Chapter 2

Ecological Background — Setting a Foundation

What do building a house and teaching natural resources to children have in common? To be successful, both must be built on a steady, sturdy and reliable foundation. This chapter will provide you with that foundation. It’s up to you, the outdoor leader, to build on from there!

“I went to the woods, because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach, and not, when I came to die, discover that I had not lived.” — Henry David Thoreau


Ecology is a word we hear often, on the radio and television, in newspapers and in magazines. The word comes from the Greek “oikos,” meaning “house” or “place to live,” and “ology,” meaning “the study of.” Ecology, then, is the study of living things, where they live, and how they interact, both with each other and with their environment. Ecologists look for interrelationships among plants, animals, people and the environment.

The basic unit of ecological study is the ecosystem. Ecosystems have two types of components — living and nonliving. The nonliving parts, the sun, air, water and soil, provide energy, nutrients and other basics of life to the living organisms.

The living organisms can also be grouped into categories, based on their function. Producers, or green plants, are the basic energy source for all other organisms. Consumers get their energy directly from plants (herbivores), from other animals (carnivores) or from both (omnivores). Decomposers, such as fungi and bacteria, are the clean-up crew, recycling plants and animals so that they can be used again by the plants.

Ecosystems are self-sustaining; they can run by themselves. They vary in size from a tiny pond to the Atlantic Ocean, or from a daisy to the great spruce and fir forests of northern Maine. Collectively, the earth’s ecosystems are called the biosphere, that thin, fragile mantle of life that extends from a few feet below the soil surface to several miles above it. It is the only place in the universe known to support life. Ecologists usually study fairly small ecosystems, such as ponds, marshes, forests, fields and intertidal zones.

Let’s take a look at each of the basic components of an ecosystem.


Soil and rocks cover the Earth’s land surfaces. Soil is derived from small rocks, pebbles, mineral particles, organic matter (decaying animal and plant parts), living organisms, air and water. Soil has varying textures depending on the size of the particles that make it up. Particles are classified as sand (large, coarse), silt (medium) and clay (fine, microscopic).

Water and nutrients are found in the spaces between the soil particles. If the spaces are large, as in sandy soils, water and nutrients flow so quickly through the soil that they are not readily available to plants, and the spaces are mostly full of air. If the spaces are very small, as in clay soils, water and nutrients quickly fill all the spaces, keeping air from entering. Adding sand, silt and small rocks to clay soils helps them drain better and keeps them from compacting as easily. Most soils are a combination of sand silt and clay. This means that water, nutrients and air are all held within the soil and are available to plants.

Ideal Mineral Composition of Loam Soil
SAND – 40 percent
SILT – 40 percent
CLAY – 20 percent
Ideal Soil Composition for Plant Growth
SAND – 45 percent
SILT – 25 percent
CLAY – 25 percent
ORGANIC MATTER – 5 percent

Soils are not the same throughout a given area. Soils vary, even within the same yard or field. As you dig down into soil, you may see layers. These layers, called “horizons,” are identified by letters. Most untilled or uncultivated soil has four distinct horizons.

The upper layer, called the 0 horizon, is made up of organic matter, including decayed leaves, grass and animals. The second layer, called the A horizon, is the most fertile growing area. It is often called topsoil. There is some organic matter in this area, as well as most of the creatures that live in the soil. In a cultivated field, the 0 horizon does not exist and the A

The next layer is the B horizon. It generally has more clay, very little organic matter and is less fertile. There may be some small rocks in this area. Rocks in a cultivated field might tell you that the A layer is gone and has been replaced by soil from the B horizon. Excessive cultivation can cause erosion, washing away the soil layers, and exposing more rocks.

The lowest soil layer is the C horizon. This is called the parent material. It is very rocky and has very low fertility. Below the C horizon is the bedrock, the layer of solid rock that lies beneath the soil.

The depth of each soil layer depends on the soil’s age and the climatic conditions that formed the soil. Layers are sometimes different colors, though this is not always true. To better understand soils and their role in ecosystems, try the exercises in Appendix E.


Because you can’t see, taste or touch air, you don’t pay much attention to it, even though it is all around you. Imagine the world without air. There would be no wind, no clouds, no rain, no sound, no fire, no plants, no animals, no you. The Earth would be very much like the moon.

Surrounding the Earth is a thin blanket of air called the atmosphere. The atmosphere is made up of several different gases, small solid particles, and tiny droplets of water and other liquids. These molecules of solids, liquids and gases exert a combined pressure on the Earth. Though you don’t notice it, every square inch of your body is under the pressure of a column of air over 1,000 miles high! That column of air weighs 14.7 pounds at sea level and is called “atmospheric” or “barometric” pressure. At higher elevations, air weighs less because the column of air is shorter and the spaces between the particles are larger.

Air moves over the surface of the Earth. We feel that movement as wind. Why does air move? When air is warmed it becomes lighter and rises, just like a helium balloon rises because the gas inside it is lighter than the surrounding air. The space below the rising column of air is filled with cooler, heavier air. That movement of air is wind. Wind plays an important role in the Earth’s weather and climate. Air warms and rises around the equator. When it reaches the upper levels of the atmosphere, it is forced to move toward the North and South Poles where it cools and moves back down toward the surface of the Earth. At the same time, cool air from the poles is moving along the surface of the Earth, filling in the space under the warm air that is rising at the equator. This pattern of air movement is also affected by the rotation of the Earth and other factors such as mountain ranges and deserts that affect air movement, warming and cooling.

To better understand air and its role in ecosystems, try the exercises in Appendix E.


Water is the second most important substance in your life, second only to the air you breathe. Your body is about 60 percent water. You can live only minutes without air, and only a day or two without water. An average person drinks 23,000 ounces (182 gallons, or 1,500 pounds) of water every year. This is equal to about eight, eight-ounce glasses of water a day.

Water is made up of two atoms of hydrogen (H) and one atom of oxygen(O) — H2O.

Water can be found in all three states of matter: solid (ice), liquid (water) and gas (water vapor or steam). Water must be at or below 32 degrees Fahrenheit (F) or 0 degrees Celsius (C) to be in the solid form. This temperature is called the freezing point, the point at which water (liquid) changes into ice (solid). When frozen, the volume of water increases, but the weight remains the same. This is why icebergs and ice cubes float. For most other substances, the solid form takes up less space than the liquid form. It is a special characteristic of water that it expands when it freezes.

Water has other unique characteristics. Pure water has no smell, taste or color. The liquid and gaseous forms can be compressed, or squeezed into a smaller space, but ice, the solid form, cannot. The surface of liquid water consists of tightly bonded water molecules. It is this “surface tension” that water striders and other insects make use of so that they can walk on water.

At 212 degrees F (100 degrees C), the molecules of liquid water are moving so fast that they escape into the air as gaseous water vapor. This temperature is the boiling point of water. Water can evaporate, or change from a liquid to a gas at any temperature (that’s why the ice cubes in your freezer shrink), but it cannot remain a liquid after it has reached the boiling point. Water vapor is invisible. If water vapor cools so that the molecules slow down a little, the vapor changes back into a liquid. This is called condensation. When water vapor condenses into very small water droplets, we see it as clouds, or our breath on a cold day, or a small cloud over a boiling tea kettle. There are approximately 50,000 tons of water in the atmosphere above a square mile of land on an average day. That’s more than a half a gallon over every square foot!

To better understand water and its changing states, try the exercises in Appendix E.

These three elements, soil, air and water, are the primary non-living components found in an ecosystem, the building blocks that set conditions for life. Energy to power the system originates from the sun, is captured by plants and moved along to other organisms. Let’s take a look at the three primary living groups: producers, consumers and decomposers.


Producers, more commonly called plants, create their own food through a process called photosynthesis. “Photo” refers to the light energy of the sun, while “synthesis” refers to putting things together. In the simplest of terms, photosynthesis is making food with light. Plants “produce” themselves from the sun’s energy. In reality, the process is much more complex.

In each plant, whether it is a giant redwood or microscopic plankton, there exist pigments called chlorophyll. These pigments give leaves their characteristic green color. But more importantly, the chlorophyll acts as a sun trap to collect light energy that hits its cells. This energy is what powers the process. It is while this light energy is trapped within the chlorophyll that water (H2O) and carbon dioxide (CO2) combine and produce glucose (food), with oxygen as a waste product. Why and exactly how all this occurs remains a biological mystery. One thing is certain, however, plants with chlorophyll are the only living things that have this ability. All other life forms are in debt to plants for the miracle of photosynthesis that produces food and oxygen. Plants are crucial in supporting and maintaining all living things.


Consumers are organisms that are unable to create their own food and must eat (consume) other organisms. All animals are included in this group and can be put into one of three categories:

  1. Herbivores — eat primarily plants (mallard ducks, mice, deer, sparrows, aphids)
  2. Carnivores — eat primarily meat (wolves, eagles, trout, spiders)
  3. Omnivores — eat both plants and meat (bears, robins, skunks, humans, snapping turtle)


The most common decomposers are fungi, such as mushrooms and bracket fungus, and bacteria. They break down the complex substances that make up dead plants and animals into simple materials, such as carbon dioxide, water, and minerals. These are released back into the environment where they are used again by plants. Thus, the non-living parts of the ecosystem contribute to living forms that eventually die and return nutrients to the soil. These nutrients become new plant growth, continuing the cycle of life and death.


Ecologists often speak of the living parts of the ecosystem as a biotic community. Community members are bound together through a series of self-sustaining interactions and interrelationships. For instance, different organisms are connected in food chains, and all of the food chains in a community make up an interwoven food web. Each organism lives in a specific habitat (home) that provides food, water, cover and space. What an organism does in a community, its functional role, is called its niche. For example, part of the niche of a squirrel is to collect and store nuts. The forgotten ones often grow into new trees. You can think of the habitat as the “address” of the organism, and its niche as its “profession.”

In some communities, one or several species may be dominant. Dominant species are usually plants. The dominant plants are the ones that convert the most solar energy, moderate the climate and often provide most of the food and shelter available to other organisms. Communities are often named for their dominant species, for example, the spruce-fir forest of northern Maine.


The biosphere is that thin layer on the surface of the Earth that supports life. All living things form unique interrelationships and interdependencies with other organisms and with their surrounding environment.

An ecosystem is composed of non-living parts (sun, soil, air and water) and living parts (producers, consumers, and decomposers).

Life and death maintain a flow of energy and a cycle of nutrients among non-living and living parts of an ecosystem.

Communities are composed of the living members of an ecosystem. These members live in specific habitats and occupy a niche, playing particular roles in the community.