BISC 130 - Chapter 46: Ecosystems

Ecosystems

• All of the living things in a particular area (community) together with the abiotic (nonliving) parts of that environment.

• Terrestrial: on land

• Aquatic: in the water

  • Freshwater

  • Marine (salt water)

• Terrestrial ecosystems are further divided into biomes, based on temperature and precipitation.

• Members of an ecosystem can be organized into a:

Food Chain

• Positions in the chain are called Trophic Levels.

Primary Producers

• Usually photosynthetic

• Autotrophs - an organism that gets carbon from inorganic sources

  • Eaten by:

• Primary consumers aka. Herbivores

  • These are Heterotrophs

• Primary consum. are eaten by secondary consumers

  • They are thus Heterotrophs.

• Secondary consumers, Heterotorophs, are eaten by:

• Tertiary consumers - Heterotrophs, etc. until, top/apex consumer.

• Dead organisms (of all levels) and their wastes are consumed by decomposers

  • These decomposers are Heterotrophs

• These relationships can also be diagrammed as a holistic, nonlinear "food web"

  • Species can occupy multiple levels

• Energy enters most ecosystems from the sun

  • It is harnessed by photosynthesis

    • Energy is transferred within food chains/webs

      • Some energy is lost to heat with each transfer.

• At higher levels;

  • There is less energy

  • Fewer individuals

  • Less biomass

• Matter cannot be created or destroyed

  • Certain compounds and elements are reused in:

Biogeochemical Cycles:

Carbon Cycle

• Organic compounds are based on carbon

• CO2 in air, bicarbonate in water

  • Fixed into organic compounds (ex: glucose) by photosynthesis

  • Cellular Respiration releases carbon back to CO2/bicarbonate

Water Cycle

• Living things need water

  • Solvent for living things

• Water evaporates from lakes, oceans, brooks

  • Energy for this by heat from the sun

• Water vapor (in air) condenses to precipitation

Nitrogen Cycle

• Nitrogen is needed for proteins and nucleotides

  • Vital element

• Nitrogen in the air (N2) is fixed into usable form (NH3) by special bacteria

  • N2 is abundant in the air

  • NH3 is often limited in the soil

• Decomposing bacteria convert fixed nitrogen back to N2 (gaseous nitrogen)

Phosphorus Cycle

• Phosphorus needed for nucleotides, lipids

  • Vital element

• Phosphorus can be aerosolized, but there is no common gas form

  • Therefore no fixation needed

• Used by organisms, and broken down to soluble phosphates in water and soil.

Sulfur Cycle

• Sulfur is needed for certain amino acids

  • Vital element

• Sulfur in air precipitates - no fixation needed

• Used by organisms, decomposition releases it back to the air.

• Limits on the growth of life in an ecosystem are defined by the compound or element that is most limited

------------------------------------------END OF LECTURE 5-2-----------------------------------------------