MiddleSchoolPortal/Populations and Ecosystems

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Populations and Ecosystems - Introduction

What do the Mojave Desert, a teaspoon of soil, a stream, a mature oak tree, an iceberg, a school playground, and an animal carcass have in common? Give up? They are all ecosystems supporting a number of populations.

An ecosystem is defined by the U.S. Fish and Wildlife Service as

. . . a geographic area and all its living components (e.g., people, plants, animals, and microorganisms), their physical surroundings (e.g., soil, water, and air), and the natural cycles that sustain them (e.g., precipitation, drought, fire, grazing). The term ecosystem was coined in 1935 by the British ecologist Sir Arthur George Tansley, who described natural systems in "constant interchange" among their living and non-living parts. From " What is an Ecosystem?" Retrieved June 27, 2007.

The U.S. Fish and Wildlife Service is interested in macroecosystems ranging from shallow streams to watersheds the size of the Mississippi River's. But many other groups and individuals are interested in smaller sized ecosystems. For example, when forensic scientists are estimating a time of death, the ecosystem of interest is limited to the body under investigation. An agronomist may be interested in the ecosystem of a teaspoon of soil, and a microbiologist in the ecosystem of an animal's gut. This variety in ecosystem size and scope means you can engage your students in a study of ecosystems and populations no matter what your context is or resource limitations are.

The ecosystem concept is rather complex, but students often find these interactions interesting and are usually easily engaged in ecosystem studies. You can then capitalize on student curiosity by providing a learning environment conducive to inquiry. (See the National Science Education Standards section of this publication for how populations and ecosystems align with the content standards.)

It's always a good idea when introducing a new topic to start with what students know and build a bridge from there to the new content. Your students may be familiar with the water, carbon, and nitrogen cycles and probably have some knowledge of weather, including humidity, patterns of precipitation, and natural disasters such as volcanic eruptions, floods, hurricanes, and earthquakes.



As a means of activating prior knowledge, you might ask: Have you ever driven past a cattle farm on a hot summer day? Describe what the cattle were doing, and how and where they had gathered. Have you ever fished in a stream or river? When is the best time of day to do that and where do you drop your bait and why? Are the tall trees seen in forests in this area likely the same as those 1,000 miles north or south of us? Why?

As a means of pre-assessment, ask students (rewording and ordering these questions as you wish and withholding feedback regarding correctness) if the abiotic factors of carbon, water or nitrogen or any weather or earth processes impact populations of living things in any way? If not, why not? If yes, how? Can one group of organisms — plant, animal, bacteria or protist — affect another? For example? How about within a given population: can some members of the same species and population affect others of their own species and within their own population? Can living things alter their physical or chemical surroundings? If no, why not? If yes, how?

Student responses can be written in a notebook or recorded on chart paper and revisited at the end of the unit. Students can compare their initial knowledge to their new knowledge and revise the initial responses accordingly. In this way, they have concrete evidence of their progress and knowledge gained.

A possible hook to begin your unit is the intriguing video clip of leafcutter ants on the PBS Evolution web site. Though the video is embedded in a lesson on the nature of science, it highlights the ecology and biology of the species, making a perfect segue to a unit exploring populations and ecosystems.

Since many schools have access to streams, one section of this publication is devoted to stream ecology. For those who lack access to a stream, we provide resources which focus on classroom-based microecosystems and terrestrial ecosystems. Finally, we provide resources that will enable you and your students to put new-found knowledge of populations and ecosystems to work by investigating current issues in ecology.

Background Information for Teachers

The National Science Education Standards include basic themes that cut across any science unit we teach. The themes are: systems, models, patterns of change, constancy and scale. In a study of ecosytems these themes emerge loudly and clearly. To see some learning progressions focused on these themes go to the AAAS Project 2061 Science Literacy Maps under the Common Themes heading.

There are also content focused science literacy maps. They map a sequence of learning goals from grades K-12 and provides access to related resources. These maps illustrate connections between concepts and across grade levels. An image of the middle grades (6-8) only part of the Interdependence of Life Map appears below. Clicking on a concept within the maps will show NSDL resources relevant to the concept, as well as information about related AAAS Project 2061 Benchmarks and National Science Education Standards. Move the pink box in the lower right hand corner of the page to see the grades 6-8 learning goals.

Interdependence of Life Map

View individual map Printable view of map

If you are required to teach about ecosystems and populations and you did not major in ecology, do not despair! This section highlights resources intended for teachers or college or high school ecology students. They contain content as well as illustrations, graphs, photographs, and examples of the important concepts in population ecology and ecosystems. In exploring these resources you will enhance your content knowledge, enabling decisions regarding which ecology topics will be both interesting and beneficial to your students.

Connecting Urban Students with Their Rivers Generates Interest and Skills in the Geosciences An overview of two enrichment programs for urban high school students from Hartford, Connecticut, is provided here. The programs were designed to expose students entering the tenth grade to earth science as a problem-solving science. Developers focused on understanding watersheds and water quality, primarily using chemical techniques on samples collected from the Connecticut River and adjacent waters. The students worked in groups and student-faculty ratios did not exceed three to one. The majority of the students indicated that the programs were a positive experience and that they developed a greater appreciation for science.

Sustainable Forest Ecosystems in the Central Appalachians This title page contains a link to Research Problems, a one-page reference about real ecological issues in forest management — helpful background if your school is near a forested area and you are considering an authentic learning experience for your students.

Earth on Edge: Ecosystems This PBS site provides information about the six ecosystems on which life on earth most heavily depends: agricultural, forest, freshwater, grassland, coastal, and urban. Ecosystems are described as communities of interacting organisms and the physical environment in which they live. The goods and services that ecosystems provide are said to form the foundation of human economies. Ecosystems purify air and water, help to control climate, and produce valuable soil services. Site users may access a discussion guide to accompany the video of the television program, which can be used in colleges, secondary schools, and community groups. Case studies are taken from the companion book, People and Ecosystems: The Fraying Web of Life, and from Pilot Analysis of Global Ecosystems: Agroecosystems (World Resources Institute). The online text includes profiles and ecosystem assessments, which you can adapt to fit your teaching context with references to ecosystems around the world. A list of additional resources includes links to environmental organizations, books, and periodicals.

The State of the Nation's Ecosystems A comprehensive report prepared by experts from businesses, environmental organizations, universities, and federal, state, and local government agencies is an overview of what the nation most needs to know about the changing state of its ecosystems. The report offers information from research in many fields and is organized into chapters covering coasts and oceans, farmlands, forests, fresh waters, grasslands and shrublands, and urban and suburban areas. The entire report may be searched by keyword, and each chapter may be downloaded. This web site can inspire numerous ideas for student research into current ecological issues in your own community.

Biological Indicators of Watershed Health This resource provides links to many resources pertaining to freshwater and marine ecology. Particularly informative is the common freshwater benthic macroinvertebrates link at the bottom of page, which contains numerous photographs of the relevant organisms.

Lessons on Stream Ecology

Many state departments of natural resources have outreach programs in which they work with school groups to survey local streams’ biodiversity and abiotic conditions. The departments often have the necessary equipment as well. The activities provided here can stand alone or complement projects done with the assistance of natural resources personnel.

Ecology of a Stream: A Tale of Balance An overview of the ecology of a stream, including information pertaining to temperature and turbidity, energy balance, water balance, and the food chain.

Freshwater Ecosystems This site is divided into three segments: rivers and streams; ponds and lakes; and wetlands, providing information, photos, and graphics related to freshwater resources. The site provides information about the geology and biology of these ecosystems and some information on technology as well. Each of the three segments contains links to additional resources related to that topic. Students could readily use the site as a resource for independent learning or research, and teachers could use the site to develop water-related activities. For example, students could be divided into research teams, one per segment, and each team could subdivide to investigate the links within its segment. Then students could be responsible for teaching others about their topic, and learning from others about the other topics. Finally, students would identify the relationships among all topics. Alternatively, students could use the site as inspiration for forming questions for professionals, such as natural resources employees or ecology research scientists.

Nab the Aquatic Invader Major arrests need to be made in the fight against invading aquatic plants and animals. These invaders have hitchhiked to U.S. waters and are on the loose, creating huge problems, such as impacts on biodiversity. Students can be private investigators on the case and help the other detectives “book the bad guys.”

Ohio Stream Quality Monitoring Project Interested in authentic ecology experiences for you and your students? This page provides an overview of Ohio’s program, which enlists volunteers in the collection of water sampling data. Following a free, short workshop, individuals and groups are given easy-to-use equipment and assigned to one or more stream stations. Volunteers, working in teams of two or more, examine small, riffle areas of stream bottoms and use fine mesh nets to collect macroinvertebrates. Volunteers are taught how to identify these tiny organisms and record their findings. A contact link is provided if you need advice on how to start a similar program in your area.

Lessons on Micro and Terrestrial Ecosystems

The activities presented here can be conducted in classrooms or on school grounds.

The Race of Microorganisms This article explains how lactic acid bacteria grow in a pickle crock to digest sugars in the cucumbers and produce lactic acid. Not only does this acid give the pickles their characteristic sour tang, it controls the spread of spoilage microbes. The pickle crock is an ecosystem. Your students can identify and describe the interactions between the abiotic factors, such as salt concentrations, pH and temperature, and the biotic factors: the various microorganisms. In doing so, students should discover that the activities of living things can alter the environment, thus impacting the potential biodiversity of a given ecosystem and illustrating the dynamic versus static nature of ecosystems.

Oh Deer! Two fundamental concepts in ecology — population dynamics and the interdependence of animal life and the environment — are illustrated in this lesson. Written for grades 4-6, the lesson can be adapted for older students by requiring them to graph the data collected, interpret the graph, infer causes for the observed effects, and research additional populations to ascertain whether what they observed in this activity is also true for other kinds of populations. The objectives of the lesson are: students will be able to identify and describe food, water and shelter as three essential components of habitat; describe the importance of good habitat for animals; define limiting factors and give examples; and recognize that some fluctuations in wildlife populations are natural as ecological systems undergo a constant change.

Ecosystems This lesson plan focuses on biodiversity within ecosystems and within species. Students collect leaves to demonstrate how diverse life can exist within a small area. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, an audio-enhanced vocabulary list, and links to teaching tools for making quizzes, worksheets, and puzzles. A video, available to order, complements this lesson. MSP full record

Forest Food Webs This lesson plan is part of the library for grades 6-8. It focuses on the seasonal changes that affect life in a temperate forest ecosystem and how organisms are dependent on one another for proper nutrition. Students describe the three major types of organisms that live in an ecosystem: producers, consumers, and decomposers. They then create a food web diagram for display in the classroom. Included are objectives, materials, procedures, discussion questions, evaluation ideas, suggested readings, vocabulary, and links to teaching tools for making quizzes, worksheets, and puzzles. Videos, available to order, complement this lesson.

Ecosystem: Analyzing an Ecosystem This is an interactive animation where students review and reinforce their knowledge of ecological concepts, such as abiotic and biotic interactions and biotic relationships, and vocabulary.

Trees, Soil and Water: Journey to Forever The crops that feed the cities are raised in the valleys and flat river plains, but the fate of the valleys is decided in the hills and mountains where the streams rise. This article explains that where the hill slopes and ridges in the upper reaches are covered with trees, the streams flow clearly. It shows that when the trees are gone, the soil washes down the slopes to clog the streams, foul the river bottoms, and allow flooding.

Ecological Footprint: Human Populations

The first three resources are short (two minutes) broadcasts from the radio program Pulse of the Planet featuring an expert on the ecological footprints of nations and individuals. Analogies are used, rendering the concepts easily comprehensible to middle school students. We suggest you use the broadcasts in the order they are presented due to the relationships of the concepts involved. Each broadcast is 49¢. Following the broadcasts is a lesson in which students investigate the "size" of their own ecological footprint. The lesson, however, could just as easily precede listening to the broadcasts.

Ecological Footprint: The Role of Technology The director of the sustainability program for the public policy group Redefining Progress discusses the concept of ecological overshoot. He reminds us that today we use more than what nature can regenerate, and that as long as we use more, we are depleting the natural capital and liquidating our most essential assets.

Ecological Footprint: Only One Planet This segment discusses the ecological footprint of individuals, or the amount of nature it takes to support their lifestyle. The speaker explains that if we divide up the total ecologically productive space on the planet by the number of people, what we get is five acres per person. In the United States, on average, we use about 25 to 30 acres per person to provide all of our services.

Ecological Footprint: Overshoot The speaker says that ecological overshoot can continue for a while, but eventually someone will have to pay with a lower standard of living.

Issues in Ecology

This section presents a few issues in ecology; many are authentic cases to which your students should be able to relate after studying concepts in ecology. Investigation of one or more of the issues can serve as a formal, summative assessment, depending on how you frame it. National Park Service Nature and Science: Critical Issues] Parks are becoming crowded remnants of primitive America, threatened by invasions of nonnative species, pollution, and incompatible uses of resources in and around parks. Read more about some of the critical issues facing our parks system and what the National Park Service is doing to address them.

Invasive Species: Background Information In two paragraphs, this resource introduces readers to the concept of invasive species. Purple loosestrife is given as an example of one of the many invasive species that is not indigenous to North America. The resource reveals the proportion of nonnative species that have turned out to be invasive in North America. The magnitude of ecological and monetary damage caused by invasive species is also mentioned. Links are given to web sites with more information about invasive species.

Talking Trash about the Ocean In this lesson, students create an advertising campaign to raise awareness about the importance of keeping trash out of the marine ecosystem. Students work in teams to create different campaigns geared toward particular target audiences and produce posters. We suggest modifying the assessment to include applying knowledge of ecosystems and population ecology and demonstrating proficiency with some specified concepts of your choice. Links to additional information and resources are also provided.

Rainforest Facts This page is a nicely organized reference with headings such as: The Wealth of the Rainforests; The Biodiversity of the Rainforest; Logging for Tropical Hardwoods; Fuel Wood and the Paper Industry; Subsistence Farming; Bioprospecting; and Indigenous People, A Valuable Resource. You could develop a webquest around it, or assign jigsaw groups of students to different topics with the goal of learning enough about the topic to teach other students. In doing so, students demonstrate mastery of ecological concepts in a real-world application.

SMARTR: Virtual Learning Experiences for Students

Visit our student site SMARTR to find related virtual learning experiences for your students! The SMARTR learning experiences were designed both for and by middle school aged students. Students from around the country participated in every stage of SMARTR’s development and each of the learning experiences includes multimedia content including videos, simulations, games and virtual activities. Visit the virtual learning experience on Ecosystems.


The FunWorks Visit the FunWorks STEM career website to browse science-related careers, including meteorologist, environmental scientist, and marine biologist.

Latest Science News from the New York Times

NYT > Endangered and Extinct Species

News about Endangered and Extinct Species, including commentary and archival articles published in The New York Times.

NYT > Environment

News about Environment, including commentary and archival articles published in The New York Times.

National Science Education Standards

Here we point out the various content standards of the National Science Education Standards that align with the lessons and activities provided in this publication.

Physical Science: Content Standard B

As a result of their activities in grades 5-8, all students should develop understanding of

Transfer of energy

  • Energy is a property of many substances and is associated with heat, light, electricity, mechanical motion, sound, nuclei, and the nature of a chemical. Energy is transferred in many ways.
  • Heat moves in predictable ways, flowing from warmer objects to cooler ones, until both reach the same temperature.
  • Light interacts with matter by transmission (including refraction), absorption, or scattering (including reflection). To see an object, light from that object - emitted by or scattered from it - must enter the eye.
  • The sun is a major source of energy for changes on the earth's surface. The sun loses energy by emitting light. A tiny fraction of that light reaches the earth, transferring energy from the sun to the earth. The sun's energy arrives as light with a range of wavelengths, consisting of visible light, infrared, and ultraviolet radiation.

Life Science: Content Standard C

As a result of their activities in grades 5-8, all students should develop understanding of

  • Populations and ecosystems.
  • A population consists of all individuals of a species that occur together at a given place and time. All populations living together and the physical factors with which they interact compose an ecosystem.
  • Populations of organisms can be categorized by the function they serve in an ecosystem. Plants and some micro-organisms are producers - they make their own food. All animals, including humans, are consumers, which obtain food by eating other organisms. Decomposers, primarily bacteria and fungi, are consumers that use waste materials and dead organisms for food. Food webs identify the relationships among producers, consumers, and decomposers in an ecosystem.
  • For ecosystems, the major source of energy is sunlight. Energy entering ecosystems as sunlight is transferred by producers into chemical energy through photosynthesis. That energy then passes from organism to organism in food webs.
  • The number of organisms an ecosystem can support depends on the resources available and abiotic factors, such as quantity of light and water, range of temperatures, and soil composition. Given adequate biotic and abiotic resources and no disease or predators, populations (including humans) increase at rapid rates. Lack of resources and other factors, such as predation and climate, limit the growth of populations in specific niches in the ecosystem.

Diversity and adaptations of organisms

  • Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.
  • Extinction of a species occurs when the environment changes and the adaptive characteristics of a species are insufficient to allow its survival. Fossils indicate that many organisms that lived long ago are extinct. Extinction of species is common; most of the species that have lived on the earth no longer exist.

Science and Technology: Content Standard E

As a result of activities in grades 5-8, all students should develop

Understandings about science and technology

  • Scientific inquiry and technological design have similarities and differences. Scientists propose explanations for questions about the natural world, and engineers propose solutions relating to human problems, needs, and aspirations. Technological solutions are temporary; technologies exist within nature and so they cannot contravene physical or biological principles; technological solutions have side effects; and technologies cost, carry risks, and provide benefits.
  • Many different people in different cultures have made and continue to make contributions to science and technology.
  • Science and technology are reciprocal. Science helps drive technology, as it addresses questions that demand more sophisticated instruments and provides principles for better instrumentation and technique. Technology is essential to science, because it provides instruments and techniques that enable observations of objects and phenomena that are otherwise unobservable due to factors such as quantity, distance, location, size, and speed. Technology also provides tools for investigations, inquiry, and analysis.
  • Perfectly designed solutions do not exist. All technological solutions have trade-offs, such as safety, cost, efficiency, and appearance. Engineers often build in back-up systems to provide safety. Risk is part of living in a highly technological world. Reducing risk often results in new technology.
  • Technological designs have constraints. Some constraints are unavoidable, for example, properties of materials, or effects of weather and friction; other constraints limit choices in the design, for example, environmental protection, human safety, and aesthetics.
  • Technological solutions have intended benefits and unintended consequences. Some consequences can be predicted, others cannot.

Science in Personal and Social Perspectives: Content Standard F

As a result of activities in grades 5-8, all students should develop understanding of

  • Personal health
  • Populations, resources, and environments
  • Natural hazards
  • Risks and benefits

Personal health

  • Natural environments may contain substances (for example, radon and lead) that are harmful to human beings. Maintaining environmental health involves establishing or monitoring quality standards related to use of soil, water, and air.
  • Populations, resources, and environments.
  • When an area becomes overpopulated, the environment will become degraded due to the increased use of resources.
  • Causes of environmental degradation and resource depletion vary from region to region and from country to country.

Natural hazards

  • Human activities also can induce hazards through resource acquisition, urban growth, land-use decisions, and waste disposal. Such activities can accelerate many natural changes.
  • Natural hazards can present personal and societal challenges because misidentifying the change or incorrectly estimating the rate and scale of change may result in either too little attention and significant human costs or too much cost for unneeded preventive measures.

Risks and benefits

  • Students should understand the risks associated with natural hazards (fires, floods, tornadoes, hurricanes, earthquakes, and volcanic eruptions), with chemical hazards (pollutants in air, water, soil, and food), with biological hazards (pollen, viruses, bacterial, and parasites), social hazards (occupational safety and transportation), and with personal hazards (smoking, dieting, and drinking).
  • Individuals can use a systematic approach to thinking critically about risks and benefits. Examples include applying probability estimates to risks and comparing them to estimated personal and social benefits.
  • Important personal and social decisions are made based on perceptions of benefits and risks.

Read the entire National Science Education Standards online for free or register to download the free PDF. The content standards are found in Chapter 6.

Author and Copyright

Mary LeFever is a resource specialist for the Middle School Portal 2: Math & Science Pathways project, a doctoral candidate in science education at Ohio State University, and presently teaches high school biology. She has taught middle school science and biology and natural sciences at Columbus State Community College.

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Copyright September 2007 - The Ohio State University. Last updated September 19, 2010. This material is based upon work supported by the National Science Foundation under Grant No. 0424671 and since September 1, 2009 Grant No. 0840824. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.