Contents

^r/Bruce Coleman, Inc./PictureQuest

Habitat Loss In the Launch Lab at the beginning of this chapter, you probably observed that lawns and sidewalks have a lower biodiversity than sunlit woods or weed-covered lots. When people alter an ecosystem, perhaps by replacing a forest or meadow with pavement or a lawn, the habitats of some species may become smaller or disappear completely. If the habitats of many species are lost, biodiversity might be reduced.

Habitat loss is a major reason why species become threatened or endangered, as shown in Figure 9, or extinct. The Lake Erie water snake, shown in Figure 10, is classified as a threatened species because of habitat loss. These snakes live along the rocky shores of islands in Lake Erie. The islands are popular recreation spots. The development of boat docks and buildings in these areas has seriously reduced the amount of habitat available to the snakes. Also, these snakes are often killed by people who mistakenly think they are poisonous. Adult snakes range from 0.5 m to 1.0 m long, and they feed on fish, frogs, and salamanders. Because they have sharp teeth for capturing prey, they can bite. However, they are not dangerous to humans, especially if left undisturbed.

Conservation strategies for protecting the Lake Erie water snake include preserving its habitat by limiting development in some areas. Also, a public education program has been developed to inform people about this predator species and its importance in the Lake Erie ecosystem.

Figure 10 The Lake Erie water snake has become a threatened species.

Demonstrating Habitat Loss

Procedure

1. Put a small piece of banana in an open jar. Set the jar indoors near a place where food is prepared or fruit is thrown away.

2. Check the jar every few hours. When at least five fruit flies are in it, place a piece of cloth or stocking over the top of the jar and secure it with a rubber band.

3. Count and record the number of fruit flies in the jar every two days for three weeks.

Analysis

1. Explain why all the flies in the jar eventually die.

2. Use your results to hypothesize why habitat loss can reduce biodiversity. f at |

Vttome i

The building of boat docks, roads, and shopping centers is reducing the snake's habitat.

Figure 10 The Lake Erie water snake has become a threatened species.

The building of boat docks, roads, and shopping centers is reducing the snake's habitat.

Fear Snakes Explained

These snakes are not dangerous to humans, but many are killed by people who fear snakes.

SECTION 1 Biodiversity E ♦ 133

m/The Image Finders, (r)Melissa Hathaway/Ohio Dept of Natural Resources Division of Wildlife

These snakes are not dangerous to humans, but many are killed by people who fear snakes.

SECTION 1 Biodiversity E ♦ 133

m/The Image Finders, (r)Melissa Hathaway/Ohio Dept of Natural Resources Division of Wildlife

Figure 11 Introduced species can reduce or eliminate populations of native species in an ecosystem.

Figure 11 Introduced species can reduce or eliminate populations of native species in an ecosystem.

The ruffe was introduced into the Great Lakes by ships from other parts of the world. It quickly takes over habitat and food sources used by native fish.

Purple loosestrife was brought to North America from Europe and Asia in the 1800s. Dense patches of loosestrife grow and crowd out the native plants that some animals need for food and shelter.

Divided Habitats Biodiversity can be reduced when a habitat is divided by roads, cities, or farms. Small patches of habitat usually have less biodiversity than large areas. One reason for this is that large animals like mountain lions and grizzly bears require hunting territories that cover hundreds of square kilometers. If their habitat becomes divided, they are forced to move elsewhere.

Small habitat areas also make it difficult for species to recover from a disaster. Suppose a fire destroys part of a forest, and all the salamanders living there are destroyed. Later, after new trees have grown, salamanders from the undamaged part of the forest move in to replace those that were lost. But what if fire destroys a grove of trees surrounded by parking lots and buildings? Trees and salamanders perish. Trees might grow back but the salamanders might never return, because none live in the surrounding paved areas.

Introduced Species When species from another part of the world are introduced into an ecosystem, they can have a dramatic effect on biodiversity. An introduced species is a species that moves into an ecosystem as a result of human actions. Introduced species often have no competitors or predators in the new area, so their populations grow rapidly. Introduced species can crowd out or consume native species. Native species are the original organisms in an ecosystem.

In the early 1800s, European settlers brought goats with them to Santa Catalina Island off the coast of California. The goats overgrazed the land, completely eliminating 48 of the native plant species and exposing patches of bare soil. The bare soil provided a place for hardy, introduced weeds to take root. The weeds crowded out native species. Late in the twentieth century, after goats were removed from the island, some native plant species began to recover. Figure 11 shows introduced species that have reduced biodiversity in other ecosystems.

The ruffe was introduced into the Great Lakes by ships from other parts of the world. It quickly takes over habitat and food sources used by native fish.

Yourself Rain Chain

134 ♦ E CHAPTER 5 Conserving Life

(t)University of Minnesota Sea Grant Program, (b)Marcia Griffen/Earth Scenes

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