Wildlife Diversity: The Links of Life

Chapter 1: Wildlife Populations

Have you ever wondered how many mice live in the log pile in your yard? How many mice inhabit the old leaning barn down the road? The number of animals in a specific area is called a population.

There are different ways of calculating a population. A common method is to take a census. A census is an exact count of every animal in a population. It's most accurate when the animals are easy to see and are found in limited areas.

Sometimes it's impractical to count animal populations, so managers sample populations instead. Sampling is not an exact count--it's an estimate. In a sample, animals in just a portion of the total area are counted. This number is then used to calculate an estimated total population. For example, a sample of ducks on a pond would be estimated by counting the ones on half the pond and doubling that number. Yearly population samples or census show if the wildlife population size is changing. This is important because if the population is decreasing, the habitat might need improvement or hunting might need to be restricted. If the population is increasing, hunting or food control might be increased.

A. How Does Your Population Grow?

Wildlife managers need to know how a population grows. To be able to measure they must know how many animals are added to or subtracted from the population each year. By knowing how quickly the population grows or shrinks, the future size of the population can be predicted.

Activity 1: Population in Your Neighborhood

• Notebook
• Pen or pencil
• Binoculars (optional)
• Record sheet
  (Appendix A).

1. Choose a kind of animal that lives in your neighborhood. Pick a type that is easy to watch, like robins, ants, squirrels, or people.
2. Decide on the size of the area you are going to sample from the study area. If you choose large animals, such as people, use your whole block.
3. Count the number of animals in your sample area. If you choose a small animal like an ant, use a 10-foot by 10-foot area. Now, multiply your count by two. Is this number close to the total population? Why do you think the numbers are different? Which number is more accurate? Which population count was easier to make?

World Population

The worlds population has doubled
every 40 years. From the past figures we
can predict future populations.

Activity 2: Turtle Town Tale

• Birth
• Immigration

Every time an animal is born, it's added to the population. The total number of animals born to a population each year can be counted or estimated.

Rodents such as mice may have about five babies in a litter and have several litters per year. On the other hand, elephants have just one young every two years. Painted turtles lay from two to twenty eggs a year, but they don't all survive to become adults.

Another event that increases population is immigration, or when animals move into a new area. Animals leave their homes to find new ones if their old habitat is too crowded, if they can't find a mate, or if their old habitat is destroyed. Leaving an old habitat is called emigration.

2. Two events decrease populations:

• Death
• Emigration

When an animal dies it is subtracted from the population. Animals die from old age, starvation, disease, predation, or accidents. Sometimes the beginning of life is the most dangerous because young animals are easier for predators to catch.

The original population in Turtle Town was 100 turtles. What is the population now? Did it increase, decrease, or stay the same?

The population was originally 100 and increased by 10 turtles.

There are now 110 turtles in Turtle Town, and the population is growing. What would the population be if there were:

• 50 births
• 50 turtles immigrated
• 100 died
• 20 emigrated

B. Carrying Capacity

A habitat is the place and conditions where an animal lives. Habitat provides the important needs of animal life: food, water, shelter, and space. But a specific area of habitat contains only limited supplies of these things and can support only a limited number of wildlife. Similarly, the earth can only support a certain number of people (although experts disagree on the estimated number, many estimate 15 to 20 billion). This number is the earth's carrying capacity. When a habitat's carrying capacity is exceeded, either the environment or the wildlife is harmed.

The carrying capacity of a habitat for wildlife often decreases in winter when there is less food and cover. In spring, when most animals are born, it increases as more food becomes available.

Turtles hatch out in late summer, which is a difficult time for turtles in Turtle Town because there usually is less water available. Small ponds dry up and larger ones shrink as the summer passes. The carrying capacity of an area may be the lowest for turtles at this time.

If there are more turtles than the carrying capacity of the habitat, some will have to leave the area or they will die.

Fill in the blank next to each description with one or more of the four parts of the growth equation (birth, death, immigration, emigration) that you think will most likely happen to the turtle pond described.

Pond A being filled  _________________________________ _________________________________________________

Pond B drying up  __________________________________ _________________________________________________

Good food in pond C  _______________________________ _________________________________________________

C. Predators and Prey

Did you know that robins are predators? After rain, robins search grassy areas for worms. In the evenings, bats swiftly stalk insects. Hawks soar through the sky searching for mice to eat. Many animals hunt and kill other animals to eat. These animals are predators. The animals that are killed and eaten are called prey.

Which came first, the chicken or the egg? Predators and prey influence each other. If a prey population is high, more predators survive because they have more food. The carrying capacity for the predators increases. As the number of predators increases, they eat more and more prey and prey numbers drop. The carrying capacity of the predator then may decrease because they have over- hunted the area.

Activity 4: Who Preys with Whom? Fill in the chart below of predators and prey. Add at least three new predator/prey relationships. Predators Prey/Predator Prey   Hawk   Squirrels   Nuts   Robin   Worms   Soil   Mice   Grasshoppers   Moose   Mosquitoes

D. Linked Together

All forms of life are interconnected in "links of life." Predators depend on prey, and prey, in turn, depend on other prey or plants for food. Even plants need insects and animals to pollinate them. Some links are simple and some are complex. Each time a part of the link disappears, the system changes and becomes less stable. If an important link disappears, the whole system may even fall apart. A healthy environment is one that has all of its parts.

People also are part of the "links of life," and we depend on many other life forms for our survival. Plants produce oxygen that we need to breathe. Bacteria help to decompose the wastes we produce. Medicines often come from wild plants and animals.

A Caution to Everybody Consider the auk; Becoming extinct because he forgot how to fly, and could only walk. Consider the man, who may well become extinct Because he forgot how to walk and learned how to fly before he thinked.    - Ogden Nash From: I Wouldn't Have Missed It. Selected Poems of Ogden Nash. Boston and Toronto: Little, Brown and Company (Canada) 1975.

Activity 5: The Food Chain Draw a picture of what you ate for breakfast this morning. Now try to trace your food back to its original sources. Try to list at least one other animal that might use the sources of your food. For example: 1. Eggs-chicken-fox 2. Toast-flour-wheat-beetle 3. Jelly-sugarcane plant 4. Apple jelly-apple tree-worms Do the same thing for lunch and dinner. Breakfast Lunch or Dinner

E. Population Cycles

A population cycle happens when populations of animals show a regular pattern of population increases and decreases. You can see how this works by graphing a white-tailed deer cycle in Activity 6.

Ducks, pheasants, songbirds, and many other animals have cycles that fluctuate up and down. An annual (yearly) population cycle mostly occurs in wildlife that have young only once a year. Turtles, mice, and some birds have young several times a year and do not have this same pattern of population change.

Some animals have population cycles of several years as well as an annual cycle. For example, ruffed grouse populations have a cycle of about 10 years. The population may start out low, then become high, and finally after 10 years be low again. No one is certain why these populations cycle like this. There are probably many factors involved, including weather, disease, predators, and food sources. And not all animal groups cycle in a particular way.

Although humans reduce wildlife populations through hunting, not all human activity reduces animal populations. In some cases, animals are introduced into an area to increase the population. When game animals are added to the population every year, it is called stocking. Pheasants, quail, and a variety of fish are stocked in the Lake States. When animals are brought back to an area where they once lived, it is called a reintroducing. Moose, peregrine falcons, trumpeter swans, and wild turkeys have been reintroduced into the Lake States. Can you think of some situations when reintroducing would be a good wildlife management practice? Situations in which it would be bad?

In winter, many deer die and the population is low because of cold weather and limited food supply. In the spring, when fawns are born, the population increases. Put an x on the line for spring at a high level. During the summer, most deer are healthy, but many young animals are vulnerable and die from predation. Put an x on the line for summer between medium and high population levels, and put an x for winter at the low population level. Draw a line connecting the x's to plot the yearly change in population.

Wild Fact White-tailed deer in Minnesota There are about a million deer in Minnesota. On average, deer live to be 7 to 15 years old. Of course, in areas of the state where hunting is high and winters are severe, the average life span is much less. Deer populations cycle every several years, but no one is really sure why. In the 1970s, in northern Minnesota, the deer population took a nosedive. Biologists believe that several severe winters in a row, increased hunting, and an increase in the number of wolves were responsible for this population crash.

F. Extinction-The Land of No Return

Extinction is a natural process that has been occurring since life began. As the earth changes in climate, disease, and food supply, some species can't adjust to changes and die off. New species take the places of the extinct ones. Over the earth's history extinction has occurred slowly. During the great dinosaur die-off, the rate of extinction was only one species every thousand years!

Why worry? If extinction is a natural process, why should we care about animals and plants disappearing?

In the last 300 years the human population has increased very quickly; consequently, the rates of extinction for other species have also increased. In fact, the extinction rate has increased more than 1,000 times since modern humans showed up.

Plants and animals do not suddenly become extinct. Instead, their numbers slowly decline. Scientists have names for the different stages that species go through as they head for extinction: rare, threatened, endangered, extirpated, and extinct.

Hack Box for Peregrine Falcon

Stages to Extinction

• Rare: Plants and animals are rare when there are few of the animal or plant in the wild. Some animals are naturally rare, while others are rare because their habitat has been destroyed or they have been killed off. The river otter is naturally rare, even in areas with good habitat, because it does not like to be around humans. The ginseng plant was once common, but now it is rare because people gather it to sell for medicine.
  
  
• Threatened: A species is considered threatened when its numbers are seriously declining. The loggerhead shrike is a threatened bird in the Lake States because its prairie and scrub habitats are disappearing. The gray wolf is also threatened in the Lake States.
  
  
• Endangered: A species that is headed for extinction is endangered. Endangered species are unusual wherever they are found. Their populations are often small and declining. The peregrine falcon and piping plover are two endangered birds in the Midwest.
  
  
• Extirpated: An extirpated animal or plant species no longer exists in part of its home. Many animals are extirpated from parts of their original homes. Wolverines and mountain lions once lived in the northern forests of the Lake States, but now can only be found in Canada.
  
  
• Extinct: A species that is extinct has no living individuals. Dinosaurs were once numerous on earth but became extinct before modern man lived. Humans drove the passenger pigeon and heath hen to extinction by over-hunting. When a species becomes extinct, there is no way to bring it back. Passenger pigeons are now only found mounted in museums like the Bell Museum at the University of Minnesota.

1. Protecting habitat. Habitat loss is the major cause of extinction. Parks and wildlife refuges around the world protect some habitats. However, the amount of land protected worldwide is still too small to help many endangered species.
   
   
2. Restoring habitat. Habitats that have been altered by pollution, deforestation, or agriculture sometimes can be restored. In fact, many lakes and rivers are now cleaner than they were 20 years ago. People have restored some prairies and wetlands as well. Still, preserving habitat when it's healthy is easier than restoring damaged habitat.
   
   
3. Laws. In the U.S. and other countries, we're passing laws to help protect endangered species. In 1973, an agreement called the Convention on International Trade in Endangered Species (CITES) treaty was signed by 86 countries. This treaty bans the trade of products made from endangered species. If selling and buying these products is illegal, the hope is that people will kill fewer animals. The United States Endangered Species Act, also passed in 1973, makes it illegal to kill or capture endangered or threatened species in the U.S. The law also protects some wildlife habitats.
   
   
4. Captive breeding. Another method of helping endangered species is to increase their numbers through captive breeding. Zoos and botanical gardens collect and raise rare animals and plants. Biologists try to get these species to breed in captivity. However, many wild animals and plants do not reproduce well in zoos and gardens. Although captive breeding can help, preserving habitat is the real key to saving endangered species.
   
   
5. Research. There is still a lot we do not know. Often we don't understand why a species is in trouble. Research can help us learn different ways to prevent extinctions.

Wild Fact Peregrine Falcon In the 1960s peregrine falcons were in trouble. They were being poisoned by the insecticide DDT and were almost extinct in the eastern U.S. DDT was banned in 1972 to protect peregrine falcons, bald eagles, and other birds. Soon birds were eating prey free of DDT. However, there was still a problem. There were too few peregrine falcons left in the wild, so biologists worked for years to raise peregrines in captivity. When the young falcons were ready, they were set free on skyscrapers mimicking the high cliffs where they use to nest. Now there are more than 200 peregrines in the eastern and midwestern U.S. Peregrines are still endangered, but at least now they have a fighting chance at survival.

Reintroduction of Peregrine Falcons in Minneapolis

Career Considerations

One important way to save endangered species is by breeding them in captivity. Some animals are easy to breed and raise in captivity, but others are much more difficult. Zoologists and zoo vets who do captive breeding have training in biology, ecology, genetics, and reproductive physiology.

Additional Activities

Research a plant or animal that is threatened or endangered in your area. Design a newspaper, radio, or television announcement to tell people about that species. Explain what can be done to save the species and why people should want to save it.

Know your products. You can help endangered species by learning about them and by thinking about how your actions affect wildlife and habitat. Consider the products you use every day. What natural products, or raw materials, are used to make them, and what habitats are affected when the products are made? Do they come from endangered species habitats?

Nest search: Search for birds' nests in your neighborhood. Nests are an indicator of bird populations since most pairs of birds in an area build nests. Do not disturb nesting birds or remove nests from trees, even if they seem to be abandoned. Tally the number of nests you find. Multiply the number by two (for two birds in a pair) to estimate the number of birds in the area.

Sample garbanzo bugs. It's best to try this in some natural area with grasses, bushes, trees, and other plants around. You'll need dried beans and a wire hanger. Make a frame with a hanger by bending it into a circular shape. Toss two handfuls of beans gently into the air (you don't want the beans to land too far apart). Now toss the frame onto the ground in the area where the beans landed. Count the beans that are found inside the frame and record the count. Toss the frame and count the beans a total of eight times. It doesn't matter if the frame lands near or on the same place more than once. Add all your counts together and divide by eight. This is the average number of garbanzo bugs that "live" in the area of the hanger. Estimate the number of hangers that could fit in the area and multiply this number by the average number of bugs in the hanger to get a total population estimate.

Fair Ideas

Follow an animal population and graph its change from year to year. Get information from the Department of Natural Resources (DNR). Explain why it is changing.

Species Display: Make a display showing the life cycle and habitat needs of an endangered or threatened species. Illustrate how the activities of humans affect the species. Include information about the reasons the species is in trouble and what is being done to try to save it.

Minnesota State Fair

Endangered Species Book: Make a book describing 10 threatened or endangered species. List information about each species such as its habitat needs and why it is threatened or endangered. Include a drawing or picture of the animal. You may want to have themes such as Minnesota Endangered Species, Endangered Birds, or Endangered Prairie Species.

Personal Web of Life: Make a mobile or three-sided display that illustrates at least five components of your own web of life the different animal and plant products that you often use. Describe what animals or plant each comes from and how your use of the resource might affect the world. Include drawings, photographs, or examples of the resources in the web. You might also want to include a map of North America or the world to illustrate where the products come from.

Tips for Making a Three-Sided Display: It's a good idea to get your leader, parent, or other adult to help you. Use a material such as hardboard, particleboard, or plywood. Poster board is not as sturdy. Open displayed dimensions should not exceed 12 inches deep by 18 inches wide by 22 inches high. Use hinges to attach the sections to each other. Paint or cover the background with adhesive paper, if you'd like.

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