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. [Italics added for emphasis.] 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.

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Copyright September 2007 — The Ohio State University. This material is based upon work supported by the National Science Foundation under Grant No. 0424671. 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.

This work is licensed under a Creative Commons License.