Disaster? Community Disturbances and Stability

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Objective

Students will be able to describe specific types of disturbances that affect ecosystems as well as distinguish between the processes of primary and secondary succession.

Big Idea

Following significant disturbances (such as natural disasters or human activity), ecosystems often follow predictable patterns of succession to restore stability.

Introduction

This lesson covers ecological disturbances (such as natural disasters and human activity) and how ecosystems can eventually stabilize through the processes of primary and secondary succession.

 

The lesson essentially consists of two parts:

1. A pre-class textbook reading and homework assignment focused on close reading techniques, critical-thinking questions, and content vocabulary development.

2. An in class presentation that provides supplementary examples to review the concepts and vocabulary from the chapter along with a class discussion seeking to draw students into more critical examination of the topic at hand and assist in their ability to connect the concepts to their personal experiences. 

The textbook reading comes from Environmental Science: Your World, Your Turn by Jay Withgott.

If you do not have that particular textbook, I would recommend finding a similar chapter or chapters and modifying the lesson accordingly.  

Alternately, the powerpoint attached to the Direct Instruction section covers most of the same concepts and vocabulary as the chapter.  If you have a shorter class period, you may want to skip the reading assignment and assign the discussion questions as homework.  You could then hold the class discussion on the following day.       

In my case, I assign the textbook reading on the meeting previous to this lesson.  In that way, students will have already covered the concepts on their own and the powerpoint presentation will be less of a lecture and more of an opportunity for students to ask questions and clarify their understanding. 

Connection to Standard:

In this lesson, students will prepare for class by reading and determining the central idea of a text, establish familiarity with relevant scientific vocabulary, and then draw evidence from the text to support arguments and opinions presented as part of their participation in a group discussion.  

 

Direct Instruction

30 minutes

Like I mentioned above, I assign the textbook reading as a homework assignment to be completed upon arrival to this class period.  The powerpoint presentation is then more of a review and an opportunity for students to ask questions.  

 

Wondering WHY I use lectures as a pedagogical strategy?  Watch this video.

Wondering HOW I use the Powerpoint to differentiate instruction? Watch this video.

Wondering why I choose to have a reading assignment AND a lecture on the same content?  Read this rationale.

Wondering how you might use this lesson's resources if you don't plan on presenting a lecture? Read this reflection.

 

When class begins, I ask students to get their homework out and first give them about 10 minutes to discuss the critical thinking questions with their group members.  During this time, I walk around and put a stamp on completed homework and answer any questions that students bring up.  If students bring up a good question or insightful comment, I ask them to please remember to bring that up in the larger class discussion to follow the presentation.  

Affording this time before the presentation allows students to "field test" their answers with a smaller group, increasing their confidence to participate in the larger discussion.  Also, because the discussion is graded by groups, it allows the ideas of individual members to influence the thinking of their peers which may lead to greater insights or even new questions.  Finally, while I walk around, I listen to the nature of student discussions and get a better sense of what kinds of questions may be floating around the room, allowing me to emphasize certain aspects of the lesson or offer more detailed examples to scaffold the instruction.

After I have stamped all the homework assignments, I distribute the note sheet that accompanies the presentation.  As I've mentioned in previous lessons, offering students a note sheet provides a readymade study guide for later and allows students to focus on their thoughts and the concepts being discussed as opposed to focusing all of their attention on copying down copies amounts of notes.   

 

Please Note: Although I routinely check for understanding throughout the presentation, I find it important to really do thorough checks for understanding on a few points:

  1. The question of "Are Humans a Keystone Species?" really provides some good material for a discussion.  On the one hand, we go into so much detail about how we negatively affect ecosystems.  On the other hand, like beavers, our constructions and habitat alterations end up providing resources and habitats for different kinds of organisms and end up sustaining different ecological communities than would otherwise exist without our presence.  So this question is really a matter of perspective.  To a large predator like a tiger, humans are pretty terrible because we fragment their large range into unsuitably small islands of forest.  To a rat or a pigeon, we're pretty good at sustaining the kind of habitat that they excel in.  
  2. The contrast between primary and secondary succession is explored in detail in the discussion guide for this lesson.  However, I find it important during the lecture to explain that although all communities go through succession, a climax community will be unique to a particular biome, depending on the environmental conditions there.  This is an important point to make because some students may get the misconception that a desert or chaparral, with their relatively shrubby, short plants might be "stuck" in an early stage of succession, when in fact, they represent the climax community of that particular region.  This concept is covered in much more detail later in the biomes unit when we discuss the relationship between biomes and climate.

 

Discussion

30 minutes

Following the presentation, I let students know that we will wrap up by having a class discussion to review the concepts of the lesson.  Again, depending on your class length, it may be preferable to have this follow-up discussion on the following day.  

The discussion protocol for this lesson:

  1. all groups are required to participate in the discussion and will receive a “participation” grade for the day

  2. groups with more than one member that participate will receive a higher participation grade

  3. groups that participate more frequently will receive a higher grade

These criteria make the group collectively responsible for their grade and accountable to each other. If no one in the group participates, the group as a whole will receive a failing grade.  If only one member of the group participates, regardless of how often, the group can’t receive any grade higher than a C.  

 

To keep track of participation, I begin by making a map of the class with the group tables labeled by group name.  Since there are four students at each table, as a student from a particular group participates, I make a tally mark in the position of that student in their group.  In this way, I can tally how often the group participates, which members are participating, and how often.  To determine "average" participation, I add up all tally marks and divide by the number of groups, rounding down.  I then use this rubric to determine their participation grades.

 

See this discussion guide for specific strategies for this discussion, but I would bring your attention to two key points from the guide that may guide how you lead the discussion:

1. On the question of what makes an exotic species an invasive species, it's important to clarify that an exotic species is any non-native species.  However, an exotic species isn’t considered invasive until its population grows so rapidly that it negatively impacts the native communities.  So I would make sure that students understand that although all invasive species are exotic, not all exotic species would be considered invasive.  This distinction will become especially important later in the year when my students complete a biodiversity survey and can see, firsthand, that many of the species in their local ecosystem are exotic, but the majority of these non-native species are not negatively impacting the community.

2. As for the extra credit question, I assign this question as extra credit because I really hope to get students thinking about what a city may look like after humans.  This could make a good separate project if you want to devote the time to it.  I would actually do that in conjunction with the “Who are the Creatures in Your Neighborhood” project because that would provide a good baseline of the species already present to better understand how they may be affected by the absence of humans.  This question allows students to integrate a lot of their ecological knowledge from previous lessons.  In addition to questions of primary and secondary succession, students can consider which species depend on the human-influenced urban ecosystem and which species would be more likely to thrive in an environment devoid of such human influence. 

One neat idea could be to show students articles from a travel magazine and have them write an article for a "travel magazine of the future", complete with pictures and detailed descriptions of the community thriving in an abandoned city.