Student Science Journal

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6.4.4

Stability in Ecosystems

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Name ____________________

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Episode # 1 - Rabbits In Australia

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They may look cute and cuddly, but rabbits have been a persistent pest in Australia for more than 150 years. Rabbits are not a native species in Australian ecosystems. In 1859, a man named Thomas Austin introduced 24 wild rabbits to Australia for hunting in an attempt by early English colonists to make Australia similar to their European homeland. It was hoped that the rabbits would flourish so their owners could hunt them. And flourish they did. Facing very few native predators, rabbits spread across Australia.

Australia is an ideal location for the prolific rabbit. The winters are mild, so they are able to breed year-round. A single female rabbit can produce 18–30 babies per year. With few natural predators keeping their population in check, the number of rabbits exploded. By the 1920s, Australia’s rabbit population was 10 billion. Rabbits have adapted to Australia’s diverse environments, establishing themselves in farmland, deserts, grasslands, and wet coastal plains. So what’s the problem?

Rabbits love to eat seedlings and baby plants and will graze on native shrubs until the shrubs are completely unable to regenerate. Rabbits don’t harm giant trees, but they will eat every young seedling, so when the mature tree eventually dies naturally, there are no young trees to replace it. This causes the plant population to become unstable and shrink over time. When rabbits remove most of the plant life in an area, the entire structure of vegetation in an area can be altered. This loss of natural vegetation affects native species who rely on native plants for their diet. Rabbits also eat planted crops and compete with livestock for pasture. Soil erosion becomes a problem. Plants help hold soil in place, so when they’re gone, the land becomes dry and dusty, and rain can wash soil away.

They threaten Australia’s native burrowing animals such as the bilby and the burrowing bettong by moving into their existing burrows and competing for the same food resources. Forcing these animals to move or die. As native animal populations go down, the balance in the ecosystem changes even more.

Wild rabbits are an important part of the diet of cats and foxes, and their great numbers sustain these predator populations. These predators also feed on native mammal species, and their higher than usual numbers have caused Australia to lose more native mammal species than any other country.

Rabbits have changed Australia’s ecosystem in many ways. Changes to both the living and non-living parts of an environment can cause instability in many populations. This example shows how ecosystems are connected like a web, when one-part changes, the rest can be affected too.

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How have rabbits affected the stability of Australia’s ecosystems? Use specific examples from the article.

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Episode # 2 - Sea Otters

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Sea Otters and the Kelp Forests of the Pacific Coast

The kelp forest is a forest, but it is not a forest of trees. It is an underwater forest made of giant seaweed called kelp. Giant kelp grows in the cool, coastal waters and rocky shorelines of the Pacific Coast from Alaska to Baja, California. Kelp grows best in clear waters where sunlight can reach the ocean floor. In ideal conditions, kelp can grow up to 18 inches a day and can grow to heights of 150 feet. These underwater towers of kelp provide food and shelter for thousands of fish, invertebrates, and marine mammal species. Kelp forests harbor a greater variety and higher diversity of plants and animals than almost any other ocean community. The many mammals and birds that use kelp forests for protection or feeding include seals, sea lions, whales, sea otters, gulls, terns, snowy egrets, great blue herons, cormorants, and shorebirds. Besides supporting a huge amount of marine life, kelp forests protect coastlines from storm surge, help reduce coastal erosion, and absorb vast amounts of harmful carbon dioxide from the atmosphere. Similar to forests found on land, kelp forests use carbon dioxide during the process of photosynthesis, which produces energy for the plant and releases oxygen back into the air. Kelp is especially efficient at absorbing carbon dioxide.

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Sea otters and sea urchins are particularly important to the health and stability of kelp forests. Sea otters are considered a keystone species—one that plays a critical role in maintaining the health of its ecosystem. Sea otters’ favorite food is the sea urchin, which is a spiky, slow-moving plant-eating animal. Sea urchins like kelp—a lot—and, if their populations gets too big, they may graze a kelp forest to death; if they remain, they may also inhibit the kelp's ability to grow again in that area. Sea otters like sea urchins—a lot—which is a good thing because they can keep the urchin population under control, thus helping to preserve the kelp forests.

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Sea otters have beautiful, soft pelts and were hunted almost to extinction by fur traders in the 18^th and 19^th centuries. The fur trade halted abruptly with the International Fur Seal Treaty of 1911, which finally banned commercial harvesting. Sea otter populations were so completely decimated it was believed that they were extinct until a small population was found off the coast of California in 1938. The loss of sea otters from the kelp forest ecosystem of the Pacific Northwest resulted in the population of sea urchins growing unchecked. Without their natural predators around, sea urchin populations multiplied, forming herds that swept across the ocean floor devouring entire strands of kelp and leaving “urchin barrens” in their place. Little life could be found in a space that was once home to a diverse and complex ecosystem.

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With a ban on hunting and many conservation programs in place, the sea otter population has begun to recover, resulting in kelp forests growing once again and the reestablishment of the kelp forest ecosystem.

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Communicate- How are sea otters a keystone species affecting the stability of the kelp forest ecosystem?

Episode # 3 - Wolf Survival

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__________ & _________’s Data Table

Without Human Interference

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Total Wolves in Pack after 15 years: ___________�

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__________ & _________’s Data Table

With Human Interference

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Total Wolves in Pack after 15 years: ___________�

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Wolf Survival

Information Sheet

Simulation 1: Without Human Interference

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Simulation 2: With Human Interference

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What evidence do you have to support whether humans actions affect wolf populations.

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1. How was the stability of the wolf pack population affected by human interference in their ecosystem? Use evidence from the simulation to support your answer.

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2. How could this simulation relate to stability of actual ecosystems?

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Episode # 4 - The Lesson of the Kaibab

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The Kaibab Plateau is located in Northern Arizona. It is bordered on the south by the Grand Canyon and on the west and east by tributaries of the Colorado River. It is a heavily forested area home to turkeys, squirrels, bobcats, and deer.

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Before 1905, the deer on the Kaibab Plateau were estimated to number about 4,000. The average carrying capacity of the range was then estimated to be about 30,000 deer. The carrying capacity of an ecosystem is the maximum number of organisms that an area can support on a sustained basis. On November 28, 1906, President Theodore Roosevelt created the Grand Canyon National Game Preserve to protect the “finest deer herd in America.” The plan was to protect and expand the herd.

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Unfortunately, by 1905, the Kaibab forest area had already been overgrazed by sheep, cattle, and horses. Most of the tall grasses had been eliminated. The first step to protect the deer was to ban all hunting. Another step was to eliminate all predators. Between 1907 and 1939, 816 mountain lions, 20 wolves, 7,399 coyotes and more than 500 bobcats were killed.

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The Kaibab deer population began to experience a great increase in numbers. Signs that the deer population was out of control began to appear as early as 1920. The grazing range began to deteriorate rapidly. By 1923, the deer were reported to be on the verge of starvation and the range conditions were described as “deplorable.”

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Scientists recommended that the deer population be cut in half as quickly as possible. Hunting was reopened, and during the fall of 1924, 675 deer were killed by hunters. This only represented one-tenth of the deer that had been born that spring. Over the next two winters, it is estimated that 60,000 deer starved to death.

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Today, the Arizona Game Commission carefully manages the Kaibab area. Hunting permits are issued to keep the deer in balance with their range. Predators are protected to help keep herds in balance with food supplies.

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Graph the deer population data. Be sure to add a title and label your y- and x- axis.

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1. During 1906 and 1907, what methods were used to protect the Kaibab deer? Were these methods successful? Use data from your graph to support your answer.

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• Why did the population decline in 1925 even though predators had been eliminated? Think about both living and nonliving components within the ecosystem.

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3. Many ecologists have claimed that the population patterns would have occurred even if predators had remained in the habitat. Do you agree or disagree with this statement? Explain your reasoning.

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• How did human behavior affect the stability of the Kaibab plateau ecosystem?

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• What future management plans would you suggest for the Kaibab deer herd?

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6. Read each of the following statements. Evaluate the statement with examples from the Kaibab Plateau deer story.

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Living things tend to reproduce in numbers greater than their habitat can support.

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A population tends to increase in size until limited by one or more factors.

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Carry capacity may vary from season to season and from year to year.

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Carrying capacity stability may be affected by human actions.

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Carrying capacity stability may be affected by wildlife behavior.

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The most intense competition is between members of the same species.

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Construct an explanation to describe if the conservation methods were successful in stabilizing the deer population.

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Communicate:

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Construct an explanation to describe what caused the deer population to change and what role human interference played in changing the deer population. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Episode # 5 - Endangered Species

of Utah

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What patterns do you see in the endangered species in Utah?

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How can living and nonliving components in an ecosystem affect the stability of populations in that ecosystem? Use examples from the class presentations in your answer.

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