Chapter 3 Elissa oconnor

Case Study-

The case study focuses on how all of the different components of an ecosystem are related. It gives the example of a forest in Haiti and how all of the forest's biotic and abiotic components interacted and depended on each other.

What is an Ecosystem?

An ecosystem is a specific location on Earth containing interacting biotic and abiotic components. Components such as location, climate, and organisms that live and can survive in that specific area all impact what types of ecosystems occur in different areas. Ecosystems can be extremely large, or as small as a hole in a tree or the space underneath a rock.


There are different types of boundaries, those that are well-defined, and those that are subjective and not well-defined. Well-defined boundaries have characteristics such as identifiable biotic components (animals, microorganisms, etc.), as well as distinctive abiotic components (temperature, salinity, etc.).

  • Examples of well-defined ecosystem boundaries: caves, lakes, ponds
  • Subjective ecosystem boundaries: most terrestrial ecosystems are subjective and their boundaries are not clearly defined because of wide open spaces and free roaming animals, such as large fields or the area in between two mountain ranges
  • Photosynthesis and cellular respiration are examples of processes that are not bound to ecosystem boundaries, they are ways of transferring energy throughout organisms in different ecosystems, therefore not bound to any ecosystem boundary.

Energy flow through ecosystems

Autotrophs are organisms that use energy from the sun to produce usable forms of energy. Some examples of autotrophs include plants, algae, and some forms of bacteria.

  • Photosynthesis is the process by which producers (autotrophs) use solar energy to convert carbon dioxide and water into glucose.
  • Solar energy+6H2O+6CO2 => C6H12O6+6O2
  • Cellular Respiration is the process by which cells unlock the energy of chemical compounds
  • Respiration is performed by all organisms, including producers, whether by anaerobic respiration or aerobic respiration (without or with oxygen, respectively)
  • Energy+6H2O+6CO2 <= C6H12O6+6O2

Primary Consumers are consumers that eat producers. Also called herbivores. Examples include zebras, grasshoppers, tadpoles, and zooplankton.

Secondary Consumers are carnivores that eat primary consumers. Examples include lions, hawks, and rattlesnakes.

Tertiary Consumers are carnivores that eat secondary consumers. One example of a tertiary consumer is a bald eagle.

Consumers- Also known as heterotrophs, organisms which are incapable of photosynthesis and therefore incapable of producing their own energy, they must obtain their energy by consuming other organisms.

Producers- Also known as autotrophs, organisms that use solar energy in order to produce usable forms of energy. Producers are plants, algae, and bacteria

Scavengers- An organism that consumes dead animals. One example of a scavenger is a vulture.

Detritivores- An organism that specializes in breaking down dead tissues and waste products into smaller particles. One example of this is a dung beetle.

Decomposers- Fungi and bacteria that convert organic matter into small elements and molecules that can be recycled back into the ecosystem.

- Without scavengers, detritivores, and decomposers, there would be no way of recycling organic matter and the world would be full of dead animals.

Food Web


There are two types of primary productivity- Gross and Net

Gross Primary Productivity (GPP)- The total amount of solar energy that producers in an ecosystem capture via photosynthesis over a given amount of time.

Net Primary Productivity (NPP)- The energy captured by producers in an ecosystem minus the energy producers respire.

Net Primary Productivity = Gross Primary Productivity - respiration by producers

- Net primary productivity is the energy left over after the respiration from producers takes place, and gross primary productivity is the total amount of energy altogether.

Calculating GPP and NPP-

The NPP of ecosystems ranges from 25 to 50 percent of GPP. Of the one percent (on average) of the sun's energy captured by producers, about 60 percent of that is used to fuel the producer's respiration, and the remaining 40 is used to support the producers growth and reproduction.

Some ecosystems are more productive than others. The amount of energy available in an ecosystem determines how much life the ecosystem can support. For example, the amount of sunlight that reaches a lake surface determines how much algae can live in the lake. In turn, the amount of algae determines the number of zooplankton that the lake can support, and the size of the zooplankton population determines how many fish the lake can support. Therefore, the more energy and consuming is happening in an ecosystem, the more productive it will be.

Ecological efficiency- The proportion of consumed energy that can be passed from one trophic level to another.

Most ecosystems in nature operate at about 10 percent efficiency, however ranging anywhere from 5 to 20 percent.


Biogeochemical- relating to the cycle in which chemical elements and simple substances are transferred between living systems and the environment.

To keep track of the movement of matter in biogeochemical cycles, we refer to the components that contain the matter- including air, water, and organisms, as "pools." Processes that move matter between pools are known as "flows."

  • Hydrological Cycle- Heat from the sun causes evaporation from oceans, lakes, and soils. Energy from the sun also causes plants to perform transpiration, a process by which plants release water from their leaves into the atmosphere. The water vapor enters the atmosphere where it forms clouds and eventually falls back down as precipitation in the for of rain, snow, or hail. The precipitation either falls into the ocean or falls on land. The water that falls on land can either move as runoff and return to the ocean through land and streams, or evapotranspiration can take place, which is when water moves through an ecosystem through a combination of transpiration and evaporation. As water gets back to the ocean, it begins to evaporate again, which restarts the cycle. **Phosphorus gets released into the water on the ground, making the hydrological and phosphorus cycles converge**
  • Human impacts on the hydrological cycle- harvesting trees in a forest can reduce evapotranspiration, paving over land to build roads, businesses, and homes reduces the amount of percolation that can take place in a given area
  • Carbon Cycle- Producers take up carbon from the atmosphere by photosynthesis and pass it on to consumers and decomposers. Some inorganic carbon sediments out of the water to form sedimentary rock while some organic carbon may be buried and become fossil fuels. Respiration by organisms returns carbon to the atmosphere and water. Combustion of fossil fuels and other organic matter returns carbon to the atmosphere. ***Carbon being returned to water through respiration by organisms ties this cycle to the hydrological cycle.**
  • Human impacts on the carbon cycle- combustion of fossil fuels releases fossilized carbon into the atmosphere, which increases carbon concentrations in the atmosphere, tree harvesting increases levels of CO2 in the atmosphere
  • Nitrogen Cycle- The nitrogen cycle moves nitrogen around the biosphere. First is nitrogen fixation, where some organisms can convert nitrogen gas into ammonia. Then nitrification, which is the conversion of ammonia into nitrite and then into nitrate. Once producers take up nitrogen in the form of ammonia, ammonium, nitrite, or nitrate, they incorporate that element into their system using a process called assimilation. Then mineralization occurs, where fungal and bacterial decomposers break down the organic matter found in dead bodies and waste products and convert it into inorganic compounds. **Decomposers break down the organic matter to inorganic matter in both the nitrogen and phosphorus cycles**
  • Human impacts on the nitrogen cycle- fertilization of soils can lead to an excessive amount of nitrogen in one area, and also increased amounts of nitrogen in the atmosphere in regions where these fertilizers are used
  • Phosphorus cycle- Primarily operates between land and water, there is no gas phase. The phosphorus cycle 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 be taken in and used by producers through assimilation, and from these producers it moves through the food web. Once the organisms containing the phosphorus die, they are decomposed by fungi and bacteria which results in mineralization of the organic phosphorus back into inorganic phosphorus. In water, phosphorus can precipitate out of solution and form sediments, which over time are transformed into new phosphate rocks. **Relation to the nitrogen cycle- both cycles include assimilation and mineralization!**
  • Human effects on the phosphorus cycle- mining phosphate sediments used in the cycle from mountains to produce fertilizer, algal bloom is a result of human alterations to the phosphorus cycle.
  • Algal Bloom- a rapid increase in the algal population of a waterway
Raindrops=precipitation! Hydrological cycle!


Disturbance- Relating to an ecosystem, a disturbance is an event, caused by physical, chemical, or biological agents, resulting in changes in population size or community composition

Watershed- All land in a given landscape that drains into a particular stream, river, lake, or wetland. Watersheds play a large role in studying the environment because these are the locations where studies on biogeochemical cycles and disturbances are conducted.

Resistance is a measure of how much a disturbance can affect flows of energy and matter in an ecosystem

Resilience is the rate at which an ecosystem returns to its original state after a disturbance

So... resistance is measuring how much the disturbance affects the area and resilience is how long it takes to recover from a disturbance.

Restoration Ecology- The study and implementation of restoring damaged ecosystems. It is important because helps scientists work on restoration projects to restore water flows and nutrient inputs that are closer to historic levels so that the functions of these ecosystems can be restored, and also because it helps scientists work to reverse anthropogenic effects and restore the original function of that ecosystem.

Examples of restoration ecology- Two projects are currently occurring in the Florida Everglades and also in the Chesapeake Bay to restore water flows and nutrient inputs.

Intermediate Disturbance Hypothesis- This hypothesis states that ecosystems experiencing intermediate levels of disturbances are more diverse than those with higher or lower disturbance levels. This is because ecosystems with low disturbances experience competition among species, and natural selection takes over and then there are not as many species in this area. Also, in places where disturbances are frequent, population growth rates must be high enough to counter the effects that the disturbances have on the ecosystem so that the species can survive. So, intermediate disturbance levels keep the ecosystem more balanced out and therefore those are the ecosystems that are more diverse.

Values and Human Dependence on Ecosystems

Instrumental Value of an Ecosystem- A value that something has to many species including humans

Intrinsic Value of an Ecosystem- Value that the environment and life forms have in their own right, and which is not derived from the human use they can or cannot be put to.

Instrumental Values that can be beneficial to humans-

  • Provisions- Goods that are directly used by humans. Provisions have instrumental value because because humans need them, so we have set a value on them.
  • 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- Ecosystems that give humans support services that would be very expensive to create. Support systems provide value because they take away costs that without them would be needed from humans.
  • Resilience- The rate at which an ecosystem returns to its original state after a disturbance. This has instrumental value and provides value to humans because many disturbances are created by human activity. It also has value since ecosystems have resilience and can recover from disturbances rather than being overtaken by them.
  • Cultural Services- Ecosystems that help people by giving them benefits, such as cultural or aesthetic benefits. Cultural services have instrumental value because if an ecosystem becomes more important than solely the things within it, then it has moral value to humans.

Factors that impact the intrinsic value of an ecosystem are factors such as the organisms and species found in that ecosystem. Intrinsic value has to do with what those organisms and species represent on their own. Since intrinsic values are values that belong to other life forms independent of human influence, different types of factors and species living in an ecosystem would impact the intrinsic value, being that none of those things are being affected by humans.

Works Cited:

Friedland, Andrew, and Rick Relyea. "Chapter 2." Environmental Science for AP. 2nd ed. W.H. Freeman, 2015. 31-65. Print.

- pages 67-94


Created with images by PatricioHurtado - "conguillío national park volcano sky" • brainin - "roraima venezuela south america" • LoggaWiggler - "sunset abendstimmung lake" • technicolor76 - "water drops"

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