Modeling the Effects of Habitat Fragmentation

Transcription

1 UNIT 5 CHALLENGE LAB Modeling the Effects of Habitat Fragmentation Background Large and continuous tracts of land were once found in abundance on Earth. Unfortunately, in many areas only patches are left. This is because the habitats have been and are being fragmented, or broken into smaller areas. Habitat fragmentation can result from natural processes such as fire or landslides, or from human processes, such as cutting forests down for fuel and lumber. When habitats become fragmented, the remaining patches of habitat are often far from each other, which isolates individuals and leads to loss of genetic diversity in a population. Fragmentation can alter temperature, wind, amount of sunlight, and water availability in a habitat. It also changes habitat boundaries (edges) and predatorprey interactions. Living things depend on each other; the loss of one species because of fragmentation can cause great harm to other members of the food chain. MATERIALS 8 11 grids calculator black pen blue pencil red pencil PROCESS SKILLS Calculating Inferring Analyzing Modeling Scenario You have been hired as a member of a Habitat Fragmentation task force for the U.S. Fish & Wildlife Service. In recent years, urban development has adversely affected habitats, and a proposed shopping center in a nearby forest area will likely do the same. Your job is to model the effects of habitat fragmentation on four different animal species (invented for the exercise). You will determine how the populations of these animals are altered by a change in their living environment. Problem How does habitat fragmentation affect a population of organisms? Procedure Part 1 A natural forest 1 Obtain an 8 11 grid from your teacher. This grid will represent an unfragmented forest. Each group of 4 squares represents 4 square miles. How many miles are represented by each individual edge of a box? What is the total area of this forest, in square miles (mi 2 )? ECOLOGY 67

2 How many miles is the forest edge? (Hint: Two of the sides of the forest are 22 miles long.) Check your answers with your teacher before proceeding. 2 Next, you will determine the individual habitats of four of the animal species in this forest. Read the descriptions of these species in Table 1. For each, place its corresponding letter into every box in which it might nest or have a den (use a pencil or black pen). For example, species A sleeps up to 2 miles into the forest. So you would write an A in each of the boxes lining the outside of the grid. TABLE 1. DESCRIPTIONS OF SPECIES LIVING IN THE FOREST Species Description: Number per 4 square miles Species A This mammal is a predator that lives at the edge of the forest (sleeping up to 2 miles in). It will occasionally travel an additional 2 miles into the forest to prey on bird eggs. It will climb 15 feet up a tree to find bird eggs in a nest. 0.5 individuals (or 1 individual per 8 square miles) Species B This mammal is also a predator; it lives inside the forest. It prefers to live at least 4 miles away from species A s sleeping area, and doesn t venture out of its own nesting area for hunting. It preys on bird eggs and small animals. Species B will climb 30 feet up into trees. Species C This bird lives in trees in the forest, at least 4 miles away from the forest edge. It builds its nest 25 to 35 feet up in tall trees. Species D This bird lives in trees in the forest, at least 2 miles away from the forest edge. It builds its nest 10 to 15 feet up in tall trees. 1 individual 2 pairs 1 pair ECOLOGY 68

3 3 Calculate the total area in which each species can sleep (nest), and write it below: Species A: Species B: Species C: Species D: Check your answers with your teacher before proceeding. 4 Look at the information about the average number of individuals of each species found for every four square miles in Table 1. Determine the number of individuals of species A and species B in the forest. Then calculate the number of pairs of species C and species D in the forest. Number of individuals of Species A: Number of individuals of Species B: Number of pairs of Species C: Number of pairs of Species D: 5 Predator-prey interactions. Using the information from Table 1, answer the following questions: Which species (C and/or D) will species A prey upon (that is, which bird s eggs will it eat)? Which species (C and/or D) will species B prey upon (which bird s eggs will it eat)? Next, take a blue pencil and make a checkmark in each box that species A hunts bird eggs in. Using a red pencil, do the same thing for species B. Keep in mind how far each of the predators stays away from the other and how close to their sleeping areas they hunt. ECOLOGY 69

4 Part 2 Fragmenting the forest 6 Now choose another blank 8 11 grid. This again represents the forest habitat (each box in the grid is still 4 square miles). However, imagine that a large shopping center has been built in the forest. It takes up 8 square miles. Mark large X s through the squares on the grid that represent this area you can choose its location. If you put the shopping center in the middle of the forest, you should also mark a path (X out squares on the grid) for access roads to be built. Assume a road will take up an entire square. Show your grid to your teacher before proceeding. Now what is the total area of the forest, in square miles (mi 2 )? How many square miles of forest were lost because of the shopping center? How many miles of forest edge space are there in the forest with the shopping center? Is the number of miles more or less than it was before? 7 Now determine the possible nesting/den areas of each of the four animal species in this newly transformed forest. For each species place its corresponding letter into each box, like you did in step 2 for the other grid. (Use the same information.) 8 Calculate the new total area available for each species to nest in, and write it below. Also specify if this is more or less space than in the forest without the shopping center. Species A: Species B: Species C: Species D: 9 Using the information in Table 1, determine the numbers of individuals of species A and species B and pairs of species C and species D in this altered forest (as you did before in step 4) and write them below. Number of individuals of Species A: Number of individuals of Species B: Number of pairs of Species C: Number of pairs of Species D: ECOLOGY 70

5 ) Take a blue pencil and make a checkmark in each box that species A hunts bird eggs in. Using a red pencil, do the same thing for species B. Are the hunting areas the same as they were in the forest without the shopping center? If not, how are they different? Analyze and Conclude 1. Analyze Explain the effects that building the shopping mall had on each of the forest species A, B, C, and D. How did the population numbers change? (That is, were there more or fewer individuals or pairs?) How were hunting areas altered? Was any species unchanged? 2. Analyze If the population of a prey species drops, what do you think will eventually happen to the population of predators? 3. Predict Imagine that the addition of the shopping center brought in raccoons that previously did not live in the forest. The raccoons raid the garbage cans at the shops but also will eat bird eggs. How might this affect the native forest species? 4. Predict What if the raccoons themselves became a food source for species A? How might this affect the forest species? 5. Predict Suppose that species A gets its water supply from a stream outside of the forest, and that the other species get their water from a pond inside the forest. How would removal of the pond affect each of the species? ECOLOGY 71

6 6. Calculate The shopping/business center and roads may be removed from the forest in an effort to return it to its natural state. New trees can be planted where they were cut down. If each of these new trees grew 2 feet a year, how many years would it be before species C nested in them? 7. Connect Building roads and shopping centers are two human activities that can cause habitat fragmentation. What are other examples of activities that may cause habitat fragmentation? (Hint: Think of ways we change the environment to produce food or find energy sources.) 8. Connect Computer models designed by scientists predict how habitat fragmentation will affect various species of plants or animals. How might a scientist determine if fragmentation has already harmed a species? ECOLOGY 72