Standard 1: Students will understand that living organisms interact with one another and their environment.

Standard 1, Objective 1: Summarize how energy flows through an ecosystem.

Section 1.1 Ecosystems

Objective:

Explain the interactions among and between biotic and abiotic factors.

Do organisms live in isolation?

No, organisms are not separated from their environment or from other organisms. They interact in many ways with their surroundings. For example, this deer may be drinking from this stream or eating nearby plants. Ecology is the study of these interactions.

All organisms have the ability to grow and reproduce. To grow and reproduce, organisms must get materials and energy from the environment. Plants obtain their energy from the sun through photosynthesis, whereas animals obtain their energy from other organisms. Either way, these plants and animals, as well as bacteria and fungi, are constantly interacting with other species as well as the non-living parts of their ecosystem. An organisms environment includes two types of factors:

Abiotic factors are the parts of the environment that are not living, such as sunlight, climate, soil, water, and air.

Biotic factors are the parts of the environment that are alive, or were alive and then died, such as plants, animals, and their remains. Biotic factors also include bacteria, fungi and protists.

Ecology studies the interactions between biotic factors, such as organisms like plants and animals, and abiotic factors. For example, all animals (biotic factors) breathe in oxygen (abiotic factor). All plants (biotic factor) absorb carbon dioxide (abiotic factor) and need water (abiotic factor) to survive.

FOOD FOR THOUGHT

Can you think of another way that abiotic and biotic factors interact with each other?

Ecosystems can be studied at small levels or at large levels. The levels of organization are described below from the smallest to the largest:

A species is a group of individuals who are genetically related and can breed to produce fertile young. Individuals are not members of the same species if their members cannot produce offspring that can also have children. The second word in the two-word name given to every organism is the species name. For example, in Homo sapiens, sapiens is the species name within the Homo genus.

A population is a group of organisms belonging to the same species that live in the same area and interact with one another. A community is all of the populations of different species that live in the same area and interact with one another. An ecosystem includes the living organisms (all the populations) in an area and the nonliving aspects of the environment. An ecosystem is made of the biotic and abiotic factors in an area.

Ecologists study ecosystems at every level, from the individual organism to the whole ecosystem and biosphere. They can ask different types of questions at each level. Examples of these questions are given in Table below, using the zebra (Equus zebra) as an example.

Level

Question

Individual

How do zebras keep water in their bodies?

Population

What causes the growth of zebras populations?

Community

How does a disturbance, like a fire or predator, affect the number of mammal species in African grasslands?

Ecosystem

How does fire affect the amount of food available in grassland ecosystems?

Biosphere

How does carbon dioxide in the air affect global temperature?

SUMMARY

Ecology is the study of how living organisms interact with each other and with their environment.

Abiotic factors are the parts of the environment that have never been alive, while biotic factors are the parts of the environment that are alive, or were alive and then died.

Levels of organization in ecology include the population, community, ecosystem, and biosphere.

An ecosystem is all the living things in an area interacting with all of the abiotic parts of the environment.

EXTENSION

Use the resource below to answer the questions that follow.

A Study in Stream Ecology at USGS

http://gallery.usgs.gov/videos/449 - .UKWeJId9KSo(6:57)

1. What are some of the abiotic factors that scientists monitor when dealing with stream ecosystems?

2. What are some of the biotic factors that scientists monitor when dealing with stream ecosystems?

3. Remembering what you've learned about the scientific process, why is it valuable for scientists to use the same procedures and gather the same information across different streams and a wide ranging geography? What does this allow them to do? How does this affect the strength and applicability of their research?

4. What is a "benchmark" in ecology? Why are they essential?

5. Why is it important to have a reference stream if you want to gauge the effects of Homo sapiens on streams? What characteristics should this reference stream have?

6. How does water pollution seem to be affecting diversity in some streams? What data would be necessary to prove the pollution is the causative agent affecting stream biodiversity?

REVIEW QUESTIONS

7. What do ecologists study?

8. In a forest, what are some biotic factors present? Abiotic factors?

Section 1.2:

Food Chains and Food Webs

Objective

Summarize how energy flows through an ecosystem through food chains and food webs.

Who eats whom?

To survive, one must eat. Why? To get energy! Food chains and webs describe the transfer of energy within an ecosystem, from one organism to another. In other words, they show who eats whom.

Food chains and food webs are diagrams that represent feeding relationships. They show who eats whom. In this way, they model how energy and matter move through ecosystems. Food chains always begin with producers, organisms that can make their own food through photosynthesis, such as the plants in the figure above. Consumers are organisms that cannot make their own food and must get energy from other living things, such as the lion in the figure above. Consumers can be herbivores, carnivores, or omnivores. Food chains might also include decomposers that get nutrients and energy by breaking down the remains of dead organisms or animal waste. Bacteria and fungi are good examples of decomposers. Through the process of decomposition, they recycle nutrients like carbon and nitrogen back into the environment so producers can use them.

FOOD FOR THOUGHT

What would happen in an environment if there were no decomposers?

A food chain represents a single pathway by which energy and matter flow through an ecosystem. An example is shown in Figure below. Food chains are generally simpler than what really happens in nature. Most organisms consumeand are consumed bymore than one species.

This food chain includes producers and consumers. How could you add decomposers to the food chain?

Is the caterpillar shown in the food chain an herbivore, carnivore, or omnivore? How do you know?

A food web represents multiple pathways through which energy and matter flow through an ecosystem. It includes many intersecting food chains. It demonstrates that most organisms eat, and are eaten, by more than one species. An example is shown in the Figure below.

FOOD FOR THOUGHT

This food web consists of several different food chains. Which organisms are producers in all of the food chains included in the food web?

Draw one food chain out of this food web.

SUMMARY

Producers make their own food through photosynthesis.

Consumers must obtain their nutrients and energy by eating other organisms.

Decomposers break down animal remains and wastes to get energy.

Food chains and food webs are diagrams that represent feeding relationships.

Food chains and webs model how energy and matter move through ecosystems.

EXTENSION

Use the resource below to answer the questions that follow.

Decomposers at:

http://www.youtube.com/watch?v=Z6V0a_7N1Mw (3:19)

1. What is the role of decomposers in an ecosystem? What is the source of the matter that is decomposed?

2. How do the actions of earthworms improve soil quality? How does this impact the amount of biomass an ecosystem can support?

3. How do gastropods function as decomposers?

REVIEW QUESTIONS

4. How are food chains and food webs the same? How are they different?

5. What is the role of producers in a food chain? How do they get their food?

Section 1.3: Energy Pyramids

Objective:

Explain how energy enters, is used, transferred and lost as it moves through organisms in an ecosystem.

How much energy can be gained from the warthog?

If the cheetah is successful in capturing the warthog, he would gain some energy by eating it. But would the cheetah gain as much energy as the warthog has ever consumed? No, the warthog has used up some of that energy for its own needs. The cheetah will only gain a fraction of the energy that the warthog has consumed throughout its lifetime. When an herbivore eats a plant, the energy in the plant tissues is used by the herbivore. But how much of that energy is transferred to the herbivore? Remember that plants are producers, bringing the energy into the ecosystem by converting sunlight into glucose. The plant needs and uses much of that energy. After the plant uses the energy from glucose for its own needs, the excess energy is available to the organism that eats the plant.

The herbivore uses the energy from the plant to power its own life processes and to build more body tissues. How