High School Series • Ecosystem dynamics

Nov 17, 2016

In this series, we’ll follow Bethany, a sophomore biology teacher, as she leads her students through a unit on ecosystem dynamics. The ecosystem students are studying is located in the northern forests of Canada, where a population of hares mysteriously goes up and down every eleven years. This anchoring event is complex to explain and scientists do not even agree on the causes. Students begin with a number of hypotheses—some plausible and some “out there”—and these partial explanations change over time as they conduct investigations, read, and deliberate about an evidence-based account of this phenomenon. Near the end of the unit, Bethany asks her students to use their new understandings to predict what will happen in a different ecosystem (in Yellowstone National Park) as wolves are re-introduced to the area.
Opening interview with teacher
Our high school teacher, Bethany, describes her school and students. She frames her goals for instruction in terms of how she wants students to develop ideas over time, and learn to participate in science practices.

Planning for a high school unit
Bethany describes her planning. She is intentional and systematic. She uses the first set of core practices to modify her existing curriculum and design a sequence of learning experiences for her students. These experiences all build towards an understanding of a complex, puzzling anchoring event. This event is the cyclic population fluctuations of the snowshoe hare in the northern forests of Canada. Even scientists are not sure about all of what’s involved with this phenomenon—so it is an authentic question.

Eliciting students' initial ideas
Bethany begins by asking her students what might happen to a population of hares over time. Just that question was enough to activate students’ prior knowledge and to get them hypothesizing. Later, she shows her students only a small portion of the larger anchoring puzzle—why would a hare population go up, then down? Bethany has her students use a “partner talk” routine that gets students to really listen to one another when they are paired up. Its early in the school year, so she is explicit about her expectations and she is patient about clunky implementation by her students.

Eliciting ideas lesson continued
This lesson continues as students have been given just a bit of information about the snowshoe hare and its habitat. We find that students can’t hypothesize in these cases with zero background. It can appear they are unwilling to participate, but they just need a minimum of data to start reasoning with their peers. Bethany has her students develop initial hypotheses on large poster paper. She then makes all these public, so that students can see the reasoning of their classmates. You’ll also see the talk norms that students use in whole class talk. There is a segment where a student helps an ELL peer to contribute to the small group discussion and this peer later adds sophisticated ideas to the group conversation.

Comparing hypotheses across groups
Here the teacher has her students think about the kinds of evidence that might be collected to support or refute their hypotheses. Bethany has students share hypotheses between groups and prompts everyone to make sense, even if they don’t agree, of another group’s mini-theories.

Near the end of class, Bethany has students in whole group help her fill in a chart about what features the different hypotheses had in common, which seemed unique, and which ones were the strongest.

Creating initial models
The teacher has her students construct with her a set of criteria that make for a strong hypothesis or explanation. The criteria include 1) likelihood, 2) fits with all data patterns, and 3) based on known science. She then has an explicit conversation with students about the nature of evidence. Later in the lesson she has another explicit conversation with students, this time about what makes a good model. Students then are given cut-outs of various parts of this ecosystem and are asked to link them in ways that can help explain the up-down fluctuations of the hare population. These models, will of course be revised as new ideas and evidence come to light. This is what modeling, as a science practice, is all about.

Supporting ongoing changes in student thinking
Here Bethany introduces the ideas of carrying capacity and limiting factors. Then she has them engage in a data collection activity that compels students to make sense of these ideas (rather than using the activity to confirm the ideas). Midway through the lesson is an example of how the everyday cultural knowledge of one student helps him understand complex ecological ideas. Even he is surprised by how much he knows, when prompted to talk more about invasive species on an South Pacific island that his family comes from. Bethany uses his knowledge the next day, adapting her lesson to take advantage of his experiences. We also see examples of students having their thinking about carrying capacity changed by listening to members of their group and other small groups. Bethany ensures that these opportunities are always there for her students.

Thinking about human populations
Bethany asks students to think about the world population of humans, and what our carrying capacity might be. This sparks another round of sense-making talk. She then gets students to talk about their classmate’s experiences voiced on the previous day regarding invasive species on his home island. Near the end of class, Bethany has her students start a Summary Table (she calls it a chart). Bethany has interesting and productive variations of the columns on this table.

Revising hypotheses
The teacher now has her students put up their group hypotheses on the classroom walls and start grouping them. Some students start to say that by the end of their unit, their final explanations should probably have elements of many of these different hypotheses. This is great insight about how science works—robust explanations of complex phenomena integrate multiple ideas together.

Revising models
Here Bethany asks her students to revise their initial models, based on new knowledge and evidence. She uses a great scaffolding tool for this, and structures the kinds of revising that students can do. “Structuring” as we use the term means helping them understand what’s possible—it does not mean constraining them. This episode has many examples of how Bethany circulates around the room, visiting tables, listening intensively, and then offering probing questions to get students to think more deeply about what they yare changing and why.

Compilation of lessons supporting on-going changes in student thinking
This is compilation of different lessons in which Bethany uses the core practices of “Supporting on-going changes in student thinking.” She has students do mini models of how energy is transferred in ecosystems. She has students do an activity in which energy is passed upwards through trophic levels. Students collect data on this phenomenon. What the beans represent is not always clear to students, especially the ones that do not get passed along. Even graduate students in college get confused by this! In another lesson on this video Bethany introduces the idea of nutrition at the molecular level, which leads into discussions about the carbon and nitrogen cycles in an ecosystem.

Students read science journal articles
This video surprised us. Bethany gave summaries of actual science journal articles to her students. These summaries contained the original data representations (graphs of various types). She asked her students to read these in groups (scaffolded this process of course), and present to the whole class what they felt the main points where that had relevance for the hare phenomenon. Students were amazing at decoding the science talk and making sense of the data as well as the science arguments. This is a great way of exposing students to arguments by scientists. One of the most intriguing findings was that plants, if over-grazed by the hares, can actually start producing new vegetation that inhibits hare reproduction.

What happens at the end of the unit
This video shows Bethany doing a number of sophisticated moves near the end of the unit. She has students develop with her an explanation checklist. This is a list of all the ideas that students feel should be included in a credible and complete explanation for the hare phenomenon. Again, students voice the idea that the best explanations will integrate ideas that were found separately on several different hypotheses drafted at the beginning of the unit. Following this, students re-construct their final explanations, using all resources at their disposal, like their notebooks, the Summary Table, and other artifacts around the room. On the final two days of the unit, Bethany takes the modeling a level higher. She asks students to use what they know, and apply it to another ecosystem. Students are required to model and explain what is likely to happen with the re-introduction of wolves into that ecosystem. She requires that students use the very same explanation checklist that they developed for the hare phenomenon—perhaps students could then see that powerful ideas in science are powerful because they can help you explain a range of similar events.

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