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

BiomagnificationPopulations of many predatory and fish-eating birds in the

United States declined in the 1950s and 60sThe causes of these population declines were traced to

pollution of aquatic habitats by residues of DDTDDT is a pesticide that was used to control crop pests after

World War II

BiomagnificationThe pesticide’s residues resisted degradation

and entered aquatic food chainsDDT 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

BiomagnificationDDT affected wildlife and non-target speciesThe 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 atmosphereCarbon dioxide in decaying matterCarbon dioxide in fossil fuels undergroundPlants use of carbon during photosynthesisAnimals obtaining carbon from plantsAnimal respiration and plant respiration

The carbon cycle is closely tied to the flow of energy through the biosphereClasses of processes cause carbon to cycle

through ecosystems Photosynthesis and respiration Ocean-atmosphere exchange Deposition and burial, Volcanic release

Global Carbon Cycle

Photosynthesis and RespirationPhotosynthesis and respiration are the main

energy transforming reactions of lifePhotosynthesis 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 RespirationDuring 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 RespirationAbout 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 exchangePhysical exchanges of carbon dioxide

between the atmosphere and oceans, lakes, and streams

Carbon dioxide dissolves readily in waterThe oceans contain about 50 times more

carbon dioxide as the atmosphere doesCarbon dioxide is continuously being

exchanged across the boundary between the oceans and the atmosphere

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

Ocean-atmosphere exchange

Deposition and burialIn 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 surfaceThrough 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 burialThis cycle continues as subduction occursAs 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 FlowRelease of carbon from fossil fuels and land

use changeThe rise in atmospheric CO2 leads to increase

in global temperatureFossil 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 FlowHumans intervene by burning the fossil fuels During combustion of fossil fuels, carbon

dioxide and water molecules are released into the atmosphere

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

What is one way in which carbon is released into the atmosphere?Carbon can be released into the atmosphere when humans burn fossil fuels.