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Ecosystems and Ecology

Updated on October 1, 2014
Deer | Source

Ecosystems: What Are They and How Do They Work?

An ecosystem is made up of all the different species that live together in one habitat, along with all the physical aspects (soil, water, weather, etc.) of that habitat.

Why do scientists study ecosystems? To learn about how things are connected, as well as what humans can do to better protect the environment. But why protect the environment? Because what affects one part of the environment, affects us all. When even just one species becomes extinct or is brought into new areas with no natural predators, unpredictable changes can take place.

In this unit on Ecology, we'll explore the subject of ecosystems. What are they? How do they change? How does energy flow through them? What are food chains, food webs, energy pyramids, and biogeochemical cycles?

Our Homeschool Co-op is doing a high school level class in Biology this year. Our main textbook is Holt Biology. The sections on this page accompany chapter 16: Ecosystems in Holt Biology. Whether you're in our homeschool co-op or not, you're welcome to follow along as we explore and marvel at the world around us.

Holt Biology

Holt Biology: Student Edition 2006
Holt Biology: Student Edition 2006
This book is available in both hardback and CD. Also, it's available new and used. Visit the link above to get the prices of different formats.

What is Ecology?

Definition of Ecology

Ecology is the study of how living organisms interact with one another and with their environment. Ecology helps us understand the connections between various living organisms and their environment. Ecology also helps us learn about ecosystems and about environmental problems and how we can best protect earth's resources for future generations.

What Is An Ecosystem?

Definition of an Ecosystem

An ecosystem consists of all the living and non-living parts of an area.

Examples of ecosystems include:

  • lakes (and all the living and non-living things in a lake)
  • forests (animals, plants, microorganisms, and the non-living physical components of a forest)
  • coral reefs,
  • rainforests,
  • a living tree or a rotting log,
  • deserts
  • a park
  • a field,
  • even a city.

Ecosystems: The Biosphere

In this video, Mr. Paul Anderson teaches us about the levels of organization within ecology (from largest to smallest):







He also teaches about abiotic and biotic factors, aquatic and terrestrial biomes, and factors that affect climate.

More Ecosystems Vocabulary

There is a lot of vocabulary in this section. Making and using flashcards of the vocabulary may help.

  • Ecology - the study of how living organisms interact with one another and with their physical environment.
  • Habitat - the home to a particular population of a species
  • Community - The species that live together in one habitat
  • Ecosystem - The community and the physical environment (soil, weather, water, etc.)
  • Abiotic Factors - the physical components of a habitat. The non living parts of the environment. (rocks, minerals, water, wind, weather, etc.)
  • Biotic Factors - Living things. Organisms.
  • Biodiversity - This includes all the variety of organisms, their genes, and their communities and ecosystems in a particular region.
  • Pioneer species - The first organisms to live in a new habitat, such as a new island formed by an underwater volcano. These are usually small and fast-growing plants. They help prepare the ground for later species.
  • Succession - the progression of species, beginning with the pioneer species (that begin growing when the habitat is new) and moving on to other species (as the habitat ages some). The first species pave the way for later species to follow by helping to create or enrich the soil. In succession, one species replaces another as the new species grows taller and blocks out the sun.
  • Primary Succession - Primary succession takes place in a brand new habitat (such as a new island formed by an erupting volcano), where no life has been living.
  • Secondary Succession - Secondary succession takes places in areas that have had previous growth and already have soil. If a fire burns a forest, secondary succession will take place and gradually rebuild the area into a forest.

Primary vs Secondary Succession

Other Important Information About Ecosystems

  • Everything is connected. When something happens to one part of an ecosystem, it affects other aspects of the ecosystems as well.
  • Ecosystems can be any size, from a rotting log or puddle on the ground, to an ocean. A scientist will decide on the size of the ecosystem that he/she wants to study, based on what he/she is researching.
  • Ecosystems can change over time. For example, if fire rips through a forest, the forest may become an empty field for a while. Gradually seeds will be blown there by the wind, or dropped there by birds passing over, and small plants will start to grow again. Gradually, other plants will begin to go there, eventually replacing the original plants, only to be replaced themselves by yet other plants. Of course, as the type of plants growing there changes, so do the types of animals living there.

Ecological Succession

Energy Flow In Ecosystems

Energy Flow In Ecosystems

A food chain

A food chain
A food chain | Source

A Food Chain and an Energy Pyramid

In the food chain above, Osprey eat northern pike, which eat perch which feed on bleak which feast on freshwater shrimp.

The same information can be represented in an energy pyramid, with the additional info of numbers.

Energy Pyramid

Energy Pyramid
Energy Pyramid | Source

Energy Flow in Ecosystems Vocabulary

  • Primary Productivity - the rate at which photosynthetic organisms can produce food from photosynthesis. This rate determines the amount of available energy in an ecosystem.
  • Food chain - the path of energy from the sun to producers to consumers to larger consumers, etc.
  • Tropic level- The various levels in a food chain. (The producers, the consumers, the consumers that eat those consumers, and so on)
  • Producers are organisms such as plants, algae, and bacteria, that get energy directly from the sun. This is the first trophic level.
  • Herbivores - This is the second tropic level. These are animals that eat plants.
  • Consumers are organisms that eat plants or other living things in order to gain energy. Both herbivores and carnivores are consumers.
  • Carnivores - Animals that eat other animals. This is the 3rd trophic level.
  • Omnivores - Are animals that eat both plants and animals.
  • Detritivores - Worms and decomposers who get their energy from eating wastes and dead animals.
  • Decomposers - Bacteria and fungi decompose things that were once living. This helps release nutrients back into the environment.
  • Food Web - An interconnected group of food chains.
  • Energy Pyramid - An Energy pyramid is a diagram that shows how energy flows through ecosystems. The lowest trophic level (producers) is on the bottom of the pyramid. Above that are the consumers that eat the producers. About that are the consumers that eat those consumers, and so on.)
  • Biomass - This is how biologists measure the amount of energy that is in the trophic levels. It's the dry weight of tissue and other organic matter.

Here's a simple food chain.

Simple Food Chain
Simple Food Chain | Source

Producers, such as plants, get their energy from the sun through photosynthesis. The sun's energy is then passed into the herbivores (animals that eat plants) as well as into the decomposers that decompose the plants. Carnivores (animals that eat other animals) get their energy from the herbivores. Decomposers get their energy from the produces, herbivores, and carnivores. In exchange, decomposers put nutrients into the soil. These nutrients are used by plants.

More Information About Energy Flow.

All energy comes originally from the sun. Plants capture that energy. Herbivores and omnivores that eat the plants get some of that energy. Organisms that eat those animals get energy from them. In this way, energy that originally came from the sun is passed on along the food chain.

As energy is passed from one organism to another, some energy is given off into the environment as heat. Therefore, the amount of usable energy decreases as the energy passes through the ecosystem. Only about 10% of the energy in one organism gets stored in the body of the next organism. For this reason, there is a limit to the number of trophic levels that an ecosystem can support. Most land ecosystems have only 3, or sometimes 4, trophic levels.

A Food Web is several interlocking and interdependent food chains put together

Waterbird Food Web
Waterbird Food Web | Source

Trophic levels

An organism's trophic level is the position it has in a food chain. A food chain shows how energy is passed along from the sun to one organism to another to another. The trophic level shows the number of steps away from the start of the food chain an organism is.

Trophic level 1 is the primary producers - organisms that can make their own food. Herbivores that eat those plants make up trophic level 2. Predators that eat the herbivores make up trophic level 3. Carnivores are at level 4 or 5.

First trophic level: Plants, Algae, Phytoplankton

First trophic level
First trophic level | Source

Second Trophic Level: Animals that eat plants

Second Trophic Level
Second Trophic Level | Source

Third Trophic Level: Foxes eat rabbits.

Third Trophic Level
Third Trophic Level | Source

Fourth Trophic Level: Eagles eat foxes

Fourth Trophic Level
Fourth Trophic Level | Source

Decomposers eat dead matter

Decomposers | Source


The plants, algae, and phytoplankton are primary producers. They get their energy from the sun through the process of photosythesis. Plants are at the first trophic level.


Rabbits eat plants and are at the second trophic level. Rabbits are primary consumers because they are the first level of consumers (animals) on a food chain.


Foxes eat rabbits (and other small animals). Foxes are at the second trophic level. Foxes are secondary consumers, because they eat other animals.

Golden Eagles

Golden Eagles eat foxes (and other small animals). Golden Eagles are at the third trophic level. They are at the tertiary consumer level.


Decomposers are organisms that eat dead things, including the producers, herbivores, and consumers. The act of decomposing puts nutrients back into the soil or land. The nutrients are later taken up by plants and are used along with the sun to make food for the plant.

Biogeochemical Cycles:

Cycling of Materials in Ecosystems. The Carbon Cycle, The Nitrogen Cycle, The Phosphorus Cycle, The Water Cycle

Cycling of Materials in Ecosystems: The Carbon Cycle, The Nitrogen Cycle, The Phosphorus Cycle

6.3 in Holt Biology

The nutrients of carbon, water, nitrogen, and phosphorus are never lost. They are simply recycled and used again.

We don't gain or lose molecules of water. We keep the same amount of water in our biosphere (the earth and it's atmosphere). It's the same with nitrogen, carbon, and phosphorus. The nutrients aren't used up; they're simply recycled over and over.

The Water Cycle

The Water Cycle
The Water Cycle | Source

The Nitrogen Cycle

The Nitrogen Cycle
The Nitrogen Cycle | Source

The Carbon Cycle

The Carbon Cycle
The Carbon Cycle | Source

Here's an image and description of The Phosphorus Cycle.

Below you'll find a video on the Carbon Cycle, the Nitrogen Cycle, the Water Cycle, and the Phosphorus Cycle.

Biogeochemical Cycles:

The Carbon Cycle, The Nitrogen Cycle, the Water Cycle, and the Phosphorus Cycle

- How nutrients are recycled through Earth and it's atmosphere, through living and non-living things.

If you find the first part of this video difficult to understand, don't worry! Keep watching - or move to 4:28 in the video and watch from that point on.

Cycling of Materials In Ecosystems Vocabulary

Four substances are very important in maintaining ecosystems: carbon, nitrogen, phosphorus, and water. All living organisms require carbon, nitrogen, phosphorus, and water, as well as hydrogen and sulfur, in large quantities. Water, carbon, nitrogen, and phosphorus pass from non living things to living organisms and then back into the environment again.

  • Biogeochemical Cycle - Biogeochemical cycles are the pathways that various substances take through the environment. For example, we have the water cycle, the carbon cycle, the phosphorus cycle and the nitrogen cycle.
  • Ground Water - This is water in the ground.
  • Water Cycle - You're probably familiar with the evaporation and condensation part of the water cycle already, but did you know that plants are part of the water cycle as well? Water is taken up from the ground into the roots of plants. Later that water evaporates (from the leaves) back into the environment.
  • Transpiration - is the process in which water evaporates from the leaves of plants.
  • Carbon Cycle- Carbon dioxide (from the air or water) is used by plants during photosynthesis. That carbon dioxide is later recycled back into the environment in one of three ways.

    a. Cellular Respiration - This is the process almost all living organisms use to turn food into useable energy. In the process, carbon dioxide is given off as a waste product.

    b. Combustion - Combustion means burning. As fossil fuels (coal, oil, and natural gas) are burned, they release carbon into the environment.

    c. Erosion - As sea shells turn into limestone, and the limestone erodes, the carbon that was in the shells is returned to the environment.

  • Phosphorus Cycle - Phosphorus is used by living thing in ATP (like a rechargeable battery in living organisms) and DNA. Soil and rocks contain phosphorus which gets passed on into water. This phosphorus conatining water gets taken up by the roots of plants, and is later passed on to the animals that eat those plants, and then to the animals that eat animals that ate plants.
  • Nitrogen Cycle- There are four main stages in the Nitrogen Cycle.

    a. Assimilation - is the process in which plants absorb and use nitrogen in making organic compounds.

    b. Ammonification - As plants and animals die and begin to decay, bacteria create ammonia. Ammonia has nitrogen in it. This process is called Nitrogen fixation

    c. Nitrification - is the process of making nitrate from ammonia.

    d. Denitrification - Is the process of changing nitrate into nitrogen gas.

Biological Communities - Symbiosis, Niches, and Biomes

You'll Find The Next Page In This Biology Series Here - Biological Communities - Symbiosis, Niches, and Biomes

Temperate Evergreen Forest Biome
Temperate Evergreen Forest Biome | Source

© 2011 JanieceTobey

Ecosystems and Ecology Guestbook - Comments? Questions?

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    • profile image


      9 years ago

      Great read, thanks for putting all this together!

    • profile image


      9 years ago

      It is so important to understand and respect what we have (while we still have it)

    • BuddyBink profile image


      9 years ago

      This is great. It is important to understand how one thing can affect other things in an ecosystem. An excellent educational lens. Thanks

    • Barb McCoy profile image

      Barb McCoy 

      9 years ago

      I love this lens...thorough and yet beautiful too. Great choice of videos. Thanks for pulling this together and I will be referring to in my OHC. :) Blessed.

    • profile image


      9 years ago

      Another work of excellence in education and beautifully done to engage every'll have them coming back for more!

    • ajgodinho profile image

      Anthony Godinho 

      9 years ago from Ontario, Canada

      Another great addition to your biology series. Ecosystems are indeed complex and I find them fascinating, even with my limited knowledge of the subject.

    • profile image

      TheLastResort LM 

      9 years ago

      Great information - I hope as many people as possible learn about the fragility of ecosystems, so that in the future we will be better able to protect our natural resources.

    • Timewarp profile image


      9 years ago from Montreal

      Quality lens with good info, blessed!

    • aesta1 profile image

      Mary Norton 

      9 years ago from Ontario, Canada

      This is really a good refresher with additional new ideas. Am learning.

    • emmaklarkins profile image


      9 years ago

      Looks like I need to go back to school. There's a ton of stuff here I didn't know!

    • annieangel1 profile image


      9 years ago from Yorkshire, England

      great lens! chock full of interesting information, well done.

    • profile image


      9 years ago

      Wonderfully laid out and chock-full of great info! Good work!


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