1. Organisms: Identify and analyze the functions of organisms within the population of the ecosystem

2. Roles of Organisms
The main concepts we are trying to get across in this section concern how energy moves through an ecosystem. If you can understand this, you are in good shape, because then you have an idea of how ecosystems are balanced, how they may be affected by human activities, and how pollutants will move through an ecosystem.
Organisms can be either producers or consumers in terms of energy flow through an ecosystem.

3. Producers
Producers convert energy from the environment into carbon bonds, such as those found in the sugar glucose.
Plants are the most obvious examples of producers; plants take energy from sunlight and use it to convert carbon dioxide into glucose (or other sugars).
Algae and cyanobacteria are also photosynthetic producers, like plants.
Other producers include bacteria living around deep-sea vents. These bacteria take energy from chemicals coming from the Earth's interior and use it to make sugars. Other bacteria living deep underground can also produce sugars from such inorganic sources.
Another word for producers is autotrophs.

4. Consumers
Consumers get their energy from the carbon bonds made by the producers.
Another word for a consumer is a heterotroph.
Based on what they eat, we can distinguish between 4 types of consumers or heterotrophs:
Consumer Trophic level Food source
Herbivores primary plants
Carnivores secondary or higher animals
Omnivores all levels plants & animals
Detritivores detritus

5. A trophic level refers to the organisms position in the food chain
A trophic level refers to the organisms position in the food chain. Autotrophs (Producers) are at the base.
Organisms that eat autotrophs (Producers) are called herbivores or primary consumers.
An organism that eats herbivores is a carnivore and a secondary consumer.
A carnivore which eats a carnivore which eats a herbivore is a tertiary consumer, and so on.
It is important to note that many animals do not specialize in their diets.
Omnivores (such as humans) eat both animals and plants.
Further, except for some specialists, most carnivores don't limit their diet to organisms of only one trophic level. Frogs, for instance, don't discriminate between herbivorous and carnivorous bugs in their diet. If it's the right size, and moving at the right distance, chances are the frog will eat it. It's not as if the frog has brain cells to waste wondering if it's going to mess up the food chain by being a secondary consumer one minute and a quaternary consumer the next.

6. Energy Flow Through the Ecosystem
A few generalizations from the above diagram:
The ultimate source of energy (for most ecosystems) is the sun.
The ultimate fate of energy in ecosystems is for it to be lost as heat.
Energy and nutrients are passed from organism to organism through the food chain as one organism eats another.
Decomposers remove the last energy from the remains of organisms.
Inorganic nutrients are cycled, energy is not.

7. Food Chain What is for dinner?
A food chain is the sequence of who eats whom in a biological community (an ecosystem) to obtain nutrition.
A food chain is how energy is passed, in the form of food, from one organism to another.
Examples:
algae--- > copepod--- > fish--- >squid--- >seal--- >orca
grass ---> grasshopper --> mouse ---> snake ---> hawk
Food chain is the path of food from a given final consumer back to a producer.
A food chain starts with the primary energy source, usually the sun or boiling-hot deep sea vents.
The organisms in the food chain are
Producers,
Consumers, and/or
Decomposers.
Some organisms make their own food (producers), while others need to eat other organisms for food (decomposers and consumers).
A food chain is one single path, but in the real world there is not a straight path, but rather a web of paths. This is because many animals do not consume only one type of plant or animal.
A food web is made up of interlocking food chains.

8. Terms
A food chain is how energy is passed, in the form of food, from one organism to another.
The organisms in the food chain are
Producers,
Consumers, or
Decomposers.
Some organisms make their own food (producers), while others need to eat other organisms for food (decomposers and consumers).
A food chain is the path of food given from the final consumer back to a producer.
A food chain is one single path, but in the real world there is not a straight path, but rather a web of paths. This is because many animals do not consume only one type of plant or animal.
A food web is made up of interlocking food chains.

10. Some Facts
Water and energy are vital to the survival of an ecosystem, conservation is needed.
Most ecosystems conserve the resources naturally.
An example would be the exchange of carbon dioxide (given off from animals) and oxygen (given off by plants).
Another example is the waste of some species becomes the food of another.
When there are limited resources, the conservation process is urgent and more visible.
If the conservation efforts do not succeed, then species can become endangered or even extinct.
Species become endangered with the available habitat can no longer support the members of a population.
When a habitat disappears and all of the members of a population die, the species is considered extinct.

11. Example of a Food Chain

12. Food Web A food web is made up of interlocking food chains
While many organisms do specialize in their diets, other organisms do not. Hawks don't limit their diets to snakes, snakes eat things other than mice, mice eat grass as well as grasshoppers, and so on.
A more realistic depiction of who eats whom is called a food web; an example is shown below:
We can now see that a food web consists of interlocking food chains, and that the only way to untangle the chains is to trace back along a given food chain to its source.

13. Example of Food Web