APES Chapter 3 ecosystem ecology


Case Study-The case study found in module 6 highlights the idea that all components of an ecosystem are interrelated. It did so specifically by providing an example of the forest in Haiti and how all of it's components, both living and nonliving, interacted and were dependent on one another.

3.1 : Components of an Ecosytem

-Ecosystems are defined as a biological community of interacting organisms and their physical environment. In other words, all of the living and nonliving things living in an area. Living, or biotic, factors include plants, animals, and bacteria, while nonliving, or abiotic, factors include air, water, and other natural compounds found in the environment such as nitrogen and carbon.

-Many components impact what types ecosystems occur in an area. Some of these components include temperature, precipitation, and variations in soils. These things will dictate the conditions of an area and which species can survive there. Then based on the species that inhabit the area, we can classify the ecosystem.

-The biotic and abiotic components of an ecosystem provide the boundaries that distinguish one ecosystem from another. Some are very well-defined, such as that of a cave. It contains very identifiable species that are specifically adapted to live in that area. This concept is similar in other areas such as lakes and ponds, as they contain clear boundaries. However other ecosystems are not as clear cut. They are then defined by things such as the range of a particular species of interest, geographical features, or even sometimes administrative boundaries, which are those created by people rather than being based on scientific criteria.

-Some processes that are not bound to ecosystem boundaries include those that involve the movement of matter and energy. These, for example, are things such as photosynthesis and respiration. These processes take place over the entire earth and cycle matter and energy that is not contained to one ecosystem, but rather flows through many.

3.2 : Energy Flow in Ecosystems

-Organisms that use the energy of the sun to create usable forms of energy are known as autotrophs, or producers. These are things such as plants, algae, and some bacteria. To create their energy, they use a process called photosynthesis. The equation is shown below:

sunlight+ carbon dioxide+ water = oxygen+ energy

-Organisms who do not use photosynthesis such as animals that are herbivores and carnivores, must use a different method to create and utilize energy. This method is called cellular respiration. In this process cells unlock energy from chemical compounds. It can be completed both in the presence of oxygen, known as aerobic respiration, and in the absence of oxygen, known as anaerobic respiration. The respiration equation is shown below:

glucose+ oxygen= carbon dioxide+ water+ energy

Of the organisms that obtain energy through consuming others, there are three different trophic levels: primary consumers, secondary consumers, and tertiary consumers.

  • primary- consumers that eat producers; herbivores
  • secondary- a carnivore that eats primary consumers
  • tertiary- a carnivore that eats secondary consumers

However, there are also many other classifications of organisms besides the producers and consumers that have already been mentioned:

  • producer- an organism that uses the sun to produce usable forms of energy
  • consumer- an organism that is incapable of photosynthesis and must obtain its energy by consuming other organisms.
  • scavenger- an organism that consumes dead animals
  • detritivore- an organism that specializes in breaking down dead tissues and waste products into smaller particles
  • decomposers- fungi and bacteria that convert organic matter into small elements and molecules that can be recycled back into the ecosystem.


Gross primary productivity and net primary productivity are two calculations found in chapter 3.

  • GPP- the total amount of solar energy that producers in an ecosystem capture via photosynthesis over a given amount of time.
  • NPP- the energy captures by producers in an ecosystem minus the energy producers respire.

To calculate GPP, know that of all the sunlight hitting an area, 99% is either reflected or passes through producers without being absorbed. This leaves 1% that is absorbed by producers during photosynthesis.

To calculate NPP, know that 60% of the total 1% of sunlight (GPP) that was absorbed for photosynthesis, is lost to respiration. This leaves 40% of the total GPP that supports the growth and reproduction of producers, and is the NPP.

Productivity and Ecological Efficiency

Ecosystems that have plenty of sunlight, lots of available water and nutrients, and warm temperatures will be the most productive. This is because they provide the best conditions to support a large producer population, and a large producer population is what is needed to support all other species in an area. These extremely productive ecosystems include rainforests and salt marshes, while ecosystems such as tundras and deserts would be much less productive.

The NPP of an ecosystem establishes the rate at which biomass- the total mass of all living matter in an area- is produced over a given amount of time. The amount of biomass present in an ecosystem at a particular time is its standing crop. The more producers that are available, the higher the biomass, and therefore standing crop, of that area will be. This gives a measurement of the amount of energy available in an ecosystem. The proportion of consumed energy that can be passed from one trophic level to the next is referred to as ecological efficiency. So, a higher biomass creates a higher standing crop, which means there is more energy available in an ecosystem, which means more energy can be passed from one trophic level to another, creating a more ecologically efficient environment.

3.3 : Carbon, Nitrogen, and Phosphorus Cycles


Because the movement of matter within and between ecosystems involves cycles of biological, geological, and chemical processes, these cycles are known as biogeochemical cycles. To keep track of the movement of matter in these cycles, the places where the matter is contained are called pools and the processes that move the matter between pools are called flows.

Hydrologic Cycle: Water continually cycles from the earth's atmosphere to the surface. Heat from the sun causes water being stored in oceans, lakes, and soils to evaporate. This solar energy which is also responsible for photosynthesis causes plants to give off water as a product of the process, known as transpiration. Water from both of these sources enters the atmosphere and forms clouds, known as condensation. It returns to the earth through precipitation, whether it be rain, snow, or hail. Once back on the surface, it is either reabsorbed into the atmosphere, taken up by the roots of plants and released again after photosynthesis, absorbed by the soil into groundwater, or moves as runoff into streams and rivers. Some human effects on the hydrologic cycle include deforestation, which reduces transpiration, and also clear-cutting mountain slopes and paving land, both of which increase percolation of water in the ground and runoff.

Carbon Cycle: In the carbon cycle, producers take up carbon from the atmosphere via photosynthesis and pass it on to consumers and decomposers. Also, some inorganic sediments out of the water to form sedimentary rock, while some organic carbon may be buried and become fossil fuels. Meanwhile, carbon is constantly being released from the ocean and atmospheric carbon dioxide is constantly diffusing into the ocean, a process known as exchange. The amount of carbon being released and absorbed is roughly equal. Respiration by organisms also returns carbon to the atmosphere and water. Finally, combustion of fossil fuels and other organic matter returns carbon to the atmosphere. Human effects on the carbon cycle include extraction, which is the process of removing buried carbon, bringing it to the surface where is can be combusted. The sharp increase of human fossil fuel combustion over recent years has contributed very large amounts of carbon dioxide to the atmosphere. This carbon dioxide increases the heat retention of the atmosphere, resulting in global warming.

Nitrogen Cycle: The nitrogen cycle moves nitrogen from the atmosphere and into soils through several fixation pathways so that it can be used by producers. This can occur through abiotic processes such as combustion which creates nitrate, a form that is usable to plants. It can also occur through biotic processes such as fixation through bacteria, which convert the nitrogen gas into ammonia which can also be used by plants. The next step is nitrification, which converts ammonium to nitrite, then to nitrate. Once the producers take in the nitrogen in whatever fixed form, they incorporate it into their tissues in a process called assimilation. The producers are then consumed and nitrogen is passed to various other organisms. Eventually, when those organisms die, fungal and bacterial decomposers break down their bodies and organic compounds are returned to the soil to be fixed again, a process called mineralization. Human effects on the nitrogen cycle include the use of nitrogen fertilizers, which adds excess nitrogen to the atmosphere and water and can alter the distribution or abundance of species in an ecosystem.;:

Phosphorus Cycle: The phosphorus cycle is the only cycle that is not atmospheric. It begins with the weathering or mining of phosphate rocks and the use of phosphate fertilizer, which releases phosphorus into the soil and water. This phosphorus can then be used by producers, a process called assimilation, then subsequently moves through the food web to consumers. Once again, when organisms die, phosphorus is returned to the soil through mineralization. In water, phosphorus can precipitate out of a solution and form sediments, which over time are transformed into new phosphate rocks, restarting the cycle. Human effects on the phosphorus cycle include the use of fertilizers which add excess phosphorus into water bodies, causing a large increase in the growth of producers, known as algal blooms, which lower oxygen levels in the water.

3.4 : Natural and Anthropogenic Disturbances

A disturbance is defined as an event, caused by physical, chemical, or biological agents, resulting in changes in population size or community composition.

To understand how disturbances affect ecosystem processes, scientists often use watersheds. A watershed is all of the land in a given landscape that drains into a particular stream, river, lake, or wetland. With the use of watersheds, scientists can observe the effects of environmental disturbances without it having to be on a global scale.

When an ecosystem is faced with disturbance, its productivity is often affected. To measure the affects of these disturbances, scientists use resistance and resilience.

  • resistance- a measure of how much a disturbance can affect flows of energy and matter in an ecosystem.
  • resilience- the rate at which an ecosystem returns to its original state after a disturbance.

restoration ecology:

Restoration ecology is the study and implementation of restoring damaged ecosystems. Many environmental disturbances such as urbanization, clear-cutting, and draining of wetlands are so large that they can eliminate entire ecosystems. Restoration ecology has emerged as an action to restore damaged ecosystems and preserve their species. Current projects include the Florida Everglades and the Chesapeake Bay.

intermediate disturbance hypothesis:

The intermediate disturbance hypothesis states ecosystems experiencing intermediate levels of disturbance will favor a higher diversity than those with high or low disturbance levels. This is because a moderate amount of disturbances keep species from eventually dominating an ecosystem. It also keeps disturbance levels from becoming too high, and possibly causing the disappearance of certain species as a result. With an intermediate level, the highest level of diversity exists.

3.5 : Values of Ecosystems and How Humans Depend on them

When assigning a "value" to a species or ecosystem, there are two different classifications:

  • Instrumental- value that something has to other species, including humans
  • Intrinsic- value that something possesses as its own right, as an end-if-itself; in other words, value just because it exists.

Many instrumental values can provide value to humans. Some of them include:

  • Provisions- Provisions are goods that humans use directly. These obviously have instrumental value because they are needed by humans, we therefore have set a value on their existence
  • Regulating Services- Regulating services refer to natural ecosystems that help to regulate environmental conditions. These have instrumental value because they maintain the conditions in which we live, and are therefore serving a bigger purpose than just existing.
  • Support Systems-Support systems refer to natural ecosystems that provide numerous support services that would be extremely costly for humans to generate. This has clear instrumental value because they alleviate costs that would otherwise be needed by humans, therefore their existence has value to us.
  • Resilience- Resilience is defined as the rate at which an ecosystem returns to its original state after a disturbance. This has instrumental value and is valuable to humans because many disturbances are imposed by humans. So, because ecosystems are resilient and are able to bounce back rather than dying as a result of a disturbance, is valuable to us.
  • Cultural Services- Cultural services refer to ecosystems that provide cultural or aesthetic benefits to many people. This is instrumental value because a certain ecosystem becomes more important than just its components, and now has moral value to people.

Intrinsic value of an ecosystem is influenced by many different factors. For example, it can be determined by species that are found in that ecosystem. The intrinsic value of an object deals more with abstract ideas and concepts, such as what a species or ecosystem represents, what it embodies, its rarity, its beauty, or its history.


  1. Friedland, Andrew, and Rick Relyea. "Chapter 2." Environmental Science for AP. 2nd ed. W.H. Freeman, 2015. 67-99. Print.
  2. www.youtube.com
  3. http://www.nature.com/scitable/knowledge/library/intrinsic-value-ecology-and-conservation-25815400


Created with images by BLMOregon - "Views from Cascade-Siskiyou National Monument -- Pilot Rock" • AdinaVoicu - "sunset birds cloud" • cluczkow - "tree" • skeeze - "dallas texas skyline" • skeeze - "polar bears wildlife snow" • janeb13 - "blue whale ocean mammal" • laurentmarx - "elephant safari animal" • 3031830 - "cheetah wild africa"

Made with Adobe Slate

Make your words and images move.

Get Slate

Report Abuse

If you feel that this video content violates the Adobe Terms of Use, you may report this content by filling out this quick form.

To report a Copyright Violation, please follow Section 17 in the Terms of Use.