Preserving Biodiversity: Threats and Solutions
Lesson 2 of 9
Objective: Students will be able to explain the reasons that biodiversity is threatened by human activity as well as describe multiple ways that concerned individuals and organizations are taking steps to preserve biodiversity.
This lesson covers the various factors that threaten biodiversity and the different methods governments, scientists, and activists are using to protect biodiversity.
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. The concepts covered in this chapter that I would look for in a different text are...
- A discussion of extinction rates, including the background rate and mass extinctions
- Extirpation vs. extinction
- Endemic species
- The variety of threats to biodiversity, which E.O. Wilson dubs, "HIPPO":
- Habitat destruction
- Invasive species
- (human) Population growth
- The different approaches to preserving biodiversity, such as...
- The Endangered Species Act
- Captive breeding programs
- National parks
- Biodiversity "hotspots"
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.
I start by again writing the benefits of biodiversity we discussed in that lesson on the board:
- ecosystem function
- recreation and tourism
I then ask students to quickly review these benefits in their small groups. I then ask students to offer a description of the benefits in their own words (again, see the final discussion section of the previous lesson for the guidelines to this short review).
After we have reviewed the benefits, I ask students, "Why is it important to protect biodiversity?" The obvious answer that I hope students can supply is that if biodiversity is not protected, then we lose the benefits. I then explain that in this lesson we will be exploring some of the specific threats to biodiversity and the approaches being taken to protect against those threats to sustainably preserve the benefits of diversity. Following that short explanation, I have a student volunteer distribute the notesheet and we begin the presentation.
Following the quick warm up, I begin the powerpoint presentation for this lesson.
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.
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.
During the presentation, I make sure to continually solicit student involvement by asking for them to provide personal experiences that might relate to the content and encouraging them to ask questions when they arise.
Please Note: Although I do frequent checks for understanding during the presentation, I would call your attention to a few key points in this presentation:
- Slides 3, 4, and 5 discuss the normal, background rate of extinctions compared to a mass extinction. Slide 5 shows the rate of extinction increasing exponentially over the past 200 years. This is an excellent opportunity to review human population growth from the populations unit. I ask students to make recall that lesson and make a connection between the two trends. Their conclusion should be clear: as the human population grows exponentially, so do the number of extinctions.
- There are a few points where questions in italics (preceded by a #) appear on the slides. During these points I allow students to have a short discussion with their group. During this time I walk around listening to student conversations, identifying those groups that have arrived at a response I'm looking for, or that might have an interesting take I hadn't considered. After a few minutes with a question, I ask groups to share out their responses and if I had heard something interesting while walking around, I call on that specific group to share their perspective. In this presentation, the #questions come at the following points:
Slide 8: #Why do you think that some scientists argue that extirpation is just as bad as extinction?
Extinction is the death of all members of a species, such that no remaining individuals exist anywhere on Earth. Extirpation on the other hand is the death of all members of a species in a certain area, though some individuals of the species still exist in other places on Earth. It’s important that students understand that extirpation increases the risk of extinction, because it isolates remaining populations and decreases genetic diversity, negatively affecting the overall fitness of the species. Additionally, it could be argued that extirpation is as bad as extinction because any local benefits of a species' presence is lost.
Slide 23: #Consider the tragedy of the commons. At what point does fishing become unsustainable?
This is a callback to the tragedy of the commons activity from the beginning of the course. Hopefully with a quick review of the activity (which I achieve by reminding them, "remember when you were collecting the different types of candy?", somehow candy sticks in their mind) will allow students to explain that fishing becomes unsustainable when populations are depleted to numbers that can not reproduce enough individuals to replace those that have been fished.
Slide #28: #When forests in the US are protected because of the ESA, does that mean that US companies and consumers are using less wood? If not, where does this wood come from? What additional environmental costs result from this?
This question is addressed in the discussion guide in the question about the costs and benefits of the ESA. Hopefully students can explain that even when forests are protected in the U.S., it doesn't immediately translate to a lower demand for wood products (though students may recall from the economics and the environment lesson that the price may increase). Additionally, hopefully students understand that the environmental costs of logging don't disappear altogether, but are rather transferred from one place to another: if certain resources can not be obtained legally in the U.S., this may cause more environmental harm in countries without biodiversity protecting laws like the ESA.
Slide #30: #Why do you think many endemic species are found on islands?
Hopefully students can recall from the adaptation, selection, and evolution lesson that since islands are isolated from other areas, species there may have evolved there independently of relatives on mainland areas.
Like the previous lesson, so much of the discussion of the homework questions occurs during the presentation as I pause to ask students to consider some aspect of the presentation and then share out their perspectives.
This leaves the remaining questions from the homework assignment to be discussed as a review of the concepts from this presentation.
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:
all groups are required to participate in the discussion and will receive a “participation” grade for the day
groups with more than one member that participate will receive a higher participation grade
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.
If you'd prefer to not give a grade for participation in discussions, see this reflection where I discuss the conditions that arose that allowed me to not to grade for participation but still have meaningful discussions with broad participation.
See this discussion guide for specific strategies for all the discussions that take place during the lesson, but I would bring your attention to the following for this final review discussion:
For the question that asks students to briefly describe (in their own words) how the following factors can threaten biodiversity, I split the threats among the groups, and ask each group to describe two of the threats. I then have groups share out their own explanations with the whole class after a few minutes. I also ask students to come up with specific examples of these threats. I then write each threat on the board and write the student-phrased explanation of why it threatens biodiversity, as well as specific examples they came up with of the particular threat.
- Habitat Change and Loss When habitats are degraded or fragmented, they become incapable of supporting the same levels of biodiversity than when they are untrammeled. [e.g., habitat fragmentation of mountain lions has led to inbreeding and frequent encounters with humans, usually to the detriment of the mountain lions]
- Invasive Species Invasive species can out-compete native species and disrupt native ecosystems, potentially leading to the extinction of native species. [e.g., Burmese pythons populations are escalating rapidly in the Everglades, coming into conflict with the native apex predator, the American alligator]
- Pollution Harmful substances in the air, water, and soil can have serious health effects on humans and other organisms. [e.g., acid rain can kill trees, Mercury can poison fish, etc.]
- Overharvesting Too much hunting or fishing can deplete populations to levels from which they can not recover. [e.g., poaching of slow-reproducing rhinos for their horns has made them critically endangered]
- Climate Change Changing climates can alternately expand and diminish ranges of different organisms, disrupting the balance of existing ecosystems. [e.g., without the reliable freezes that tended to kill many reproducing females, growing populations of pine beetles are ravaging pine forests in the U.S. and Canada]
For the question that follows this, asking which threats are problems in California, it may be more relevant to ask this question about your home state, depending on the area in which you and your students live.
With sufficient time to research, I’m certain students could come up with examples to demonstrate that all of the above threates are problems in California. However, examples of overharvesting and invasive species may be hard to come by based on their own experience, which is what I’m hoping students are sharing from.
I’m hoping that my students can point to freeways, numerous commercial and residential construction projects, and the urban “concrete jungle” they live in as examples of habitat change and loss. Pollution is especially obvious for students in Los Angeles because of the near-constant smog at certain times of the year. My students also mentioned litter as a type of pollution they’ve observed. Climate change is a global phenomenon, but one thing my students all mentioned was the severe drought California is now experiencing. They understood that this may be a result of climate change that has disrupted regular weather patterns (which we examined in the Los Angeles Climatograph lesson).
Again, the idea is to solicit examples of these threats to biodiversity that the students have observed in their own lives. Depending on your area, students may be able to come up with examples of certain threats more easily than others.