Earthworm Invasion (Part 1/2)
Lesson 4 of 12
Objective: Students will investigate a real-world example of interspecific competition.
Today students will explore a study about the effects of invasive earthworms on a forest ecosystem. Earthworms are out-competing of a native millipede, but the millipedes are also putting selective pressure on the earthworm. This real-world case study then leads to a discussion of the problem that invasive species can have on local ecosystems. This is the first day in a two day lesson. Here is an overview of what students will learn today.
Play the song "Red Wigglers, the Cadillac of Worms" as students enter the class.
As the song ends, poll the class by asking
- How many of them fish?
- How many of them purchase bait from the local bait shop?
- What type of bait to they typically purchase?
(Note: As I am polling the class, I reveal that my favorite type of bait is night crawlers. Sometimes I even bring some newly purchased night crawlers to use as an example. I point out that I always seem to have more night crawlers than I truly need.Ask students "how many others have the same problem?" I wait for responses. I reveal that my biggest dilemma is what to do with the extra worms. I ask if anyone else has this problem and what do they do with the "extra" worms? I wait for student responses.)
Have students write their responses in their lab notebooks.
Using the Frayer method, define interspecific competition.
Understanding the Problem
Show students this BBC current event that discusses the findings of Dr. Bruce Snyder and his colleagues.
(Note: I follow with a screen shot of Soil Biology and Biochemistry journal article to which the BBC current event is referencing.)
In their lab notebooks, have students complete an outline of the article using the current events summary sheet which asks students consider who did the research, what was researched, how was the research performed, when was the research performed, how was the research performed, and why is this research important to science. The first five questions are required factual answers that are gleaned from the article, while the last question is based on the reader's opinion.
Have students popcorn read the abstract aloud. Students should highlight any unfamiliar words in yellow. They should also underline the statement they think is the hypothesis of the study.
After students have read the abstract, discuss as a class any unfamiliar vocabulary particularly the terms holotype, genus, and species.
Ask students what they think the hypothesis of this study is. Then have students rewrite the study's hypothesis in their own words.
Pair the students into groups of two (typically with their shoulder buddy) and have them determine the experimental groups. Students should sketch them as an image or organize them as a graphic organizer or chart on their student handout.
After several minutes, come back together as a class. Have several students share their graphic organizer to ensure that everyone has a good understanding of the experimental design.
With their shoulder buddy, students should analyze data concerning the following:
- millipede mortality
- earthworm mortality
- mean fresh weight change of surviving fauna for millipedes and earthworms
Then, students should summarize the trend of the two graphs.
Next, students should determine the mean fresh weight change of surviving fauna for millipedes and earthworms by using the raw data on the student handout.
- Using Vernier's Logger Pro, students will graph the averages of the raw data.
- One person in the group should calculate the averages and the other one should record the data in Logger Pro.
- Once all three treatments are graphed, students should predict the line of best fit using the "draw prediction" feature under the analyze tab of the program.
- Finally, students use Logger Pro's analysis software to determine the line of best fit (select Analyze, then select Curve Fit, then Try Fit, then OK).
- Students should annotate the graph with a trend of the graph.
Bring the class back together and ask students what they determined concerning millipede and earthworm mortality. (Note: I aid my students by projecting the graphs and having the students follow using their handouts.)
Next, ask what they can tell me about the graph they just created using the raw data. Wait for student responses.
Have students summarize the key findings so far in their lab notebooks. Ask the students to circle the area in the graph that shows certain key findings of the study as summarized by Dr. Snyder's abstract.
Finally, as a class Look at the earthworm fecundity data. Explain why it is important to measure the earthworm's reproduction rate and why the dip in the rate of reproduction along with the decrease in mass shows an indication of interspecific competition.
After discussing fecundity, have students summarize three of the study's key findings on their handouts. Then, have several volunteers share their findings. As needed, add or clarify the findings from Dr. Snyder's team.
Next, show them images from the damaged ecosystem and discuss how the small changes in the leaf litter cause other changes throughout the area.
Finally, show students the Earthworms Across Kansas page. Lead students to the distribution maps. Pick two species (one native and one invasive species). Have students hypothesize how they think the non-native worm got to that area of the state. Also have students hypothesize how they think these non-native earthworms might change the environment in which they are now living. Have students record their findings in their lab notebooks.
HOMEWORK: As the evening's homework, they are to explore the distribution of both worms. Students should choose two additional species (one native and one invasive species). They should pay particular attention to the non-native worms.
They should consider the following:
- Hypothesize how they think the non-native worm got to that area of the state.
- Hypothesize how they think these non-native earthworms might change the environment in which they are now living.
- Record their findings in their lab notebooks.
Students will report their findings during the next class period.