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Bottom-up control: Resource supply determines trophic structure. Bottom-up control is the influence of producers on the sizes of the trophic levels above them in a food web.

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Bottom-up Control

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  • Bottom-up control: Resource supply determines trophic structure. Bottom-up control is the influence of producers on the sizes of the trophic levels above them in a food web.

  • Top-down control: Predation and grazing by higher trophic levels on lower trophic levels ultimately controls ecosystem function.

  • Biomagnification: Increase in concentration of the contaminant from one link in a food chain to another

  • Question of the Day: What happens to energy as it is passed from producers to consumers?


Bottom-up Control


Top-down Control


Biomagnification


Biomagnification

  • Populations of many predatory and fish-eating birds in the United States declined in the 1950s and 60s

  • The causes of these population declines were traced to pollution of aquatic habitats by residues of DDT

  • DDT is a pesticide that was used to control crop pests after World War II


Biomagnification

  • The pesticide’s residues resisted degradation and entered aquatic food chains

  • DDT residues accumulated in the fatty tissues of animals and were concentrated with each step in the food chain

  • The high doses consumed by predatory birds interfered with their physiology and reproduction, making their eggshells excessively thin and causing the deaths of embryos

  • Breeding success declined, and populations followed


Biomagnification

  • DDT affected wildlife and non-target species

  • The peregrine falcon was a sensitive indicator of the health of the environment


Nitrogen and Carbon Cycles


How do chemicals cycle through an ecosystem?

  • Carbon dioxide in the atmosphere

  • Carbon dioxide in decaying matter

  • Carbon dioxide in fossil fuels underground

  • Plants use of carbon during photosynthesis

  • Animals obtaining carbon from plants

  • Animal respiration and plant respiration


The carbon cycle is closely tied to the flow of energy through the biosphere

  • Classes of processes cause carbon to cycle through ecosystems

    • Photosynthesis and respiration

    • Ocean-atmosphere exchange

    • Deposition and burial, Volcanic release


Global Carbon Cycle


Photosynthesis and Respiration

  • Photosynthesis and respiration are the main energy transforming reactions of life

  • Photosynthesis is the conversion of light energy to chemical energy that is stored in glucose or other organic compounds

  • Respiration is the use of oxygen to metabolize organic compounds and release chemical energy


Photosynthesis and Respiration

  • During photosynthesis, carbon gains electrons and is reduced, this is accompanied by a gain in chemical energy

  • An equivalent amount of energy is released by respiration, which results in a loss of electrons and a loss of chemical energy


Photosynthesis and Respiration

  • About 85 billion metric tons (1 billion metric tons is a gigaton) of carbon will enter into these reactions each year

  • There is something like 2,650 gigatons of total carbon in organic matter


How is carbon extracted from the atmosphere?

  • Carbon is extracted from the atmosphere through plants in a process called photosynthesis.

  • What are ways in which carbon is released into the atmosphere?

  • Carbon can be released into the atmosphere by animal respiration (when animals breathe out), by plant respiration,


Ocean-atmosphere exchange

  • Physical exchanges of carbon dioxide between the atmosphere and oceans, lakes, and streams

  • Carbon dioxide dissolves readily in water

  • The oceans contain about 50 times more carbon dioxide as the atmosphere does

  • Carbon dioxide is continuously being exchanged across the boundary between the oceans and the atmosphere


Ocean-atmosphere exchange

  • Exchange across the air-water boundary links the carbon cycles of terrestrial and aquatic ecosystems

  • The ocean is an important sink for the carbon dioxide produced by the burning of fossil fuels


Deposition and burial

  • In the atmosphere, atmospheric carbon dioxide reacts with water to form carbonic acid 

  • Carbonic acid will fall to the earth as rain and reacts with minerals at the earth’s surface

  • Through the process of chemical weathering, carbonic acid will slowly dissolve these minerals into their component ions 

  • These component ions are carried in surface waters like streams and rivers eventually to the ocean

  • Component ions precipitate out as minerals like calcite and through continued deposition and burial, this calcite sediment forms limestone


Deposition and burial

  • This cycle continues as subduction occurs

  • As seafloor carbon is pushed deeper into the earth by tectonic forces, it heats up, this causes it to melt

  • It then can rise back up to the surface, where it is released as CO2 and returned to the atmosphere.

  • This return to the atmosphere can occur through volcanic eruptions


Human Driven Carbon Flow

  • Release of carbon from fossil fuels and land use change

  • The rise in atmospheric CO2 leads to increase in global temperature

  • Fossil Fuels were formed millions of years ago from plant or animal remains that were buried, compressed, and transformed into oil, coal, or natural gas

  • The carbon is said to be "fixed" in place and is essentially locked out of the natural carbon cycle


Human Driven Carbon Flow

  • Humans intervene by burning the fossil fuels

  • During combustion of fossil fuels, carbon dioxide and water molecules are released into the atmosphere


What happens to the carbon in plants and animals when they die?

  • They decay, and the carbon is released back into the ground. Some of the carbon gets buried far underground and will become fossil fuels after many millions of years.

  • What is one way in which carbon is released into the atmosphere?

  • Carbon can be released into the atmosphere when humans burn fossil fuels.


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