BIOLOGY 281 Unit 4

• Energy transformers: Light energy + CO2 + H2O

  • (through photosynthesis) > chemical energy 
  • (though respiration) > work and heat
• Pools: the amount of material this is present in a given compartment
• Fluxes: the amount of material that is moving among the compartments during a given period of time
• Turnover rate: the proportion of a given pool which leaves during a given time

  • output / exiting pool = percentage per year
• Residence time: average length of time that a given element/matter will remain in a pool

  • pool / output = time
• The most dominant primary producers are photoautotrophs.
• Gross primary production: amount of C fixed within an ecosystem over some time period
• Net primary production: GPP minus the amount of C used by autotrophs for metabolism
• Secondary production: amount of C passed on to heterotrophs within the ecosystem
• NPP can be estimated using satellite-measured chloroplast reflectance, since the organelle is indicative of primary producers.
• NPP is constrained by physical and abiotic environmental factors like precipitation, temperature, and nutrients.
• Limiting factors of NPP: production was estimated from aboveground biomass in Hawaii, and shows that NPP decreases with increasing mean annual precipitation (less sunlight for photosynthesis)
• Plants allocate the most growth to capture limiting nutrients, which can depend on the environment

  • ex: in nutrient-poor biomes like tundras and grasslands, over 50% of NPP is allocated to growth of roots
  • ex: if competition for light is more important, less NPP is dedicated to roots
• Linear food chain: energy flows from 1st to 4th trophic level

  • Producers: 1st trophic level
  • Primary consumer: 2nd trophic level
  • Secondary consumer: 3rd trophic level
  • Tertiary consumer: 4th trophic level
• • Trophic efficiency: (PN/PN-1) * 100
  • PN = production of one trophic level
  • PN-1: production of trophic level below it
  • Consumption efficiency: % of available energy that is ingested by primary consumers
  • (IN/PN-1) x 100
  • Assimilation efficiency: % of energy in ingested material that is assimilated for metabolism by the primary consumers
  • (AN/IN)
  • Production efficiency: % of assimilated energy that is allocated to growth or production of offspring of the primary consumers
  • (PN/AN)
• Biomagnification: toxins like DDT (pesticide) and mercury (heavy metal) do not break down easily and accumulate at higher trophic levels, usually in predator species
• Where do nutrients come from?

  • Biological fixation
  • Weathering of rock
  • Fertilization
  • Plants and animals
  • Atmospheric deposition (dust and rain)
• The triple bond in gaseous nitrogen (N2) makes it extremely stable and thus chemically inert without massive inputs of energy.
• Inorganic N: not derived from organisms

  • ex: ammonia (NH3), ammonium (NH4+), nitrate (NO3-)
• Organic N: derived from organisms

  • ex: amino acids, proteins, etc.
• Microbial sources of N fixation and thus reactive N include:

  • Anaerobic bacteria
  • Aerobic bacteria
  • Photosynthetic bacteria
  • Cyanobacteria
• N fixation requires energy, which primarily comes from carbon fixation. The process also requires nitrogenase enzyme and low O2
• Nitrogen cycle:

  • Fixation: crucial because plants can’t take up N2 gas, but can take up ammonia in soil solution (N2 > NH3)
  • Nitrification: microbes convert ammonia into nitrate NO3- (NH3- > NO2- > NO3-)
  • plants can also up nitrate more easily than ammonia
  • Denitrification: microbes convert nitrate back into N2 gas (NO3- > NO > N2O > N2)
• Immobilization: conversion from inorganic to organic forms of N

  • ex: ammonia (NH3) or nitrate (NO3-) entering plant and animal food webs
• Ammonification (mineralization): organic forms of N are converted to NH4+ (e.g. in urine)

  • NH4+ is toxic in high concentrations and so must be excreted
• Major pools of N include the atmosphere, deep ocean, soil organic matter, and terrestrial biomass.
• Note that the largest fluxes in global N cycle are internal recycling in marine and terrestrial environments.

  • This describes the rapid movement of N back and forth between the biotic and abiotic pools (= immobilization and ammonification) without return to the atmosphere
• N fixation in terrestrial ecosystems is increased due to…

  1. widespread planting of N-fixing plants in agriculture
  2. N fixation from industrial sources
• Nitrous oxide (N2O) is a greenhouse gas released during nitrification and denitrification and during the burning of fossil fuels

  Per molecule, it has around 300 times the warming power of CO2.
• P does not exist in a gaseous phase, so does not cycle through atmosphere. Most of it is stored in rocks and marine sediment.
• Fungi can take up P more easily than plants; this is the basic for many mutualisms.
• Disturbance: a relatively discrete event that disrupts the structure of an ecosystem, community, or population by changing the physical environment or the resources it contains
• Climax: a stable biotic community that represents the last stage of succession
• Early succession species tend to have r-selected traits because these populations tend to grow rapidly, while late succession species tend to have K-selected traits.
• Chronosequence: similar habitats differing only in the time of post-disturbance succession

  • Cooper proposed 3 succession stages in Glacial Bay
  • Fausti proposed differences between old and young sites
• The Mount St. Helens eruption in 1980 showed that disturbance intensities play a large role in succession, as areas farther away from the site had residuals (remnant organisms) allowing for quicker recovery.
• Model of succession: in facilitation, pioneer species are first to arrive and favorably modify the environment for later successional species.
• Model of succession: in inhibition, both early and late succession species colonize a disturbed habitat and have equal opportunity to secure a space.

  Because late-succession species live longer, they become dominant over pioneer species.
• Model of succession: in tolerance, both early and late succession species colonize a disturbed habitat.

  Because late-succession species can tolerate conditions of limiting resources, they become dominant over pioneer species.
• Properties of wildfire include fire intensity and fire frequency.