lakes and Rivers. Sometimes the acid concentration is so high in lakes, rivers and streams that fish and other organisms die. Most lakes and streams have a ph between 6 and 8, see Figure 5. Organisms that live there have adapted to survive in this environment. However, when acid rain falls on to the Earth and runs into lakes and streams or falls directly onto lakes and streams, it lowers the ph (makes water more acidic) changing the organisms environment and they often cannot survive. Figure 5 The Ph scale 6

7 Eutrophication is another form of water pollution. It destroys underwater habitats for fish and other species. Eutrophication (yoo troh fih KAY shun) occurs when fertilizers, animal wastes and/or sewage flow into waterways. These substances are rich in nitrogen and phosphorus, and they cause algae to grow. The algae use up the oxygen supply during their rapid growth, and after their deaths during the decaying process. Other organisms in the water suffocate. Sometimes the algae release toxins that poison the water supply for other organisms. While eutrophication is a natural process, human activities have accelerated the rate at which it occurs. How do Introduced Species Impact Biodiversity? An introduced species (these also can be called alien species, exotic species, non-indigenous species, or non-native species) is a species living in an area that it DOES NOT naturally inhabit. They have arrived in a new ecosystem as a result of human activity, either deliberate or accidental. Accidental introductions occur when species are accidentally transported by humans. Increasing rates of human travel are providing many opportunities for species to be accidentally transported into areas in which they are not native. For example, three species of rat (the black, Norway and Polynesian) have spread to most of the world as hitchhikers on ships. Imported fire ants are a species that is believed to have been introduced to the United States through the port of Mobile, Alabama in the 1920 s by ships from South America. Fire ants spread throughout the southern and southwestern United States, as illustrated in Figure 6. Fire ants attack and feed on wildlife, such as newborn deer and hatching or newly hatched ground-nesting birds. Figure 6 Current area in the United States inhabited by a species of fire ant accidentally introduced in the 1920 s 7

8 When introduced species begin to live in a new area, they can upset the biodiversity in that ecosystem. These species are not a threat to the biodiversity of their own habitats. Predators, parasites, and competitive species keep their native ecosystem in balance. However, when they are introduced into a new area, these factors that keep the species in check, change. Introduced species often reproduce in large numbers, become predators, and become invasive species in their new habitats. Introduced species that become established and spread beyond the place of introduction are called invasive species. The impact of introduced species is highly variable. Some have a negative effect on a local ecosystem, while other introduced species may have no negative effect or only minor impact. An estimated 40 percent of the extinctions that have occurred since 1750 are due to introduced species, and billions of dollars are spent every year in an effort to clean up or control the damage caused by introduced species. According to the World Conservation Union, invasive alien species are the second most significant threat to biodiversity, after habitat loss. Figure 7 Purple loosestrife is a good example of an invasive organism. Look at the information at the left, what are several problems with this plant? Conserving Biodiversity People are using many approaches to slow the rate of extinctions and preserve biodiversity. Conserving natural resources, and repairing a damaged ecosystems are two things we will explore which are ways to preserve biodiversity. Natural Resources The biosphere provides the basic needs for over 7.2 billion people in the form of natural resources. The population continues to grow, which means more natural resources are necessary. Resources are not evenly distributed over the Earth, nor are they evenly consumed. Figure 8 shows the use of natural resources per person for selected countries. The natural resource use rate is much higher for people living in developed countries than for people in developing countries. As developing countries become more industrialized and the standard of living increases, the rate of using natural resources increases. Because of the rising human population growth and an increased rate of using natural resources, a long-term plan for the use and conservation of natural resources is important. 8

9 Renewable Resources Plans for long term use of natural resources must take into consideration the difference between the two groups of resources--renewable and nonrenewable resources. Renewable resources are those that are replaced by natural processes faster than as fast as, they are consumed. Solar energy is an example of a renewable resource. Agricultural plants, animals, water and air are considered renewable because normally they are replaced faster than they are consumed. However the supply of these resources is not unlimited. If the demand exceeds the supply of any resource, the resource might become depleted. Figure 8 The consumption, or use, of natural resources per person for selected countries. Nonrenewable Resources Nonrenewable resources are those that are found on the Earth in limited supply, they could be replaced by natural processes, but slower than they are used. Fossil fuels, mineral deposits and radioactive uranium are nonrenewable resources. Species are considered nonrenewable resources because an extinct species cannot be replaced. Sustainable Use One approach to using natural resources called sustainable use. Just as the name implies, sustainable use means using resources at a rate in which they can be replaced or recycled while preserving the long-term environmental health of the biosphere. Sustainable use includes reducing the amount of resources that are used, recycling, and using resources responsibly 9

10 Protecting Biodiversity As you know, human activities have affected many ecosystems. Many efforts are underway worldwide to slow the loss of biodiversity and to work toward sustainable use of natural resources. Protected Areas in the United States Conservation biologists recognize the importance of establishing protected areas where biodiversity can flourish. The United States established its first national part Yellowstone National Park in 1872 to protect the area s geological features. Many additional national parks (there are currently 58) and nature reserves have been established since International Protected Areas Many countries establish national parks or nature reserves. Currently about 7 percent of the world s land is set aside as some type of reserve, to protect biodiversity. Historically, protected areas have been small islands of habitat surrounded by areas that contain human activity. Because the reserves are small, they are impacted heavily by human activity. The United Nations supports a system of Biosphere Reserves and World Heritage sites. Costa Rica has established large reserves called megareserves. These huge reserves are protected from human activity by buffer zones an area in which sustainable use of natural resources is permitted. This approach creates a large managed area for preserving biodiversity while providing natural resources to the local population. Biodiversity Hot Spots Conservation biologists have identified locations around the world that are characterized by many endemic species species that are only found in that one location. These areas are called hot spots. To qualify as a hot spot, the area must have at least 1500 species of vascular plants that are endemic and the region must have lost at least 70 percent of its original habitat. The recognized hot spots are shown in Figure 9. About half of all plant and animal species are found in hot spots. These hot spots originally covered 15.7 percent of Earth s surface, however only about a tenth of that habitat remains. Biologists in favor of recovery efforts in these areas argue that focusing on a limited area would save more species, others argue that concentrating the funding in these areas does not address serious problems like restoring a wet lands. They argue for putting money into the wetlands area because the wetlands provides greater services for people by filtering water, as well are providing flood regulation and a nursery for fish. It is difficult to decide where to spend funds. Many biologists believe that funds should be spent in all areas of the world, rather than just focusing on the hot spots. 10

11 Figure 9 Biodiversity hot spots, highlighted in red on the map, are ecosystems where endemic species are threatened. If these species become extinct, biodiversity will decrease Corridors between Habitat Fragments Conservation ecologists are also focusing on improving the survival of biodiversity by providing corridors, or passageways, between habitat fragments. Corridors as shown in Figure 10 are used to connect smaller parcels of land. These corridors let organisms move safely between the two areas. Connecting the populations in this way encourages greater species diversity and genetic diversity, because the organisms from one area can pass to the other area. However, using this approach does nothing to reduce the problem of edge effect. Figure 10 Corridors. 11

12 Restoring Ecosystems Sometimes, biodiversity is destroyed because the biotic and abiotic factors needed for a healthy ecosystem are no longer present. Soil cleared from a tropical rainforest becomes unproductive for farming after a few years. After mining activities have ceased sometimes the land might be abandoned in such a way, that the native species cannot live there again. Accidental oil spills and toxic chemical spills might pollute an area to such a degree that the native species cannot live there. Given time, biological communities can recover from natural and human-made disasters, as illustrated in Figure 11. The length of time for recovery is not related directly to whether the disaster is natural or human-made. The size of the area affected and the kind of disturbance are the factors that determine recovery time. Scientists use two methods to speed the recovery of damaged ecosystems these are bioremediation and biological augmentation. Figure 11 Recovery times vary for different types of disasters 12

13 Bioremediation The use of living prokaryotes, fungi or plants, to detoxify a polluted area is called bioremediation. The organisms actually feed on the contamination and use it for growth and reproduction. In South Carolina in the mid 70 s a fuel storage facility leaked about 80,000 gallons of kerosene based jet fuel, which soaked into the sandy soil and contaminated the underground water table. Microorganisms that naturally are found in the soil break down these carbon-based fuels into carbon dioxide. Scientists found that by adding additional nutrients to the soil, the rate at which the microorganisms decontaminated the area was increased. In a few years, the contaminated in the area had been greatly reduced. These microorganisms can be used in other ecosystems to remove toxins from soil that are contaminated by accidental oil or fuel spills. Some species of plants are being used to remove toxic substances, such as zinc, lead, nickel, and chemicals from damaged soil as shown in Figure 12. These plants are planted in the contaminated soil, they take up the harmful toxins as they grow and store them in their tissues. The plants then are harvested, and the toxins are removed from the ecosystem. Geraniums can be used to clean the soil of poisons or toxins. Other plants such as pennycress and willow can remove cadmium, and zinc but it may take years. Bioremediation is relatively new, but the process shows great promise. Figure 12 Bioremediation uses living (bio) organisms to assist with cleaning the environment. These plants can remove toxins and metals from the soil. Pennycress Willow Geranium Biological Augmentation Biological augmentation involves the addition of selected living things (predators or microbes for example) to a degraded ecosystem. For example, aphids very small insects eat vegetables and other plants, which can result in the destruction of farm crops. Ladybugs are predators that eat aphids. Farmers can introduce ladybugs to help control insect populations in farm ecosystems. The Ladybugs do not harm the crops, and the fields are kept free of aphids. Scientists have also been able to add specific bacteria (microbes) to lakes and ponds with an overload of organic material (which can come from natural sources or human sources such as agricultural runoff). This addition will correct the balance of microbes in the area where natural microbes may have been destroyed or exist in low numbers. In this way, water quality is achieved through all natural means, without the addition of harsh chemicals. 13

14 Legally Protecting Biodiversity During the 1970 s people began to become more aware of environmental issues. As people became interested and research was funded, awareness of existing and possible environmental problems began to grow. In 1973 the Endangered Species Act was passed in the United States. It gives legal protection to species that are in danger of becoming extinct. In 1975 an international treaty was signed that outlawed the trade of endangered animals and animal parts, such as elephant tusks and rhinoceros horns. Since then, many more laws and treaties have been enacted with the purpose of preserving biodiversity and the health of the biosphere. Summary Historically, overexploitation of some species by humans has led to their extinction. Human activities, such as release of pollutants, habitat loss and the introduction of nonnative species, can result in a decrease in biodiversity. There are many approaches used to conserve biodiversity in the world. Two techniques used to restore biodiversity in an ecosystem are bioremediation and biological augmentation. Since the 1970 s, many forms of legislation have been passed to protect the environment. Self Check 1. Explain three ways that humans threaten biodiversity. 2. Summarize how the overharvesting on one species (such as the baleen whale) can affect an entire ecosystem. 3. What are the two kinds of natural resources? 4. Describe three approaches used to slow down the rate of extinction or to preserve biodiversity. 5. Analyze the advantages and disadvantages of large and small nature reserves. 14