The Biosphere AP Environmental Science

How does the Sun support life?

  • Lights and Warms the Planet
  • Powers the Cycling of Matter
  • Drives Climate and Weather-Causes the uneven heating of air and water that drives the distribution of those things around our Planet.
  • Enters the Living System through Producers and Photosynthesis


  • The energy from the sun is constantly moving through the Earth system, but it is not recycled.
  • First Law of Thermodynamics: Energy cannot be created or destroyed. So energy input is always equal to energy output.
  • Second Law of Thermodynamics: As the energy goes through a system the quality of that energy will decrease (entropy.) Most energy is converted to heat as it passes through the system.
  • The nutrients and the rest of the matter that are here on Earth is constantly being recycled and rarely ever leave the Earth system.

Gross vs Net Primary Productivity

Gross Primary Productivity is the total amount of energy (sugars) created by the producers through photosynthesis in a biome. Compare this to the paycheck you receive with all of the money you earned.

Net Primary Productivity is the amount of energy (sugars) left over for the rest of the biome to consume after the plants have respired and consumed some of what they created. Compare this to the money you have left after taxes have been taken out.

Left: Chart shows typical NPP for different biomes. Right: Energy pyramid that shows only 10% of energy is passed on to next trophic level. 90% is converted to lower quality heat.

The two charts above show the amount of energy available for each biome and at each trophic level in a food chain. Only 10% of the available energy is passed on to the next trophic level, while 90% is converted to lower quality heat energy. So the rainforest is one of the only biomes on the planet that can support 5 trophic levels for any period of time. See the Biomes Spark for more information.

Roles of Organisms

Generalists (r-selected species)

Cockroaches are perfect examples of generalists. These organisms can tolerate a wide range of conditions and consume a wide variety of resources. Other generalists:

Dandelions grow like weeds and scatter their seeds to the wind.
Raccoons can eat a variety of foods and adapt to a wide range of conditions.

Specialists (K-selected species)

Giant Pandas are specialists due to their ability to out-compete other organisms. They eat only bamboo, are very picky with choosing a mate, and live in very specific climatic conditions. Other specialists:

Saguaro Cacti live in very specific climatic conditions and are ideally suited to survive..
Killer Whales have specific migratory patterns, are very picky with choosing a mate, and nurture their young.

Indicator Species

The Northern Spotted Owl is a famous indicator species in the Pacific Northwest. These animals live in the old growth Giant Redwood trees. The owls are a threatened species, which indicates that the Redwoods are also being threatened. Other Indicator species include:

Trout and other fish are an indicator species, because if a bunch of fish kills occur, that indicates a larger water quality issue of some kind.
Amphibians are indicator species, because they are exposed to a variety of conditions in water and air throughout their life cycles. They have very absorbent skin and are sensitive to changes in an ecosystem.

Keystone Species

Sea Otters are a famous example of a keystone species. Oyster harvesters in the Pacific thought that the Otters were competing with them for the oysters, so they shot them whenever they saw them. The Harvesters did not realize that the Otters also kept the Kelp that grew on the ocean floor maintained where the oyster habitats were. When the Otters became ecologically extinct, the entire ecosystem collapsed. The otters have since started to recover. Keystone species in general have a substantial effect on the ecosystem through the services they provide and the interactions with other organisms.

This is what the food web looked like without the Sea Otters.

Other Keystone species include:

American alligators dig holes for aquatic ecosystems and clear mounds for migratory birds to rest on during their long flights north and south. These animals are endangered and could cause the collapse of the ecosystem with their absence.

Endangered, Threatened, Extinct

  • Threatened species are abundant in its natural range, but numbers are declining.
  • Endangered species have so few survivors it can experience ecological/biological extinction.
  • The United States Fish and Wildlife Service (USFWS) and the National Office for Atmospheric Administration (NOAA) are the two agencies responsible for identifying and regulating the Endangered Species Act.

There are four types of extinction:

  1. Ecological Extinction: There are not enough left to provide the ecological services they would normally add to an ecosystem.
  2. Commercial Extinction: There are not enough left to harvest for profit. (Fish usually)
  3. Local Extinction: No longer found in an area.
  4. Biological Extinction: No longer exists on this planet.
Clockwise from top left: The extinct Dodo bird and the extinct Passenger Pigeon, the endangered Mountain Gorilla, the endangered Rafflesia flower (rotting corpse flower), and the endangered Black Rhino.


Use this mnemonic device to determine if Human interaction is responsible for the endangerment of an organism.

  • Habitat Destruction and Fragmentation-MOST COMMON ANSWER
  • Invasive species
  • Population
  • Pollution
  • Climate Change
  • Overharvesting

For the rest of this unit, review the biology concepts from the Ecology Refresher reading guide.


Created with images by ddouk - "sunset sea sun" • Oldiefan - "flower tulips red"

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