Nutritional Interactions
All ecosystems must have three basic kinds of nutritional interactions in order to be stable and self-sustaining. These nutritional interactions involve producers and consumers (including the essential decomposers).

A producer organism is one that is capable of trapping the Sun's energy to make glucose sugar in the process of photosynthesis. Plants and algae are examples of producer organisms. Sometimes producer organisms are called autotrophs. Consumer organisms depend upon and eat other organisms for their food. Sometimes consumer organisms are called heterotrophs. Many different categories of consumer organisms exist. A herbivore eats primarily plant material, while a carnivore eats primarily other animals. A predator is a type of carnivore that kills its food. The organism the predator feeds upon is called its prey. A wolf and rabbit would provide an example of a predator/prey relationship. Scavengers feed upon organisms that other organisms have killed. An omnivore is a consumer that eats both plant and animal material. Humans are an example of an omnivore. A decomposer is a special category of consumer organism. Decomposers break down dead organic matter and change it to simpler nutrients which can be recycled in the ecosystem. Bacteria of decay and many fungi are examples of decomposer organisms.
Circle of Life
In order for an ecosystem to sustain life, several conditions must be met.

Some Conditions for a Stable Ecosystem
·  A constant source of energy and a living system capable of incorporating this energy into organic molecules. (This means plants and/or algae are needed to convert solar energy to the energy of sugars by the process of photosynthesis.)
·  A cycling of materials between organisms and their environment.(Some material cycles include oxygen, carbon dioxide, water, and nitrogen.) Decomposers, such as bacteria of decay and some fungi are needed in every ecosystem to return and recycle necessary materials to the environment.

Energy Flow
Energy flows through ecosystems in one direction, typically from the Sun, through photosynthetic organisms or producers, to herbivores to carnivores and decomposers. The chemical elements that make up the molecules of living things pass through food webs and are combined and recombined in different ways. At each link in a food web, some energy is stored in newly made structures but much energy is lost into the environment as heat. Continual input of energy from sunlight is required to keep this process going. Energy pyramids are often used to show the flow of energy in ecosystems.

Food Chains
If an ecosystem is to be self-sustaining it must contain a flow of energy. One way of representing the flow of energy through the living components of an ecosystem is through the use of a food chain. A food chain indicates the transfer of energy from producers through a series of organisms which feed upon each other.

A Food Chain

Note that the arrows in the food chain point to the organisms which are doing the eating. Thus the arrows in the food chain represent the flow of energy through the ecosystem. / The algae and floating plants are the producers in this food chain.
The aquatic crustaceans are the primary consumers which eat the producers.
Fish are secondary consumers eating the primary consumers.
A food chain may also contain third level or other consumers as indicated by the raccoons in this food chain.

Food Webs
In a natural community, the flow of energy and materials is much more complicated than illustrated by any one food chain. A food web is a series of interrelated food chains which provides a more accurate picture of the feeding relationships in an ecosystem, as more than one thing will usually eat a particular species.

A Food Web
Energy flow in a food web also starts with the producer organisms through the various levels of consumer organisms as in a food chain. /

Energy Pyramids
An energy pyramid provides a means of describing the feeding and energy relationships within a food chain or web. Each step of an energy pyramid shows that some energy is stored in newly made structures of the organism which eats the preceding one. The pyramid also shows that much of the energy is lost when one organism in a food chain eats another. Most of this energy which is lost goes into the environment as heat energy. While a continuous input of energy from sunlight keeps the process going, the height of energy pyramids (and therefore the length of food chains) is limited by this loss of energy.

An Energy Pyramid

The picture at the left is an energy pyramid. Producer organisms represent the greatest amount of living tissue or biomass at the bottom of the pyramid. The organisms which occupy the rest of the pyramid belong to the feeding levels indicated in each step. On average, each feeding level only contains 10% of the energy as the one below it, with the energy that is lost mostly being transformed to heat.

Material Cycles
The atoms and molecules on the Earth cycle among the living and nonliving components of the biosphere. Carbon dioxide and water molecules used in photosynthesis to form energy-rich organic compounds are returned to the environment when the energy in these compounds is eventually released by cells through the processes of cell respiration and other life activities. The number of organisms any environment can support is called its carrying capacity. The carrying capacity of an environment is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the remains of dead organisms through the activities of bacteria and fungi. The organisms interact with their nonliving (abiotic) and living (biotic) environment. Living organisms have the capacity to produce populations of unlimited size, but available resources in their environments are finite. This restricts the growth of populations and produces competition between organisms. Ex. Water Cycle

Ex. Carbon Cycle

Ex. Nitrogen Cycle

Organism Relationships
Organisms interactions may be competitive or beneficial. Organisms may interact with one another in several ways. Some of these relationships include producer/consumer, predator/prey, or parasite/host relationships. Other organisms interactions include those in which one organism may cause disease in, scavenge, or decompose another.

Symbiotic Relationships
Close living associations between organisms are called symbiotic relationships. Parasitism is an example of such a relationship. In this situation, the parasite feeds upon the tissues or fluids or another organism, but usually does not kill the organism it feeds upon, as this would destroy its food supply. The organism the parasite feeds upon is called the host organism. An example of this sort of relationship would be fleas on a dog or athlete's foot fungus on a human.

Types of Symbiosis
·  parasitism: the parasite benefits at the expense of the host
·  mutualism: both organisms benefit from the association
·  commensalism: one organism is benefited and the other is unharmed

Some Detrimental Human Activities
Humans are part of the Earth's ecosystem. Human activities can either deliberately or inadvertently alter the balance of an ecosystem. This destruction of habitat, whether accidental or intentional, is threatening the stability of the planet's ecosystems. If these human influences are not addressed, the stability of many ecosystems may be irreversibly affected. Some of the ways that humans damage and destroy ecosystems are indicated in the table below.

Some Ways Humans Adversely Influence Ecosystems
Human Influence / Effect on Ecosystems
Population growth / Our increasing numbers are using excessive amounts of the Earth's limited resources.
Overconsumption / Industrialized societies are using more resources per person from our planet than people from poor nations.
Advancing Technologies / Often we introduce technology without knowing how it will influence the environment
Direct Harvesting / This has resulted in a large loss of rainforest and the many products associated with its biodiversity.
Pollution / Land, air, water, and nuclear pollution have had many adverse influences on ecosystems.
Atmospheric Changes / These include the addition of Greenhouse gases mostly due to the burning of fossil fuels and depletion of our stratospheric ozone layer.
Other pollutants also have negative effects on living things.

1. Match the living parts of an ecosystem with the examples below. Write the correct letter on the line to the right of each example.

A = producer B = primary consumer C = secondary consumer D = decomposer

A tree ______/ A hawk eating a lizard ______/ A squirrel eating a nut ______
A grasshopper eating grass ______/ Bacteria changing dead plants to nitrates ______/ A human eating lettuce ______
A frog eating a grasshopper ______/ Bracket fungi decaying a stump ______

2. Choose the type of symbiotic relationship from the word bank that best matches each statement below.

Word Bank: parasitism mutualism commensalism

a. ______A bird makes a nest in a tree.

b. ______A barnacle attaches itself to a whale and rides along gathering food from the water.

c. ______A leech attaches itself to your leg and sucks blood.

d. ______A cowbird lays its eggs in the nest of a sparrow. The cowbird young are larger and more aggressive than the sparrow young. The mother sparrow feeds the most aggressive young in the nest first. Some of her own offspring may die.

e. ______Clownfish swim among the stinging tentacles of sea anemones without being stung. They often gather tidbits of food left over from a sea anemone’s meal. Clownfish are protected from predators when they are near the tentacles. The clownfish tend to scare off large prey that might eat the sea anemone.

f. ______Spanish moss grows on the limbs of trees but does not obtain moisture or nutrients from the tree.

g. ______Bees, wasps, and flies gather nectar from flowers, and in the process get pollen on their legs. When they leave the flower and go to the next one, some pollen is deposited on the style of the next flower. The flower can then produce seeds.

h. ______Yucca moth larvae can only feed on developing seeds of the yucca and the plant is pollinated only by the yucca moth.

i. ______A tick attaches itself to a dog and sucks the blood of the dog.

j. ______Lungworms live in the lungs of bighorn sheep, some of whom die from this.

k. ______The stomach of a cow is home to a type of bacteria that digests the grass eaten by the cows. Cows cannot digest grass without the help of the bacteria.

l. ______Small protozoa live inside the body of a termite and digest the wood that the termites eat. Without the protozoa, termites would not be able to digest the wood.

m. ______Mistletoe is the green sprig that grows on trees such as oak, where it takes nutrition from the tree, weakening it.

n. ______Cowbirds eat seeds and insects. They follow grazing buffalo and cows to eat the insects which jump and fly as the animal’s hooves kick at the grass.

3. Use the diagram of the ocean food web below to answer the questions

Create a food chain from the web shown above:

Create an energy pyramid from the web shown above:

What percentage of energy is passed on to each trophic level?

Is the energy transferred and lost or cycled? ______

What are 3 materials that are cycled in an ecosystem? ______

Which of these organisms is not an omnivore?

A herring B shrimp C blue whale D killer whale

4. The energy pyramid below shows the flow of energy through the organisms in a Connecticut river.

Which of these organisms are the autotrophs in the river ecosystem? A algae B minnows C trout D zooplankton

If the trout population were over fished, which population of organisms would most likely increase as a direct result?

A algae B minnows C trout D zooplankton

Which level of the pyramid represents the largest percentage of available energy?

A algae B minnows

C trout D zooplankton

According to the pyramid, what is the niche (role) of the trout?

A autotroph

B carnivore

C herbivore

D primary consumer