Chapter 23 - Living Resources

Section 1 - Environmental Issues

  Environmental issues fall into three general categories: resource use, population growth, and pollution. Anything in the environment that is used by people is a natural resource. Some natural resources, called renewable resources, are either always available or are naturally replaced in a relatively short time. Renewable resources include sunlight, wind, and trees. Resources that are not replaced as they are used are called nonrenewable resources. Examples include coal and oil. The use of nonrenewable resources is a problem because the supply may eventually be used up.

  Earth's human population grew very slowly until about A.D. 1650. Then improvements in medicine, agriculture, and sanitation began to enable people to live longer. The death rate decreased. But as the human population grows, it uses more resources and produces more waste.

  The contamination of Earth's land, water, or air is called pollution. Pollution is an issue because it is often the result of an activity that benefits humans.

  Dealing with environmental issues means making decisions. Decisions can be made at personal, local, national, or global levels. When personal choices made by millions of people are considered together, they can have a huge impact.

  Environmental science is the study of the natural processes that occur in the environment and how humans can affect them. But the data provided by environmental scientists are only part of the decision-making process. Decision makers must consider the needs and concerns of people with many different viewpoints. To help balance the different opinions on an environmental issue, decision makers weigh the costs and benefits of a proposal. Costs and benefits are not measured only in terms of money. Natural beauty, health benefits, and short-term and long-term effects are also considered.

Section 2 - Forests and Fisheries

  Forests are an important living resource. Trees and other plants produce oxygen that other organisms need. They also absorb carbon dioxide and many pollutants in the air. Forests help prevent flooding and control soil erosion. Many products come from forest plants.

  Because new trees can be planted to replace trees that are cut down, forests can be renewable resources. There are two major methods of logging. Cutting down all the trees in an area at once is called clear-cutting. Cutting down only some trees and leaving a mix of tree sizes and species behind is called selective cutting. Clear-cutting is usually quicker and cheaper than selective cutting. However, selective cutting is usually less damaging to the forest environment. When an area of forest is clear-cut, the habitat changes. Clear-cutting also exposes the soil to wind and rain.

  Forests can be managed to provide a sustainable yield. A sustainable yield is an amount of a renewable resource such as trees that can be harvested regularly without reducing the future supply. One sustainable approach is to log small patches of forest in stages. This way, different sections of forest can be harvested every year.

  A fishery is an area with a large population of valuable ocean organisms. If a fishery is managed properly, it can be a valuable renewable resource. But if fish are caught at a faster rate than they can breed, the population decreases. This situation is called "overfishing."

  Managing fisheries for a sustainable yield includes strategies such as setting fishing limits, changing fishing methods, developing aquaculture techniques, and finding new resources. Laws can help protect fish species by limiting the total amount of fish that can be caught or by setting a minimum or maximum size for the fish. A fishery may be closed until the fish populations recover. Nets with larger holes can be used to allow young fish to escape. Fishing methods that kill all the fish in an area can be outlawed. Aquaculture is the practice of raising fish and other waterdwelling organisms for food. Another way to help feed a growing human population is to fish for new species.

Section 3 - Biodiversity

  The number of different species in an area is called its biodiversity. There are many reasons why preserving biodiversity is important. Wild organisms and ecosystems are a source of beauty and recreation. In addition, biodiversity has both economic value and ecological value within an ecosystem. Organisms also provide food, oxygen, and raw materials for clothing, medicine, and other products. All the species in an ecosystem are connected to one another. A species that influences the survival of many other species in an ecosystem is called a keystone species.

  Factors that affect biodiversity in an ecosystem include area, climate, and diversity of niches. Tropical rain forests are the most diverse ecosystems in the world. The climate makes food available for organisms year-round. Tropical coral reefs are the second most diverse ecosystems in the world. A reef provides many different niches for organisms.

  A healthy species has a variety of traits, which are determined by genes. Genes are the structures in an organism's cells that carry its hereditary information. Each organism in a species has some genes that differ from the genes of other individuals in that species. These differences make up the gene "pool" of that species. A species with a diverse gene pool is better able to resist diseases and parasites and survive disturbances such as drought.

  The disappearance from Earth of all members of a species is called extinction. Species in danger of becoming extinct in the near future are considered endangered species. Species that could become endangered in the near future are considered threatened species. Natural events such as earthquakes can cause species to become extinct. Human activities can also threaten biodiversity. These activities include habitat destruction, poaching, pollution, and introduction of exotic species. The leading cause of extinction is habitat destruction, the loss of a natural habitat. Breaking larger habitats into smaller, isolated pieces or fragments is called habitat fragmentation. The illegal killing or removal of wildlife from their habitats is called poaching. Some species are endangered because pollutants build up in organisms through the food chain. Introducing exotic species into an ecosystem can also threaten biodiversity.

  Three successful approaches to protecting biodiversity are captive breeding, laws and treaties, and habitat preservation. One scientific approach is captive breeding, which is the mating of animals in zoos or wildlife preserves. Laws and treaties can help protect species by making it illegal to sell endangered species or products made from them. The most effective way to preserve biodiversity is to protect whole ecosystems.

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