BSCS Science Tracks:
Connecting Science & Literacy
Second edition, © 2006 by BSCS
Investigating Ecosystems
Unit Overview
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Module Overview
Introduction to Investigating
Ecosystems
A redwood forest is a natural community,
an assemblage of populations of plants,
animals, bacteria, and fungi that live in
an environment and interact with one
another, forming together a distinctive living
system with its own composition, structure,
environmental relations, development, and
function. A redwood forest or an oak forest,
a piece of prairie or a patch of desert—
each of these can be approached as a
community, a system of organisms living
together and linked together by their effects
on one another and their responses to the
environment they share.
—Robert A. Whittaker, 1975
Natural communities, both local and far
away, are the subject of the lessons in this
module about ecosystems. No matter what the
community is like where you and the students
live, there is a natural community in and
around the human-made components. We want
students to become familiar with their local
“system of organisms” that live together, affect
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Module Overview
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one another, and respond to the environment
they share. In addition, we hope that students
will become interested in the diversity of
ecosystems found within the United States and
around the world. An understanding of the life
of organisms around us is critical to sustaining
life on the planet.
An ecosystem can be defined as a community
and its environment, treated together as
a functional system of complementary
relationships, and the transfer and circulation
of energy and matter. In other words, an
ecosystem is a collection of living things
(community) and nonliving things (environment)
that interact one with another. Through those
interactions, energy from the Sun transfers
through the system from plants to animals and
decomposers, and nonliving materials (matter)
are recycled through food webs.
The concept of an ecosystem is rather
new in science. The scientist A. G. Tansley
coined the term in 1935 because he reasoned
that understanding the whole system was
fundamental to understanding the behavior and
survival of individual organisms; one could not
separate the organisms from one another or
from their environment. A few years before that,
Charles Elton, in 1927 at age 26, developed a
new concept related to feeding relationships:
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Food is the burning question in animal
society, and the whole structure and
activities of the community are dependent
upon questions of food-supply … animals
have to depend ultimately upon plants
for their supplies of energy, since plants
alone are able to turn raw sunlight and
chemicals into a form edible to animals.
There are, in fact, chains of animals linked
together by food, and all dependent in the
long run upon plants. We refer to these as
“food chains,” and to all the food-chains
in a community as the “food cycle.” (“Food
cycle” became “food web” over the years, but
Elton’s basic concept has otherwise survived
unchanged.)—Ricklefs, 1990, p. 175
These fundamental ideas shape the current
study of ecosystems and the concepts presented
to students in this module.
Although the concepts of food chains and
food webs have been part of the life science
curriculum in the elementary school for years,
we often take for granted what students really
understand about the interactions that occur
within a food web. According to recent research
into children’s learning, students do not
necessarily understand that food chains and
food webs represent the transfer of the Sun’s
energy through all living things in an ecosystem.
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Few students appear to relate their ideas
about feeding and energy to a framework of
ideas about interactions of organisms. Only
half of a sample of undergraduate biology
students, when asked about the statements
“life depends on green plants” and “the
web of life,” explained these statements
in terms of food chains. Only a minority of
these mentioned harnessing solar energy
or photosynthesis as the reason why green
plants are crucial in the food chain. Even
at a tertiary level, many students still
think teleologically: nearly a quarter of
the students expressed views suggesting
that other organisms exist for the benefit
of humans. A subsequent study by Eisen
and Stavy, of students from age 13 up to
undergraduate level, revealed that most
students knew that animals could not exist
in a plant-free world.
However, only 25 percent of biology
students and 7 percent of non-biologists
suggested that this is because animals
cannot make their own food and some
thought that carnivores could exist if their
prey reproduced plentifully.
Adeniyi found that, even after teaching,
13- to 15-year-old Nigerian students were
not convinced that producers exist in
aquatic habitats. These students had little
experience of specific habitats with plants
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living under water. Pupils studied by Leach
and others recognized the existence of
aquatic plants, but some said that sunlight
and carbon dioxide could not get through the
water to the plants and hence they did not
acknowledge these plants as producers.
Smith and Anderson noted that
many of the 11- and 12-year-olds who
accept that populations in a food web
are related may still see predation as
a “specific eating event” for the benefit
of the eater alone. Pupils tended to
regard food which is eaten and used
for energy as belonging to a food chain.
Food which is incorporated into the body
material of eaters was seen as something
different and it was not recognized as
the material which is the food of the next
level.—Driver, et al., 1994, pp. 61–62
This evidence suggests that it is important to
determine what students understand about the
concepts presented in each lesson and to take
time to let students express that understanding
orally and in writing. The more the students
reveal about their thinking, the greater the
likelihood that you can ask focused questions
and frame discussions so that students can
question one another’s viewpoints and evidence
for their ideas.
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The direct study of an ecosystem is important
to the success of the module. Students will
develop a deeper understanding of interactions
within ecosystems if they observe the
interactions or the evidence of interactions
firsthand. The “video adventure” in lesson 1
will help students gain some insights into the
diversity of plant and animal life in the varied
ecosystems throughout the world, but studying
the diversity in their own backyard will have
more meaning to them.
The study of ecosystems is a wonderful way
to get elementary students interested in science.
They are naturally curious about the world
around them and are fascinated with animals.
By exploring the relationships among the plants,
animals, and nonliving things in their own
environment, they can find out about natural
systems and extend their understanding of the
survival needs of plants and animals presented
in previous modules, Investigating Animals
and Their Needs and Investigating Plants. By
reading about and viewing diverse ecosystems,
they can compare the interactions within their
local environment with those in systems far
removed from where they live. They develop
an appreciation for the variety and complexity
of the natural world by learning about the
connections within and among ecosystems.
Investigating Ecosystems provides
experiences that allow students to construct
an understanding of the how living things meet
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their needs for energy (food), water, shelter,
and space through a planned sequence of
activities. The module also provides students
with insights into the interdependence and
balance of living organisms and nonliving
factors in all ecosystems. To understand the
concepts presented, however, students need
adequate time to process what they are learning
by sharing their ideas in their notebooks, in
their teams, and with their classmates. All
along the way, you should take time to talk with
individual students and probe their thinking
about energy flow in food chains; the structure
of food webs; what the terms producer,
consumer, and decomposer mean to them; and
what they describe as interactions between
living and nonliving things.
As they work through the activities, students
develop an awareness of the overall results of
interactions within ecosystems. They recognize
that energy flows from the Sun to producers,
and subsequently through food webs to
consumers in all ecosystems. (Although we
mention the term, we do not expect students
to develop an in-depth understanding of
the process of photosynthesis—the process
plants use to manufacture their own food or
energy supply. To understand the concept of
photosynthesis fully, students would need many
experiences and explanations that this module
does not provide. A complete understanding of
the photosynthetic process is not necessary or
appropriate for this grade level. We intend for
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students to understand the general nature of
the role of the Sun and plants in the transfer of
energy through food chains and food webs, but
not the mechanism by which plants convert the
Sun’s energy into usable food energy.)
Ideally throughout the module, students will
explore an outdoor, natural ecosystem that
is within walking distance of the school. This
ecosystem can be the school yard, a nearby
vacant lot, a pond, a wetland, a wooded area, or
a park. Students will also establish aquariums
for classroom study. We encourage you to
consider establishing other (one or more) “study
systems” within the classroom with which
students can interact if an outdoor study site is
not feasible. The idea is to provide students with
firsthand experiences with ecosystems and the
interactions that take place within them. Direct
observation of classroom and outdoor systems
enables students to experience, not just read
and talk about, interactions within ecosystems.
As students participate in and discuss the
activities, they begin to recognize similarities
and differences among ecosystems. While being
introduced to key concepts in ecology, students
also learn skills important to scientists, such
as making careful observations, recording
observations accurately, and sharing ideas to
further their understanding.
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Consequently, to help students construct an
understanding of the concept of an ecosystem,
the module does the following things:
•
It raises questions.
•
How do plants and animals interact in
different places?
•
How do living things interact with
nonliving things?
•
How do nonliving things interact with other
nonliving things?
•
Why do components of the natural world
interact?
•
It enables students to explore systematically
and to summarize interactions within
different ecosystems. They can use the
regularity of the interactions they find to
make generalizations about interactions in all
ecosystems.
•
It encourages students to confront their prior
ideas and to speculate on the purpose of
interactions in the natural world.
•
It extends students’ understanding of the
natural world by providing experience with
ecological concepts and principles.
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•
It allows students to make predictions about
changes within ecosystems based on their
understanding of the interactions within
those systems.
In addition to enabling students to construct
their understanding of ecosystems, the lessons
in this module provide students with
•
hands-on, minds-on learning experiences;
•
critical-thinking and inquiry skills;
•
conceptually developmental and sequenced
experiences;
•
literacy strategies in reading, writing,
listening, and speaking;
•
opportunities to learn collaboratively with
other students; and
•
integrated activities that encourage curiosity
and imagination.
See “Module at a Glance” for a summary of the
lessons and the development of the concept of
ecosystems.
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Conceptual Outcomes
The following table illustrates the priority
placed on conceptual development in the
module and also displays the correlation of the
module’s conceptual outcomes with the content
standards in the National Science Education
Standards and the Benchmarks for Science
Literacy.
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