Compendium Review Chapter 23

I. The Nature of Ecosystems
II. Energy Flow
III. Global Biogeochemcial Cycles

I. The Nature of Ecosystems
A. Biosphere: Where organisms are found on planet Earth, from the atmosphere above to the depths of the oceans below, and everything in between.
B. Entire Biosphere is one giant Ecosystem: A place where organisms interact among themselves and with the physical and chemical environment.
- These interactions help maintain both the ecosystem and the biosphere.
- Human interactions can alter interactions between organisms and their environments in ways that reduce the abundance and diversity of life within the ecosystem.
C. Ecosystems: Many different types of terrestial ecosystems, also called biomes.
- Biomes: Temperature and rainfall define the biomes, whose organisms are adapted to the regional climate.
- Examples: Tropical rain forest, savanna, temperate grasslands, temperate forests, deserts, taiga, and tundra.
(Insert Terrestrial Biomes picture / ecology.botany.ufl.edu / http://ecology.botany.ufl.edu/ecologyf02/biodiv.html )
- Aquatic ecosystems: Divided by whether they are freshwater or salt water.
D. Biotic Components of an Ecosystem:
1d. Abiotic components: nonliving.
2d. Biotic components: living things categorized according to the food source.
- Autotrophs: Require only inorganic nutrients and an outside energy source to produce organic nutrients for their own use and for the other members of a community. They are called producers. (ie algae, photosynthetic organisms.)
- Heterotrophs: Need a source of organic nutrients. They are consumers.
* Herbivores: Animals that eat plants or algae. (ie insects, protists.)
* Carnivores: Feed on other animals. (ie birds that feed on insects, hawks feed on birds, etc.)
* Omnivores: Feed on both. (ie humans.)
* Detritus Feeders: Organisms that feed on detritus, which is decomposing particles of organic matter. (ie Earthworms, beetles, etc.)
E. Niche: Role of an organism in an ecosystem: how it eats its food and what eats it, and how it interacts with other populations in the same community.
F. Chemical Flow and Chemical Cycling
1f. Every ecosystem is characterized by two phenomena: energy flow and chemical cycling.
- Energy flow: Begins when producers absorb solar energy.
- Chemical Cycling: Begins when producers take in inorganic nutrients from the physical environment.
- Next, through photosynthesis, producers make organic nutrients directly for themselves and indirectly for the other populations of the ecosystem.
* Energy Flow: As nutrients pass from one population to another, all energy content is converted to heat, which dissipates in the environment.
- Most ecosystems require a constant supply of solar energy.
* Chemicals cycle when inorganic nutrients are returned to the producers from the atmosphere or soil. (Mader 493-495)
II. Energy Flow
A. Various interconnecting paths of energy flow are represented by a food web, which is a diagram that describes trophic (feeding) relationships.
- Two examples: Grazing Web- Begins with an oak tree and grass. Detrital Web- Begins with detritus and the decomposers found within detritus.
(Insert Grazing and Detritus Food Webs picture / project.bio.iastate.edu / http://project.bio.iastate.edu/Courses/biol123/lectures/Lecture06-Ecosystems/slide10.htm)
B. Trophic Levels:
1b. Food Chains: Diagrams that show a single path of energy flow. Ex. In grazing food chain, you would have leaves, followed by caterpillars, followed by birds, followed by hawks. In detrital food chain, you would have detritus, followed by earthworms, followed by shrews.
2b. Trophic level: Composed of all the organisms that feed at a particular link in a food chain. Example: In grazing food web, trees are producers (first trophic level), first series of animals are primary consumers (second trophic level), and the next group of animals are secondary consumers (third trophic level).
C. Ecological Pyramids: The flow of energy with large losses between successive trophic levels.
- Only about 10% of the energy of one trophic level is available to the next tropic level.
1c. Biomass: The number of organisms multiplied by the weight of organic matter within one organism. (Mader 497-498)
III. Global Biogeochemical Cycles
A. All organisms require a variety of organic and / or inorganic nutrients.
1a. Biogeochemical Cycles: Pathways by which chemicals circulate through ecosystems involve both living (biotic) and nonliving (geological) components.
- Gaseous: Element returns to and is withdrawn from the atmosphere as a gas. (ie carbon and nitrogen cycles.)
- Sedimentary: The chemical is absorbed from the soil by plant roots, passed to heterotrophs, and returned to soil by decomposers. (ie phosphorus cycle.)
2a. Chemical Cycling involves a reservoir, an exchange pool, and a biotic community.
- Human activities remove chemicals from reservoirs and exchange pools, and make them available to the biotic community. Can result in pollution, because it upsets the normal balance of nutrients for producers in the environment.
B. The Water Cycle:
1b. Evaporation, precipitation, runoff, etc. See picture. All water is eventually returned to the sea. Aquifer: Rock layers that contain water and release it.
(Insert Water Cycle picture / Frolich PowerPoint Slide 18)
2b. Human Activities:
-Humans interfere w/ water cycle in three ways: First, they take water from aquifers. Second, They clear vegetation from land and build roads and buildings that prevent percolation and increase runoff. Third, they interfere with the natural processes that purify water and instead add pollutants like sewage and chemicals to water.
C. The Carbon Cycle:
1c. Carbon dioxide in atmosphere is the exchange pool for the carbon cycle.
- In this cycle, organisms in both terrestrial and aquatic ecosystems exchange carbon dioxide with the atmosphere. ie. Plants take co2 from air, and through photosynthesis, incorporate carbon into nutrients that are used by autotrophs and heterotrophs. When organisms respire, carbon is returned to the atmosphere as co2. In aquatic, it is indirect: co2 from air combines with h2o to produce bicarbonate ion, a source of carbon for algae that makes food for themselves and for heterotrophs. When aquatic organisms respire, the co2 they give off becomes bicarbonate ion.
2c. Living and dead organisms contain organic carbon and serve as one of the reservoirs for the carbon cycle. Decomposition returns co2 to the atmosphere.
3c. Fossil Fuels: When plant and animal remains are transformed into coal, oil, and natural gas.
4c. Human Activities:
- More co2 is being deposited in the atmosphere than is being removed. Largely due to burning of fossil fuels and destruction of forest. When a forest is destroyed, we reduce a reservoir and the very organisms that take up excess co2.
5c. Global Warming: Human activities emit co2 and other gases, like nitrous oxide into the atmosphere. These gases are known as greenhouse gases, because they allow solar radiation to pass through but hinder the escape of infrared rays back into space.
- Contribute to rise in Earth's ambient temperature, = global warming.
- Higher temperature = greater evaporation of h2o, forming more clouds, and setting up a positive feedback effect that will increase global warming even more.
- Other effects: Temps in polar regions rise, glaciers will melt, sea levels will rise, h2o evap. will increase, = increased rainfall along coasts and dryer conditions inland. Droughts reduce agricultural yields, trees will die, etc. Coastal cities could sink! (Mader 498-499)
(Insert Greenhouse Effect picture / Frolich PowerPoint Slide 21)
D. The Nitrogen Cycle: Nitrogen gas accounts for approx. 78% of the atmosphere.
1d. Ammonium Formation and Use:
- Nitrogen fixation occurs when nitrogen gas is converted to ammonium, a form plants can use.
2d. Nitrate Formation and Use:
- Plants can use nitrates as a source of nitrogen.
- Nitrification: Production of nitrates during the nitrogen cycle. Can occur when cosmic radiation, meteor trails, and lightning provide high energy needed for nitrogen to react with oxygen. Or, when ammonium in the soil is converted to nitrate by soil bacteria, or when nitrate-producing bacteria converts nitrite to nitrate.
- Assimilation: Plants take up ammonia and nitrate from the sol and use these ions to produce proteins and nucleic acids.
(Insert Nitrogen Cycle picture / www.stormfront.org / http://www.stormfront.org/forum/showthread.php?t=325972)
3d. Formation of Nitrogen Gas from Nitrate:
- Denitrification: The conversion of nitrate back to nitrogen gas, which enters the atmosphere. Counterbalances nitrogen fixatin except for human activities.
4d. Human Activities: Significantly alter the transfer rates in the nitrogen cycle by producing fertilizers from nitrogen- nearly doubles the fixation rate. Runs off into water, creates overgrowth of algae, causes over-enrichment, and when algae die off, increased decomposer populations use up all oxygen in water, and results in massive fish kill.
1e. Acid Deposition: Nitrogen oxides and sulfur dioxide enter atmosphere from burning of fossil fuels. These gases combine with water vapor to form acids that return to the earth, and their deposit affects forest and lakes.
- Creation of smog, and trapped pollutants.
E. The Phosphorus Cycle: Phosphorous trapped in oceanic sediments moves onto land after a geological upheaval. Weathering of rocks places phosphate ions into soil. Some of this phosphate is used by plants in a variety of molecules, and the nucleotides that become a part of DNA and RNA. Animals eat producers and incorporate some of the phosphate into teeth, bones, and shells, which take many years to decompose.
(Insert Phosphorous Cycle picture / www.biologycorner.com / http://www.biologycorner.com/bio4/notes/chap45.html )
1e. Phosphorus and Water Pollution:
- Cultural Eutrophication: Overenrichment of waterways due to humans use of phosphate for fertilizer, animal wastes from livestock feedlots, and discharge from sewage treatment plants.
- Biological Magnification: Occurs as materials pass along a food chain and become more and more concentrated because they remain in body and are not excreted.
- Pollutants: Waste dumping, offshore mining and shipping, oil spills, etc.
- Many species are at the brink of extinction. (Mader 500-505)