Populations in Balance

Where is the remote island of Guam?

 

 

Initiate a class discussion prior to beginning the activity.

Paraphrase:

Today we are going to examine an unusual problem plaguing the remote island of Guam, a U.S. territory. Does anyone know where it is?

Which ocean is it in?

What is the closest other piece of land to it?

The closest continent?

How do animals get to this island? How do they get there now? Thousands and millions of years ago?

Display map. Use the "-" button in the lower right to zoom out.

Isolated ecosystems (such as those found on remote islands) are especially vulnerable to major disturbances.

In this Science Scene, a dialogue to read aloud as a class, three friends are being driven home from school by one of the friend’s older cousins who is a navy pilot in Guam. He is asked about Guam and mentions that it’s an okay place to live except that there are a lot of snakes. He hands his cousin a newspaper article that explains how the U.S. Department of Agriculture poisoned dead mice in an attempt to kill the invasive brown tree snake—an environmental disturbance that is causing ecological problems on the island. They try to brainstorm ways to get rid of the snakes but realize that there could be unwanted consequences for all solutions.

Some teachers have several groups of students read at the same time. Other teachers select a few students to "perform" in front of the class.

You may want to read the entire passage out loud to the class once before assigning roles to students or dividing up into groups.

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The Script:

Snake Invaders: Learning About Guam’s Ecosystem

Setting: Elena, Rachel, and Miles are waiting outside to be picked up from school. Elena spots Rachel’s dad’s car, but doesn’t recognize the driver, Rob.

Elena: Where’s your dad? Who’s that driving his car?

Rachel: My dad can't pick us up today, so my cousin is driving.

Miles: What? Didn't your cousin just graduate eighth grade last year?

Rachel: No, my other cousin, Rob. He's a pilot in the navy and is visiting us while he’s on leave.

Elena: Was he in a war zone?

Rachel: You should ask him. Hi, Rob!

Rob: Hey, Rachel! Long time no see! Uncle Steve sent me over to pick you and your friends up. Hop in.

Rachel: Yeah, I know. He texted me. Thanks.

Elena, Rachel, and Miles get into the car.

Elena: I hope I’m not being rude by asking, but were you in Afghanistan?

Rob: Nope, I’m stationed in Guam.

Miles: Guam? Where’s Guam?

Rob: It's kind of near Hawaii.

Miles: Must be a nice place.

Rob: It's okay, but it's full of snakes.

Elena: No way! I hate snakes!

Rob: No kidding. Especially the brown tree snakes; they’re everywhere! They're in the trees, in the bushes… Heck, I even found one in my bed once.

Elena: Do not tell me that.

Rachel: Can't people just get rid of the snakes?

Rob: They're trying. A lot of people use snake traps or dogs but nothing seems to work. You're not going to believe this, but just before I came here the Navy had me fly a helicopter over the jungle, and folks were chucking dead mice stuffed with poison out of the helicopter. The idea was to kill the snakes by having them consume the dead mice.

Elena, Miles, and Rachel: WHAT?

Elena: Did that really work? Do snakes eat dead mice? I thought they just ate live ones.

Rob: I knew you’d be interested in that, Rachel. Check out the newspaper article I brought you. It’s there on the dash.

Rachel: (reading)

Government Drops Dead Poisoned Mice from Sky in Another Attempt to Kill Tree Snakes

The U.S. Department of Agriculture experimented with a new method to reduce the population of the invasive brown tree snake. They put Tylenol tablets into dead mice, attached the dead mice to long strips of paper, and dropped them out of helicopters into the jungle. Acetaminophen is a chemical used in Tylenol and other drugs. It’s safe for humans in normal doses but it is poisonous to snakes.

This environmental disturbance is due to snakes brought to Guam from the Solomon Islands by the military after World War II. Since then, the brown tree snake population has exploded. Government officials say Guam now has one of the densest populations of snakes in the world.

Miles: That's crazy!

Rob: Yeah. They cause huge problems. Sometimes the power goes out because a snake damages the wires. They prey on pets and livestock. Keep reading.

Miles: Give me that newspaper, Elena! (grabs it)

Miles: (reading)

The non-native brown tree snake eats reptiles, birds, and mammals. It is credited with driving many native bird species into extinction. Bird species such as the Sihek (Micronesian kingfisher), Chuguangguang (Guam flycatcher), Ko'ko (Guam rail), and chichirika (Rufous fantail) were all wiped out by the tree snakes. A few birds were captured before they went completely extinct. The Sihek and Ko'Ko are now being bred in captivity, with the hope that someday these species can be reintroduced to Guam once the island’s ecosystem begins its recovery.

Scientists have also reported a huge decline in the populations of local mammals and birds. And since trees rely on birds to spread their seeds, the trees are also affected, thus demonstrating the interdependence of species on the island.

Elena: I thought this was just disgusting at first, but it’s actually a serious problem isn’t it?

Rob: When I left Guam they had snake-sniffing dogs at the airport.

Elena: That's to prevent the snakes from going other places, right? That would be really bad!

Rob: I know that people in Hawaii are really worried about the tree snakes showing up there and wiping out the native wildlife.

Rachel: I don't get why snakes are such a problem. Aren't there some birds or animals that eat the snakes?

Rob: There's nothing on the island that eats snakes.

Elena: There aren't any predators? No wonder the snake population is so big!

Rachel: Wait, couldn't they just bring a predator from somewhere else to wipe out the snakes? Is there some sort of animal that preys on snakes?

Miles: Like a hawk? Couldn't they just bring those to Guam to eat the snakes?

Rob: There’s no native hawk species on Guam. Wouldn't bringing another non-native species cause even more problems?

Elena: Hawks might eat other things, too. I guess you can’t tell them to just eat snakes.

Miles: What about using a disease that affects snakes?

Rob: That sounds kind of sketchy.

Rachel: Maybe the people on Guam should just eat the snakes.

Miles and Elena: Eww!

Rob: It’s actually not bad.

Elena: I did NOT just hear that.

Comprehension Questions

1. Complete the following sentence to summarize the problems on Guam: The government is trying to kill the brown tree snake because _____________________________________________ .

2. The newspaper article mentions that the brown tree snake population has exploded. This means that the brown tree snake population has:

1. disappeared quickly
2. decreased
3. blown up
4. increased dramatically

3. The newspaper says that the brown tree snake "is credited with driving many native bird species into extinction." This means that the species:

1. no longer exist
2. are hiding
3. were driven to another place
4. are threatened

Assign students to one or more of the questions. Have students discuss with their partners and try to reach an agreement. This activity is another opportunity for students to practice using scientific language as they discuss the questions.

You may opt to assign single questions in the third section, rather than having all the students answer all the questions. Students can discuss with their partners and try to reach an agreement about their answers to the questions.

Tell the students to be ready to share what they talked about with the rest of the class.

Discussion Questions

• The article mentioned that Guam has "one of the densest populations of snakes in the world." Can you explain this in a different way?
• How might the government find out if dropping poisoned mice from helicopters is effective?
• Plants depend on bees for pollination, and bees depend on plants for food. This situation is an example of interdependence. What are some other examples?
• Do you think bringing a predator that preys on brown tree snakes to Guam is a good idea? Why or why not?

Assign students to one or more of the questions. Have students discuss with their partners and try to reach an agreement. This activity is another opportunity for students to practice using scientific language as they discuss the questions.

You may opt to assign single questions in the third section, rather than having all the students answer all the questions. Students can discuss with their partners and try to reach an agreement about their answers to the questions.

The writing prompt asks students to write a letter to an angry airline passenger who was inconvenienced by an inspection at the airport. Students write from the perspective of an airline employee whose job it is to answer such complaints in a polite but informative way so that customers understand the reason for such searches. Students should use their new scientific knowledge as they respond to the customer.

Suggest students use the focus words in their letter if possible.

• native
• population
• interdependence
• disturbance
• recovery
• consumer
• producer
• predator
• prey

 

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Writing

You are a customer service representative at Islandhopper Air. You just received this email from a customer who is complaining about missing his flight.

Dear Islandhopper Air,

I am irate! I made it to the Guam airport in just enough time to catch my flight to Hawaii. However, I was forced to comply with some stupid inspection rule. Airport officials wanted to see if I had fresh fruit in my luggage. I told them I didn’t, but they went ahead and looked through my stuff anyway. When I told them that I would miss my flight, they just shook their heads and kept searching through my stuff. They said that they were especially worried about insect eggs getting off the island. What nonsense! My flight left without me because of your ridiculous rules. I want my money back, and I’m never flying your crazy airline again!

Signed,

Hula in a Huff

 

Your boss has asked you to respond in a respectful way to help this customer understand the importance of these inspections to protect the populations on other islands. Wow! You have a tough job, teaching science to an angry customer. Best of luck to you!

Use the focus words; they can help you make a better argument.

native • population • interdependence • disturbance • recovery

consumer • producer • predator • prey