Mystery Graph: Purple Loosestrife & Galerucella Beetle

Mystery graph: Purple loosestrife & Galerucella beetle

Author Sarah Morrisseau Gulf of Maine Research Institute Vital Signs Program

Question How do scientists use graphs to understand how species interact and change over time?

Overview Use this activity to kick off a Vital Signs investigation focused on purple loosestrife (Lythrum salicaria). Use your graphing skills to figure out and explain what happened during a 12-year scientific study in New Jersey to control the spread of invasive purple loosestrife. Students learn about a similar study happening at the Rachel Carson National Wildlife Refuge in Wells, Maine.

Science & Technology Standards (MLR) A3 Constancy and Change Students describe how patterns of change vary in physical, biological, and technological systems.

B1 Skills and Traits of Scientific Inquiry Students plan, conduct, analyze data from and communicate results of investigations. B1d. Use mathematics to gather, organize, and present data and structure convincing explanations. B1e. Use logic, critical reasoning and evidence to develop descriptions, explanations, predictions, and models.

E2 Ecosystems. Students examine how the characteristics of the physical, non-living environment, the types and behaviors of living organisms, and the flow of matter and energy affect organisms and the ecosystem of which they are part. E2b. Describe ways in which two types of organisms may interact including competition, and predator/prey.

Grade Level 7, 8

Setting Classroom

Materials Computer & projector NECN video: http://www.necn.com/Boston/SciTech/Beetles-used-to-fight-invasive-plant-/1216068621.html

Time Needed 30-40 minutes

Activity Procedure

NOTE: For best results, play Oh Deer! Invasive Species Style to introduce the concept of species interactions and population change over time, and the skill of visualizing data and telling stories using simple graphs.

1. Present to students the following “mystery graph” of real scientific data. Tell them that each line represents a different population of plant or animal. Mystery Graph: What do you think this graph is telling us about these 2 populations? 90 80 70 60 50 40 30 20 10 0 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

2. Challenge students to explain what happened over the 12-year study between the 2 populations. Ask them to tell the “graph story,” just like they did during the Oh Deer! Invasive Species Style game. They may find their Oh Deer! graph trends and stories useful as they try to make sense of similar trends in this one.

3. Give students enough time to think about, talk through, and maybe even write down what they think is happening over time between the 2 populations. The mysterious ramblings might go something like this:  Overall the blue population decreases from 1997-2008. Maybe it’s getting crowded out by another species, or eaten, or maybe its habitat is changing….  The red population increases pretty quickly from 1997-2002, and then it takes a really big crash in 2003. Maybe it ran out of food or got a disease or something….  The red and blue populations are pretty steady from 2004-2007  Then they both go way down from 2007-2008

4. Once students have been given a chance to look at and process the trends, give them more information about the graph using a video “hint.” Show the NECN video from the Rachel Carson National Wildlife Refuge in Wells Maine: Beetles used to fight invasive plant July 14, 2008 Amy Sinclair http://www.necn.com/Boston/SciTech/Beetles-used-to-fight-invasive-plant-/1216068621.html

5. Based on what they learned from the video about purple loosestrife and the Galerucella beetle, have students try to fill in the “mystery graph” with a title and legend:

 Which trend line do you think is purple loosestrife?  Which trend line to you think is the Galerucella beetle?

It should look something like this: 6. Have students tell the story (or improve the story they started in step 3) of how these 2 species have interacted and changed over time. Draw on the Oh Deer! experience and the NECN video.

The graph story may be written (1) in table form, (2) directly on the graph, or (3) using pictures depending on student choice or preferred learning style (examples are below):

(1) Example story in table form:

1998 At the start of the study, purple loosestrife covered 80 percent of the study area. The Galerucella beetle (predator) was introduced by scientists to try to control the purple loosestrife population.

1998- The purple loosestrife population decreased quickly because the Galerucella beetle was doing 2000 what it was introduced to do – eat its leaves. The Galerucella beetle had plenty of food to survive and reproduce, so its population increased.

2002 The Galerucella beetle population hit its peak! The purple loosestrife population continued to decline because of predation by a large and growing beetle population.

2003 The beetle population crashed because it didn’t have enough purple loosestrife to eat to support its growing population. Some other factor like weather might have caused or contributed to the crash too. It looks like the purple loosestrife population was able to maintain its 2002 cover as a result.

2004 The beetle population started to recover because there was enough food to support reproduction. The purple loosestrife started to decrease again as their beetle predator increased.

2005- Interaction between the populations seems to have reached a steady state. 2007 2008 Both the purple loosestrife and beetle populations decreased. Purple loosestrife is being eaten by the beetles, and the beetles are running out of their food source.

(2) Example story in the form of an annotated graph:

The purple loosestrife population decreased quickly because the Galerucella beetle was doing what it was introduced to do – eat its leaves.

The Galerucella beetle population hit its peak!

The Galerucella beetle had plenty of food to survive and reproduce, so its population increased.

The Galerucella beetle had plenty of food to survive and reprodu

(3) Example story in the form of drawings:

1998 At the start of the study, purple 2002 The Galerucella beetle population hit its peak! loosestrife covered 80 percent of the The purple loosestrife population continued to decline study area. The Galerucella beetle because of predation by a large and growing (predator) was introduced by scientists beetle population. to try to control the purple loosestrife population, but the population hadn’t started to grow yet.

7. Share and compare stories.

8. Prepare to go look for purple loosestrife in your community during your own Vital Signs investigation.