Ecosystem: All organisms living in a given area along with the abiotic factors with which they interact and involves energy flow and chemical cycling



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Bio 215 Chapter 49 Ecosystems:

Ch 49: Ecosystems:
Ecosystem: All organisms living in a given area along with the abiotic factors with which they interact and involves energy flow and chemical cycling

1. Trophic structure determines an ecosystems energy and chemical cycling


1) Each ecosystem has a trophic structure of feeding relationships that determine the paths of energy flow and chemical cycling
2)The five trophic levels include

a. Primary producers: autotrophs that support all other levels

b. Primary consumers: animals that consume the producers

c. Secondary consumers: carnivores that consume the primary consumers

d. Tertiary consumers: carnivores that eat other carnivores

e. Decomposers: animals that eat dead organisms

3) Food chain: Pathway along which food is transferred from trophic level to trophic level, is usually highly branched and resembles a web

A. Producers: usually plants

1. can be algae

2. aphotic zone of sea receives dead detritus from overhead

3. deep sea vents rely on chemical energy from bacteria

B. Consumers: vary with type of ecosystem

1. Terrestrial: insects, snails, grazing mammals, can be a few big animals or many small ones

2. aquatic: zooplankton, small invertebrates and some fish

3. all have their own predators

C. Decomposers (Detritivores)

1. are critical components of any ecosystem

2. link between primary produces and higher level consumers

3. mostly bacteria and fungi

4. earthworms are also important decomposers


2. Primary productivity and energy budget

1) Energy is needed for growth, maintenance and reproduction

2) energy is trapped from sunlight by primary producers, which then provide chemical energy in the form of ATP to the rest of the animals

A. The amount of solar radiation striking the earth's surface shows dramatic regional variation

1. Light energy is used to produce roughly 170 billion tons of organic material each year

B. Primary productivity: amount of light energy converted to chemical energy by autotrophs of an ecosystem

1) Net primary productivity (NPP)= GPP -Rs (energy used by producers for respiration

2) Primary productivity should not be confused with standing crop biomass



  • f. is the rate at which new biomass is synthesized by vegetation

  • g. standing crop may accumulate over time

  • h. productivity is due to the rate and size of an ecosystem.

(1) tropical forests have a high rate and cover a large area

(2) open oceans have a low rate but cover 7/10 of the earth

3) Factors important in limiting productivity

a) Typically precipitation, temperature and light intensity

(1) Limited by availability of inorganic nutrients

(2) limiting nutrient: limits the amount of growth in a biome

(a) typically nitrogen and phosphorus

b) aquatic ecosystems productivity determined by light intensity, water temp and availability of inorganic nutrients

(1) nitrogen and phosphorus are limiting in open water

(2) phytoplankton is post productive in regions of upwellings

(a) typically occur in polar areas

3. As energy flows through an ecosystem, each trophic level has losses

1. energy flow is very inefficient

A. Secondary productivity: is rate at which consumers convert the chemical energy in the food they eat into their own biomass

1. energy flows through a ecosystem, it does not cycle

2. carnivores are more energy efficient, but use a lot of energy in respiration

A. Ecological Efficiency and Ecological pyramids

1) Ecological efficiency: ration of net productivity at one trophic level compared to net productivity at the level below: the percentage of energy transferred from one trophic level to the next

a. efficiency is typically 5 to 20 percent 85 to 90% of the energy of a trophic level is lost

2) Ways to represent energy levels

b. pyramid of productivity: trophic levels stacked in blocks proportional to productivity

c. biomass pyramid: symbolizing dry weight of organisms

(3) can be inverted in aquatic systems due to fast growth

d. pyramid of numbers: blocks represent numbers of individuals


1) Matter cycles within and between ecosystems

1) Energy is constant form sunlight, but other essential chemical elements have to be continuously recycled. Decomposers play an important role here.

A. biogeochemical cycles: nutrient circuits involving both biotic and abiotic components of ecosystems

1. Carbon, oxygen, sulfur and nitrogen have gaseous forms and their cycles are global

2. phosphorus, potassium, calcium and trace elements are recycled locally

B. reservoirs: are defined by two characteristics: whether they contain organic or inorganic materials: and whether or not the materials are directly available for use by organisms

3. available organic reservoir: contains the living organism and detritus, available by feeding

4. Unavailable organic reservoir: composed of coal, oil and peat, is not eatable

5. available inorganic reservoir: all mater present in soil, air or dissolved in water

6. unavailable inorganic reservoir contains nutrients tied up in limestone and other rocks

C. Processes involved n transfer of nutrients between the four reservoirs and the basis for biogeochemical cycling

7. Weathering and erosion

8. burning of fossil fuels

9. fossilization

10. sedimentary rock formation

11. photosynthesis


5. The processes that drive chemical cycles

A. The water cycle



  1. contributes to the fitness of the environment

  2. most cycling occurs between the oceans and the atmosphere

a. solar energy evaporates water from the oceans

b. water vapor condenses and forms rain over land

3) The water cycle differs from other cycles in that it is a physical process

B. The Carbon Cycle

1. autotrophs fix carbon dioxide form the atmosphere during photosynthesis

2. carbon dioxide is released back into the atmosphere by respiration

3. the carbon cycle is very fast

4. Other carbon cycles are slow

a. carbon is diverted into wood or other durable organic material

b. can also be locked up in coal and oil deposits

5) The oceans may act as a buffer that do not allow the carbon dioxide amount in the atmosphere to vary widely

6) carbon dioxide is dissolved in water and is chemically converted to other forms. All told ocean contains 50 x the amount of carbon as is available in the atmosphere

C. The Nitrogen Cycle

c. Makes up amino acids and nucleic acids

d. 80% of earth atmosphere is gaseous nitrogen

e. biologically useful forms

(1) ammonium (NH4)

(2) nitrate (NO3)

1. Atmospheric deposition: 5 to 10% dissolved in rain or dust

2. Nitrogen fixation: reduction of atmospheric nitrogen to ammonia by organisms

3) Nitrification: metabolic process by which certain aerobic soil bacteria use ammonium (NH4+) as energy source by first oxidizing it to NO2- (nitrite) then to nitrate (NO3-), which plants can use

4) Denitrificaiton: process that returns nitrogen to the atmosphere by converting nitrate to nitrogen gas, used in the place of oxygen.

3. Ammonification: decomposition of organic nitrogen back into ammonia

4. Important aspects of nitrogen cycle

a. prokaryote serves as vital links at several points in the cycle

b. the nitrogen cycling involved nitrogenous compounds in soil and water

c. nitrogen fixation is only occurring in certain plants

d. denitrificaiton returns small amounts of nitrogen back into the atmosphere

e) most assimilated nitrogen comes form nitrate which is efficiently recycled form organic forms by ammonification and nitrification

e. the majority of nitrogen is recycled locally

D. The Phosphorus cycle

a. is a major component of nucleic acids, phospholipids, ATP and minerals in bones and teeth

b. is a simple cycle

1. Local phosphorus cycle

a. weather of rock adds phosphate to the soil

b. producers absorb the soil phosphate and incorporate into molecules

c. phosphorus is transferred to consumers in organic form

d. phosphorus is added back to the soil by secretion and decomposition of detritus

2. phosphorus cycle is localize since humus and soil particles bind phosphate

a. weathering of rocks keeps phosphorus constant

b. phosphorus is reincorporated into rocks in the ocean

3. Phosphorus may limit algal productivity in aquatic habitats

E. Variations in Nutrient-Cycling Time

1. Rate of decomposition has a great impact on the time table for nutrient cycling

a. decomposition is quicker in tropical areas that in temperate areas

2. In tropical rain forests levels are much lower than those found in temperate forests

a. much of the nutrients are held up in the biomass

3) Temperate soils contain 50% of ecosystem nutrients and are held for a long time before assimilation occurs

4) Sediments of aquatic systems for a nutrient sink and their must be an interchange between the bottom layers of water and the surface for the ecosystem to be productive.
6. Field experiments

A. Long term ecological research

1. by measuring the inflow and outflow of several valleys scientists were abet to determine that

a. 60^ of rainfall exits through steams and 40% is lost by transpiration

b. mineral loss was almost minimal

2. By logging the forest scientist observed

a. Water runoff increased by 40%

b. Many minerals were lost in runoff

B. The study demonstrated the importance of plants in retaining nutrients within an ecosystem and the effects of human intrusion into a system
7. Human population is disrupting chemical cycles throughout the biosphere

1) human population has intruded into the dynamics of most ecosystems through human activities or technology

a. some system have been totally destroyed

b. some effects like acid rain are global in nature

c) human activity often removed nutrients form one part of the biosphere and adds them to another

d) Farming exhausts the natural store of nutrients as crop biomass is removed form an area, this greatly reduces the amount of nutrients recycled, Supplements must then be added

(1) results in nutrients in sewage etc
B. Agricultural effects on Nutrient Cycling

1. More agriculture results in

a. Intrusion into the cycling of nutrients

b. over harvesting of natural populations of food species

c. introduction of toxic compounds into the ecosystems

2. Stability of farming depends on

a. how long the area can sustain crops after natural vegetation is removed

b. tropical farmland is poor in nutrients

c. temperate crops may last years

d. nutrients are typically added back with synthesized fertilizers

3. The nitrogen cycle of an area is greatly impacted by agriculture

a. breaking up soil increases decomposition

b. nitrates are leached out of system

c. fertilizers are applied to replace lost nitrogen

d. still more nitrogen is lost by leaching

C. Accelerated Eutrophication of lakes

1. lakes naturally go through a process of filling in, and nutrient acquirement

2. mankind will artificially speed this process up, can lead to overgrowth and the ruining of a lake

D. Poisons in Food chains

1. A variety of toxic substances are dumped into the food chain

a. many are not degraded by microbes and persist for years and decades

b. some are converted to toxic substances by microbial action

2. Toxins are acquired with foods

a. some are degraded

b. some are excreted

c) Biological magnification= toxins become more concentrated with each successive trophic level of a food web. results from biomass at each trophic level being produced from a much larger biomass ingested form the level below.

(1) DDT is biologically magnified

(2) used to control mosquitoes

(3) does not degrade easily

(4) is lipid soluble and accumulates in fats

(5) causes reproductive problems

(6) while DDT was banned in the US, in many countries it is still used.


E. Carbon Dioxide Emissions and the greenhouse effect

1) Carbon Dioxide emissions have caused the atmospheric CO2 concentrations to increase by 13% since 1958. Is due to combustion of fossil fuels and burning of weed removed by deforestation

1. some effects attributed to this raise in carbon dioxide are

a. we wee an increased productivity by vegetation

(1) C3 plants will start to take over C4 plant habitat

b) Temp increases will occur with increased carbon dioxide because they absorb infrared radiation and slows the escape of heat from the earth

(1) results in altered rain fall

(2) results in melting of ice caps possible flooding

c) Scientists are studying the records of pollen cores to determine how past temperature changes have affected vegetation.

F. Depletion of Atmospheric Ozone

1. atmospheric ozone is the protective layer in the stratosphere which absorbs ultraviolet radiation

a. release of chlorine gas reacts with ozone to break it down to regular oxygen

b. is a self renewed procedure so a little chlorine will affect a lot of molecules

c. ozone has decreased 2 to 10% in the past 20 years

2. Consequences of Ozone depletion

a. increase in skin cancer and cataracts

b. unpredictable effects on phytoplankton and other crops


8. Human activities that alter species distribution and reduce biodiversity

A. Introduction of Exotic Species

1. most transplanted species fail to survive, but many exceptions exist

a) starlings and English sparrows were introduced into the US in the 1800's, have displaced native birds in many areas

a. Fire ants

2. Release of genetically altered plants

a. may become pests in certain areas

b. may transfer some of the genetic characteristics to other plants

B. Habitat Destruction and the Biodiversity Crisis

1. Humans have destroyed much of the natural system

a. in US

(1) 15% of primary forest and 1% of tallgrass prairie remain

b. disruptive activities include: development, logging, war oil spills

2. Destruction of natural habitat will result in loss of biodiversity

a) even when we try and save endangered species, we do not know what we are doing? Therefore, we often make mistakes resulting in the loss of the organism

3) It is difficult do estimate the magnitude of the biodiversity crisis, because only a fraction of the earth's species have been identified, we do not know when something disappears when We do not even know it is present.

3. Estimates of how rapid extinction’s are occurring

a) populations of migratory songbirds in the Mid Atlantic US have been reduced by 50% in the last 40 years

a. 20% of all known species of freshwater fishes in the world are extinct

4. Current estimates

a. that rate of extinction is rapidly increasing

5. Why should we care about biodiversity

a) Biophilia, the human sense of connection to nature and other forms of life, is centered around aesthetics and ethics

b) Biodiveristy is a crucial natural resource and threatened species could provide crops, fibers, and medicines.

10. Sustainable Biosphere Initiative is reorienting ecological research

A. a way to acquire the basic ecological information needed for intelligent development, management, and conservation of the Earth's resources.

1. Global change including interactions between climate and ecological processes

2. Biological diversity and its role in maintaining ecological processes

3. How productivity from natural and artificial ecosystems can be sustained

B. The nature of ecological research will have to be reoriented but the importance can not be overstated due to the current state of the biosphere.




Ch 49 (1





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