Reading Essentials for Biology Glencoe (794133), страница 13
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Where is the most biodiversity found?________________________________________________________________________44Chapter 5Biological diversity is also called biodiversity. Biodiversity refersto all the different species in a specific area. The most commonway to measure biodiversity is to count all the species in a certainarea. For example, an area of farmland might grow one type ofcorn. It might also contain hundreds of species of insects and several species of birds and other animals. The same size area of tropical rain forest might include hundreds of different types of plants,thousands of different insects, and hundreds of different types ofbirds. The rain forest has a greater biodiversity than the cornfieldbecause it has a greater number of species in the same area of space.Areas of the world that have the highest biodiversity are thosefound in warm, tropical places near the equator.
Such placesinclude rain forests, coral reefs, and tropical lakes.What do biodiversity studies tell us?Studying Biodiversity For many years, ecologists have studiedthe plants and animals on islands to learn more about biodiversity.In one study, scientists chose some small islands and counted thespiders and insects on the islands. Then they removed all speciesfrom the islands except for the trees.
This is what they found.(1) Insects and spiders returned first. (2) The farther the islandwas from the mainland, the longer it took for the species to moveback. (3) Eventually, the islands had about the same number ofspecies as they had in the beginning. However, some of the specieswere different. They also found that for the most part, the largerthe island, the more species that live on it.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Biological DiversityNameDateClassSection5.1Vanishing Species, continuedBiodiversity research is not easy.
Somescientists work for weeks at a time hundreds of meters off the ground in trees inrain forests. Others work counting all thespecies that live in coral reefs. Still otherswork in labs studying the DNA of membersof different populations. They look to seehow or if these populations are changing.Importance of BiodiversityAll living things are interdependent. This means they depend onother living things to stay alive.
For example, animals need plantsto survive. Most animals either eat plants or eat other animals thateat plants. Also, many plants need animals to survive. Some plantspecies, for instance, need bees or other animals to take their pollenfrom one plant to another so that the plants can reproduce. Thisis just one example of how plants need animals to survive.2. What does it mean to saythat all living things areinterdependent?________________________________________________________________________Copyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How do species depend on each other?Species that live together in the same area often depend oneach other.
They form symbiotic relationships. Symbiotic relationships, you will remember, are close, permanent, dependentrelationships between two or more organisms of different species.Because of this dependence, when one species permanently disappears, it affects the species that remain. An organism suffers whena plant or animal it feeds upon is permanently removed from afood chain or food web. A population may exceed the area’s carrying capacity if its predators are removed.Biodiversity Brings Stability Biodiversity can bring stability toan ecosystem.
Compare the following ecosystems.Low BiodiversityCornfield with only one speciesof corn is attacked by pests.All of the corn is destroyed.High BiodiversityRain forest with thousands ofdifferent species is attacked by pests.One species is destroyed. Otherspecies survive.Cornfields contain only one type of plant.
Therefore, biodiversity is low and the ecosystem may not remain stable if there is achange in species. Rain forests have many types of plants. Theyhave high biodiversity, which means the ecosystem could remainstable even if there is a change in species.READING ESSENTIALSChapter 545NameDateClassSection5.1Vanishing Species, continuedImportance to People Humans also depend on other organisms.People rely on plants and animals for food.
People also relyon plants for wood, cotton, and many types of medical drugs.These are just a few examples of how people depend on animalsand plants.If biodiversity continues, people will always have a supply ofliving things. One day, drugs to cure cancer or HIV might evenbe found in some of these living things.Loss of BiodiversityBiodiversity can be lost when species become extinct.
Extinction(ek STINGK shun) is the disappearance of a species when the lastof its members dies. A certain amount of natural extinction goeson all the time. But now it seems that more than usual is occurring. This could be due to a difference between human needs andavailable resources.A species is considered to be an endangered species whenits numbers become so low that extinction is possible. When aspecies is likely to become endangered, it is called a threatenedspecies. African elephants are one example of a threatened species.The complex interactions among species make each ecosystemunique.
Within each ecosystem every species is usually well adaptedto its specific habitat (the place where a species lives). This meansthat changes to a species’ habitat can threaten the species withextinction. In fact, habitat loss is one of the biggest reasons fordecline in biodiversity.3. What is habitatfragmentation?________________________________________________________________________46Chapter 5Habitat Loss One example of habitat loss is in the Amazonianrain forest. In the 1970s and 1980s, thousands of hectares ofland were cleared for firewood and farming. Clearing the landdestroyed many habitats. None of them can be built up againeasily.
Without these habitats, some plants and animals maybecome extinct.How does habitat fragmentationaffect biodiversity?Habitat Fragmentation Another threat to biodiversity is habitatfragmentation. Habitat fragmentation is the separation ofwilderness areas from other wilderness areas. The fragmentedareas are similar to islands. They are cut off from other habitats.READING ESSENTIALSCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.Threats to BiodiversityNameDateClassSection5.1Vanishing Species, continuedFragmentation can cause species diversity to drop. This happens when some species leave an area that has become unsuitablefor them.
Then, other species that depend on these species alsoleave or die out. When species leave a fragmented area or die out,overall species diversity declines.Habitat fragmentation can cause members of the same speciesto become separated from each other. Some members get stuck inone fragmented area while others get stuck in another. Then thetwo populations cannot interact. This means that the members ofone population cannot breed with members of the other population. Genes from one population cannot mix with the genes fromanother. This is known as genetic isolation.Edge and Size The edge of a habitat is where one habitat meetsanother.
A forest meeting a field or a road cutting through a forest are two examples of edges. Conditions along the edges aredifferent than they are in the middle of a habitat. These differentconditions are called edge effects. Because of the different conditions, different organisms may live at the edge of a habitat than inthe middle of a habitat.4. Interpret Which diagramdemonstrates habitatfragmentation? (Circleyour choice.)a.PopulationAPopulationBb.Population PopulationABCopyright © by Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.How does pollution affect the environment?Habitat Degradation Habitat degradation is another threat tobiodiversity. Habitat degradation is damage to a habitat causedby air, water, or land pollution.
Air pollution can cause breathingproblems. It can also irritate the eyes and nose. Acid precipitation—rain, snow, sleet, and fog with low pH values—has damagedsome forests, lakes, statues, and buildings. Acid precipitationforms when pollutants in the air combine with water vapor in theair. When these acidic droplets hit Earth, the moisture takesnutrients out of the soil. Without the nutrients, many plantsbecome sick and die.The Sun gives off waves, called ultraviolet waves, which candamage living things.
Earth has an area in its atmosphere,between 15 km and 35 km altitude, called the ozone layer, whichabsorbs some of these ultraviolet waves before they reach Earth.Pollution has damaged the ozone layer. Today more ultravioletwaves reach the Earth than in the past. Over some parts ofAntarctica, the amount of ozone overhead is reduced by as muchas 60 percent during the Antarctic spring.
This seasonal reductionof ozone is caused by chemicals such as chlorofluorocarbons(CFCs), which are produced by humans.READING ESSENTIALS5. Why do more ultravioletwaves reach Earth today?________________________________________________________________________Chapter 547NameDateClassSectionVanishing Species, continued6. Conclude Which of thefollowing does notthreaten biodiversity?(Circle your choice.)a. acid rainb. rain forestsc.
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