• Biogeochemical cycles: describe flow of essential elements from the environment to living things and back to environment
    • Studies the rate of element movement between reservoirs & interaction of the current cycle with other cycles
  • FRQ: if question asks about flow of cycle, describe the input, use of element, and output
  • Decomposition on land slower in temperate bcuz less rain (so have more nutrients in soil)
    • Net primary production greatly exceeds the rate of decomposition in such ecosystems, causing them to store large amounts of organic matter.
  • Reservoirs: where elements/inorganic materials are stored
    • Ex: organisms, fossil fuels, water, soil, air, rocks (not directly available to organisms but slowly thru erosion)
    • Nutrients in organisms & detritus are available to other organism
  • Assimilation: elements incorporated into plants and animals
  • Release: processes which return elements to environment


Major Cycles

  1. Nitrogen cycle: nitrogen is required for the manufacture of all amino acids and nucleic acids
  • Reservoirs: atmosphere (N2); soil (ammonium [NH4] or ammonia [NH3], nitrite)
  • Assimilation: plants absorb nitrogen; animals obtain nitrogen by eating plants or other animals; stages in assimilation of nitrogen…
    • Nitrogen fixation: nitrogen-fixing bacteria transform atmospheric nitrogen to fixed nitrogen which is absorbed by plants
    • Nitrification: soil ammonia turned into nitrate for plants to absorb
  • Release: denitrification: NO3 back to N2; detritivorous bacteria convert organic
  1. Hydrologic cycle (water cycle)
  • Reservoirs: oceans, groundwater, glaciers (Evaporation, wind, and precipitation remove water from oceans to land)
  • Assimilation: plants absorb water from soil, animals drink water or eat other organisms
  • Release: plants transpire; animals and plants decompose
  1. Carbon cycle                                                                                               
  • Reservoirs: atmosphere, sediments, fossilized plant and animal remains (coal, oil, and natural gas), plant and animal biomass (as carbon) bodies of water, fossil fuels
  • Assimilation: plants use carbon in photosynthesis; animals consume plant or other animals
  • Release: plants and animals release carbon thru respiration and decomposition; carbon is released when organic material (ex: wood and fossil fuels) is burned
  • compounds back to NH4 (ammonification); animals excrete NH4
  1. Phosphorus cycle: phosphorus is required for ATP & nucleic acids; involves weathering of rocks
  • Reservoirs: ocean sediment, soil
  • Assimilation: plants absorb inorganic phosphate from soil; animals obtain organic
  • phosphorus when they eat plants or other animals
  • Release: plants and animals release phosphorus when they decompose; animals excrete in waste products


Extinction risks in small populations

  • Small populations particularly vulnerable threats to biodiversity such as overharvesting, habitat loss, inbreeding & genetic drift → smaller and smaller population → loss of genetic variation → extinction vortex towards smaller and smaller population
    • Inbreeding often reduces fitness because offspring are more likely to be homozygous for harmful recessive traits

Environmental Factors that Affect Biodiversity

Fragmentation and Edges

  • Edges: boundaries between ecosystems
    • Can provide both types of resources
  • Fragmentation: landscape divided into more isolated pieces
    • Can help some species and harm others: benefit disturbance-adapted and invasive species

Corridors That Connect Habitat Fragments

  • Movement corridor: a narrow strip of habitat connecting otherwise isolated patches
    • Important for conserving biodiversity in fragmented habitats; can be man-made
  • Movement corridors can also promote dispersal and reduce inbreeding in declining populations
    • Can be harmful by helping to spread disease

Human Population Growth

  • The following factors have increased the carrying capacity of the environment and made exponential growth possible
  1. Increases in food supply: domesticating animals and plants + increased food output bcuz of tech advances (ex: fertilizers and pesticides)
  2. Reduction in disease & human waste:
  3. Habitat expansion: immigrating to new areas

Human Impact on Ecosystems:

  • Human activity damages biosphere
    • Ex: exponential population growth, destruction of habitats for agriculture and mining, pollution from industry and transportation.

Consequences of Human Impact on Ecosystems

  1. Global climate change:
  • Some wavelengths of light reflected while rest absorbed by earth; earth re-emits some of radiation back to atomposhere → absorbed by CO2 and other greenhouse gasses
  • Population increase → so does human activity (burning of fossil fuels) → increase greenhouse gasses→ absorb more energy → temp of atmosphere & earth increases
    • Warming temp = rising sea levels, decade agricultural output (affect weather patterns), increase human disease (by broadening range of tropical disease vectors), and threaten extinction to species (disrupting environmental conditions to which species are adapted)
  1. Ozone depletion: ozone layer forms when as UV radiation reacts with oxygen to form ozone
  • Absorbs UV radiation and stops reaching surface of earth (would damage DNA of organisms)
  • Air pollutants break down layer → ozone holes → UV reaches surface
  1. Acid rain: burning of fossil fuels release into air pollutants with sulfur dioxide and nitrogen dioxide → react with water vapor → produce sulfuric acid and nitric acid → acids return to surface of the earth as rain → acidify soil and oceans
  2. Desertification: overgrazing of grasslands transform them into desserts → decrease agricultural output and habitats available
  3. Deforestation: cutting down forests causes increasing CO2 in atmosphere, loss of nutrients (since are stored in trees roots), habitat (& species) loss, and erosion
  4. Pollution: contaminate materials essential to life
  • Pollutants remain for long time; toxins concentrate in plants and animals
  • Biological magnification: one organism eats another and further concentrates toxin
  • Algal blooms: massive growths of algae and other phytoplankton when lake polluted with runoff fertilizer or sewage → add nutrients
  • Eutrophication: process of nutrient enrichment in lakes and increase in biomass
    • Results in oxygen depletion, fishes dying, and growth of anaerobic bacteria that produce foul-smelling gasses
  1. Reduction in species diversity: human impacts are causing plant and animals to become extinct at a faster rate 

                    Reduction in plants that could become useful to humans as medicines or food