Population ecology

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Students will be able to: 1) Define the factors that regulate the size of a population; 2) use appropriate terms to describe examples of population ecology case studies; and 3) develop an original example of population ecology key terms.

Big Idea

Population ecologists study the factors that regulate population abundance and distribution. How might we develop a working knowledge of the central ideas of population ecology in order to assess the characteristics of a population?

UNIT FRAME: Populations

How might we manage the human population? Understanding the factors that promote and constrain population growth is essential for the development of solutions to problems caused by growing populations. How does a population obtain its food? In what climates will a population thrive? Once we understand what a population needs, we can influence population growth by manipulating those needs.

Unfortunately, the human population is a special case. Unlike other species, humans are often able to overcome natural limits to population growth, especially because of technology. Humans are able to live nearly anywhere; humans grow food; humans have developed defenses against deadly disease. Humans overcome the usual barriers. This overcoming entails strong negative impacts to our planet. We are members of a species that continues to overshoot a natural carrying capacity, seemingly without consequence. We grow exponentially on a planet where logistic growth is the norm. And in so doing, we stress the spectrum of biotic and abiotic factors. 

Such stress is evident in the human impact on the environment. Already climate change models suggest that many of the extreme weather events over the last decade have an origin in human population growth. Along with biodiversity reduction and ecosystem destruction, the human population does not have a strong track record.  And as the human population continues to grow, it will continue to negatively affect the environment.  What might be done?  

This unit approaches human population growth from an engineering design perspective. How might we begin to manage our species? To develop management strategies, students will lean on population growth models, carrying capacity and reproductive strategies models, historical data of human population growth, the demographic transition theory, and the IPAT human influence model. Students will engage in modeling, mathematical thinking, reading of complex text, debate, public presentation, and engineering design thinking process. 

Throughout this unit the pedagogical approach is constructivist as much as possible. Students will work with teacher-curated resources to make meaning. These include raw data, primary sources, case studies, and problem-based activities. As with the other units in this curriculum, the goal with this approach is to draw on students' existing knowledge, skills, worldviews, and lived experiences to craft learning experiences that allow for students to master learning objectives in a self-directed manner. The teacher is the "guide on the side, not the sage on the stage." To this end, the unit continues to ramp up a model of blended learning that allows for students within the same cohort to take personalized pathways towards mastery of common learning objectives.

The unit CAPSTONE provides a snapshot of the major objectives for this unit. Student have an opportunity to develop rigorous solutions to problems created by a human population on its way towards 9 billion. In so doing, students will research, make meaning, publicly present, give and receive feedback, and iterate ideas.


LESSON FRAME: Why does population ecology matter?

How and why will the number of individuals within a species change over time? Humans are a unique species, but not so unique that we entirely escape ecological constraints. Understanding models of population ecology allow us to understand how we are different from other species, but also how we are similar.

Students must understand the vocabulary and basic concepts of populations to communicate effectively about them. This lesson is primarily an introduction to vocabulary and population dynamics. Students will learn key words and phrases through a variety of activities, use this vocabulary to describe a real-world example of population ecology, and develop original examples of each idea.  By the end of this lesson, successful students will have defined population vocabulary, used this vocabulary to describe a case study, and developed an original example for each term.

RESOURCE NOTE: The attached PROTOTYPE ACTIVITY GUIDE contains learning activities that might be modified by educators for classroom use.

FLIPPED: The history of life on Earth

What will students have complete before class?

Students have a FLIPPED assignment to complete before class--a quick tour of the history of life on Earth.  Using the service videonot.es, students take notes from a Crash Course Ecology episode.  This video is ~13 minutes and consists of concepts that students should have mastered during a 9th grade Living Environment course.

There are three tasks for this assignment:

  1. develop a content summary every two minutes
  2. write a final short paragraph summary of the main ideas
  3. to develop one question about content that was confusing.  

This question is used primarily by the teacher as formative assessment data.  What do students already know?  

ENGAGE: Paraphrase and "best guess" definitions

10 minutes

What is the purpose of this activity?

Students paraphrase the frame for the lesson and make preliminary meaning of population ecology vocabulary. By the end of this section student should have a "best guess" definition of six population ecology concepts.

What will students do?

First, students paraphrase the big idea.

Second, students develop a "best guess" definition for six population ecology concepts that will be the focus of the lesson.  The hint they are given is that many of these concepts were in the FLIPPED assignment, although not necessarily by name. This will be done as a silent writing activity. The terms are:

  • population ecology
  • population size
  • population density
  • population distribution
  • population sex ratio
  • population age structure

Finally, students consult the members of their table group to develop a shared "best guess" definition for each term and the team share out ONE "best guess" defined term to share with the class. This presentation should include a description of one aspect of the FLIPPED video that the group thinks illustrates the term.

What will teachers do?

Students will almost reflexively reach for a dictionary or search engine for this activity. Do not let students do this! By committing to ideas without the "answer" students are forced to potential make a public mistake. This will create some stress and possibly emotional anxiety. This is to be expected and supported. Students will learn these concepts more efficiently if they make meaning out of ambiguity, rather than starting with a definition. This "slow build" approach makes this vocabulary much more sticky.

EXPLORE: Pictures + terms

12 minutes

What is the purpose of this activity?

Students work in groups to build on their "best guess" definitions by attempting to match a term to a diagram illustrating the underlying concept. By the end of this activity student groups will have develop best guess definitions through collaboration.

How is the room designed for this activity?

Pictures representing each core concept are taped to walls at evenly spaced intervals.  Next to each picture is a chart paper for definitions that student will write. See the RESOURCES section for a few videos of room setup and student group process.

What will students do?

Student receive cards with the key terms from the opening engage activity.  The tasks for each group are:

  1. tape one word next to each picture using the "best guess" definitions as a guide;
  2. create a definition for each picture;
  3. use the plus and delta system to peer review at least THREE other student group definitions in the class.

Students are encouraged to collaborate with members of their group and with other groups. There is only one rule: each student in the class must be able to explain the choices made by his/her group using evidence.

What will teachers do?

Teachers should first model the procedure for this activity. Then teachers will primarly want to monitor the nature of feedback given during the plus and delta protocol. Feedback should take the form of "claim with evidence." Teachers will also want to be especially supportive of students learning English. This activity allows students that may not be able to read long text to access conceptual understanding of vocabulary through visuals. Teachers need to be especially vigilant about supporting these students.

How will we debrief this activity?

Once all cards have been sorted by all groups, we will have a whole group discussion.  I will facilitate this discussion by asking students at random to explain choices made in the sorting phase.  I will be especially vigilant with disagreements among groups.  What evidence did each of the groups use to place "population distribution" next to these three different diagrams?

EXPLAIN: Paraphrasing and norming definitions

10 minutes

What is the purpose of this section?

Students formally norm understanding of each term through teacher-facilitated discussion. By the end of this activity, all students should have a definition and diagram of each of the six terms introduced in the ENGAGE section.

What will the students and teachers do?

In lieu of a student-centered discussion protocol, this activity uses a more teacher-centered approach.  First, students will together read a copy of a short description of population ecology from Nature.  Students will then be given two minutes to paraphrase a definition of "population ecology." Students will share ideas through random cold calling

Finally, the teacher will "reveal" the correct pairing for the EXPLORE activity and explicitly provide a definition.  

  • Population size (N) is the total number of individuals within a defined area at a given time (California condor example)
  • Population density is the number of individuals per unit area.  This value can tell us if a species is rare or abundant or if a population might outstrip its food supply. (This is especially important for wildlife managers and wildlife zones).
  • Population distribution is a description of how individuals are distributed with respect to one another. (This may be random, uniform, or clumped.)
  • Population sex ratio is the ratio of males to females (usually 50:50 for sexually reproducing species).  This measure can be helpful in estimating the number of offspring a population will produce.
  • Population age structure is a description of how many individuals fit into particular age categories.  This measures help ecologists determine how quickly a population will grow.

Students will drag and drop diagrams into a table in individual documents. A sample of what student work will look like is in the RESOURCES section.

ELABORATE: Easter Island and Oak trees

20 minutes

What is the purpose of this section?

Students describe two case studies of population ecology using at least four terms. By the end of this section students should have used four vocabulary terms appropriately in a short written paragraph describing a population ecology case study. 

What will students do?

Students receive the options of pursuing one of two ELABORATE pathways:

  1. Easter island
  2. Oak trees' acorns

Each pathways is a story of population ecology that incorporates most of the terms introduced, but does not necessarily use the term.  Each student is challenged to paraphrase each story using at least FOUR of the terms introduced during the lesson.

What will teachers do?

The primary teacher move here is to monitor successful use of terms. I like to find models of excellent use and then pair struggling students with successful students. These models should be a single sentence, not an entire paragraph, and pairings should only be made for specific terms. The goal is to offer a struggling student a model, not a private tutor.

The RESOURCES section contains some representative raw data from students. In this lesson nearly all students developed proficiency with appropriate usage of terms. The next step will be supporting students' understanding of how these terms impact each other.

EVALUATE and EXIT: Examples

3 minutes

Student capture examples of THREE of the terms learned during this lesson on slips of paper to be handed in to the teacher.  Examples can take the form of written descriptions, pictures, or diagrams. They may be original ideas or sourced from online resources.  

How will the teacher use this data?

These exit tickets will be used primarily as a check for understand in order to identify areas that will need to be revisited during future lessons.