Click HERE for your print-friendly copy of the notes. Don't print the big font pages!

Ecology: The Study of Ecosystems

Ecology (from the Greek oikos meaning "house" or "dwelling", and logos meaning "discourse" or "study") - the study of interactions of organisms with each other and their environment.

Ecology is a natural science, not a sociopolitical discipline (such as environmentalism, conservation, etc.). Ecologists employ hypothetico-deductive methods to address ecological questions.

Ecology can be considered at many levels.

An ecosystem consists of

Evolution by natural selection is driven by ecological interactions.

Levels of Ecological Study

Ecology and evolution are inextricably related.

One of the first to apply ecological principles to modern awareness of our role in the biosphere was Rachel Carson, author of Silent Spring (1962).

Components of the Biosphere

Climate--the combination of temperature, water, light, and wind over time--of a region determines its flora. Climate and flora directly affect composition of the fauna.

Abiotic Components

  • Temperature

  • Water

    • contributes to soil erosion and creation
    • major component of organism habitats
    • Natural selection has been driven by
      • lack of water in terrestrial environments
      • lack of solutes in fresh water
    • animals that have secondarily returned to marine environments face different osmotic challenges: ocean is saltier than when their ancestors left it.
    • Green plants can be categorized on the basis of their adaptations for dealing with water availability in their habitat.
      • hydrophyte - adaptations for a very wet environment; for example:
        • thin cuticle
        • stomates on upper leaf surfaces, if leaves are floating
        • adaptations for obtaining nitrogen via the leaves instead of the soil (where acid conditons sequester nitrogen)
        • spongy, air-filled parenchyma to aid floating
        • may have specialized roots (pneumatophores) that protrude above water level to obtain oxygen

      • mesophyte - adaptations for a moderately wet environment

      • xerophyte - adaptations for a very dry environment; for example:
        • very thick cuticle
        • reduced leaves
        • stomates protected in grooves
        • pubescent (fuzzy) epidermis (protects against evaporation/desiccation)
        • water-filled tissues and/or organs

  • Sunlight

    • Life is strongly affected by sunlight
      • intensity
      • daily duration
      • angle of incidence of the sun (seasonal changes)
    • competition for light can be an important force driving natural selection
    • aquatic environment: community composition determined by depth, as photosynthetic pigments needed for deeper water are different from those on land and in shallow water.
    • photoperiodicity: The rhythm of certain biological phenomena (e.g., hibernation, reproductive cycles) are determined by the regularly recurring changes in light and dark caused by earth's rotation and its annual passage around the sun.

    • photoperiodicity can cycle
    • daily
    • monthly
    • annually
    ...depending on the biological activity.

  • Circadian rhythm: regular recurrence of a biological activity in cycles of approximately 24 hours.
    For example, sleep cycles occur at a regular intervals, regardless of constant darkness or other conditions of illumination.

  • Wind


  • Major Environmental Disturbances

    Review: Global Climate

    The ultimate source of climate is the sun, which provides not only the majority of energy on earth, but also creates climatic events when its randomizing energy interacts with the earth.

  • Less than half of the solar radiation striking the earth's atmosphere successfully penetrates the atmosphere to reach earth.

  • Terrestrial irradiance (i.e., solar radiation incident on the earth's surface) ranges from approximately 250nm (ultraviolet) to 1500nm (near infrared). Shorter and longer wavelengths are absorbed or reflected by atmospheric ozone, water vapor.

  • When the sun is directly overhead in a cloudless sky, solar irradiance (i.e., the sunlight that actually strikes the earth's surface) is most intense and peaks near 540nm ("green").

  • Environmental conditions and angle of incidence affect both intensity and spectral distribution of incident sunlight.

    Flora and fauna are profoundly affected by environmental and seasonal changes in solar intensity and spectral distribution. Note also that because the earth is tilted 23.5o on its axis (defining those tropical latitudes), there are seasonal changes in solar irradiation in both hemispheres:

    Solar warming of earth creates

  • global air and water vapor movement

    Climate can be affected locally by

  • proximity to ocean, lakes, rivers
  • topography

    This creates smaller, localized ecosystems within biomes.


    A biome is a major ecosystem spread over a wide geographic area, and characterized by certain types of flora and fauna.

    Major Aquatic Biomes

    Earth is sometimes called "the Water Planet." Aquatic biomes occupy most of the biosphere

    Life originated in the oceans, and stayed there for nearly 3 billion years. The oceans are the most influential of all terrestrial features affecting climate and biomes.

    Aquatic biomes may be

    The major types of aquatic biomes are...

    Aquatic Biome Strata

    Light is absorbed by water and by living aquatic organisms.

  • photic zone - light sufficient for photosynthesis
  • aphotic zone - light insufficient for photosynthesis

    Temperatures vary with depth, and aquatic habitats of any depth generally have a thermocline--a narrow band of water where temperature suddenly changes.

    Freshwater Biome Zones

    Marine Biome Zones

    Productivity in Freshwater Biomes
    Productivity is a measure of how much biomass (dry organic matter) a particular ecosystem gains over a specified period of time. Freshwater ecosystems/biomes can be characterized by their level of productivity.

  • oligotrophic - deep, nutrient poor, water very clear; LOW productivity
  • eutrophic - shallower, nutrient rich, murky with phytoplankton; HIGH productivity
    (note on cultural eutrophication)
  • mesotrophic - in between the above two classifications; MODERATE productivity

    Major Terrestrial Biomes

    Temperate Deciduous Forest




    Tropical Rainforest


    Note the link between soil nutrient content and precipitation. Consider...

  • Which of these biomes has the highest productivity?
  • Which has the lowest soil nutrient content?
  • Which has the highest soil nutrient content?
  • Which biomes are most most suitable for agriculture?
  • Which do you like the best? (That's the hardest question!)