Ecosystems

• An ecosystem has a biotic unit and an abiotic unit; living vs. non-living
  • Biotic: organisms, community, prey/food
  • Abiotic: oxygen, nutrients, water (and the availability of all of these units)
• Limiting factors: the combination of biotic and abiotic factors which can check the size of a population
• An ecosystem is divided into:
  • Producers/Autotrophs: Plants and cyanobacteria
  • Consumers: Animals
  • Decomposers: Bacteria, fungi, microorganisms
• Ecosystems contain complexity through species stability and carrying capacity
  • Carrying Capacity: the maximum population that an ecosystem can support in the long term
    • Carrying capacity is never in stasis, but fluctuates around a given average depending on environmental factors
  • Stability prevents extinction and population die-offs; instability is induced by reducing attachments to a greater food web

Producers

• Autotrophic processes: Photosynthesis and Chemosynthesis
  • Photosynthesis converts sunlight energy into chemical energy; carbon dioxide → oxygen, and light energy → sugars (glucose); plants and cyanobacteria
  • Chemosynthesis converts chemicals (sulfur) into carbon compounds; bacteria
• Producers undergo cellular respiration, but use less glucose and oxygen than they photo/chemosynthesize
• Gross Primary Productivity (GPP): the total amount of energy converted from an inorganic form to an organic form
  • Net Primary Productivity (NPP): the amount of organic energy remaining after part of the gross primary productivity is consumed by producers to survive
    • Net productivity is determined via biomass and cells (in units of g/m^2 per year)
    • Tropical rainforests, marshland/estuaries, & coral reefs have the highest productivity at 2,500 g/m^2
    • Temperate evergreens follow at 1,300 g/m^2
    • Woodlands at 700 g/m^2
    • Cultivated land is around 650, but can value much higher
    • Deserts lowest at 90 g/m^2

Consumers and Decomposers

• Both are heterotrophs
  • Consumers, Detritivores, and Decomposers
• Sole heterotrophic process: cellular respiration
• Food web; primary, secondary, tertiary consumers, etc.

Energy Transfer Efficiency

• Only 10% of the total energy is net transferred across each trophic level; all of the energy is consumed, but the 90% excluded is burned in order to consume prey and maintain processes to stay alive
• This net transfer/loss includes energy obtained by decomposers

O=C=O.O>>O=C(O)C(O)C(O)C(O)C(O)C.O=O
O=C(O)C(O)C(O)C(O)C(O)C.O=O>>O=C=O.O

Ecosystem Cycles

• various methods of nutrient cycling

Carbon Cycle

• primarily in the form of a gas, CO2

1. CO2 is used in photosynthesis by producers and converted
2. Heterotrophs consume organic forms of energy which were made from CO2
3. Heterotrophs perform cellular respiration, releasing CO2

Nitrogen Cycle

• Nitrogen is the basis of proteins and DNA (nucleic acid)
• 78% of the atmosphere is stable nitrogen gas; difficult to break apart
• Nitrogen-fixing bacteria converts nitrogen into ammonia
  • Prominently performed by cyanobacteria
  • Nitrifying bacteria in soil
• Algae blooms in excess nitrogen

1. Nitrogen gas is converted by bacteria to solid ammonia
2. Ammonia is biologically assimilated into bacteria
3. Bacteria undergoes decomposition

• Two outcomes:
  1. Decomposed ammonia is taken in by plants/cycled
  2. Or ammonia is denitrified; converts back into nitrogen gas
     • Denitrifying bacteria

Phosphate/Phosphorus cycle

• Phosphorus: nutrient in the soil, uptake by plants, use in animal skeletons, genetic material, ATP

1. Phosphorus is used in photosynthesis by producers and converted into glucose
2. Heterotrophs consume glucose
3. Heterotrophs release phosphorus via cell respiration and decomposition

Water/Hydrologic Cycle

• Not a nutrient, but a major component (photosynthesis)
• Complex; ground, surface, plant components involved
• A system of flows and stores

1. Evaporation off of a body of water/source; sunlight/heat energy converts into vapor
   • Evapotranspiration in plants → evaporation
2. Vapor rises through altitude levels and cools; water molecules are dense; condensate, bind, and attract via polarity; reduces surface space
3. Cloud mass forms and cools; water droplets are pulled by gravity → precipitation as rain, hail, sleet, snow

• Multiple outcomes:
  • Plant uptake; water loss becomes transpiration
  • Surface runoff on hardscape or oversaturated surfaces
  • Infiltration into ground → groundwater