ECOLOGY: The Study of Ecosystems

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

The hierarchy. Define each of the following.

Ecology is a science, not a sociopolitical movement (e.g., environmentalism, conservation, etc.).

The Ecologist engages in the hypothetico-deductive method to pose questions and devise testable hypotheses about ecosystems. Often, this involves the generation of complex mathematical models to simulate ecosystems. These models represent idealized systems to which real systems can be compared for their predictive value. Sometimes, when a very large scale project is logistically impossible to perform, a computer model is used to predict expected results.

An ecosystem consists of

Evolution by natural selection is driven by ecological interactions.

Levels of Ecological Study

Because all organisms in ecosystems have evolved their place in the ecosystem over millennia, the link between evolution and ecology is vital to understand. That evolution is still happening around us, and we can be a major selective force. To avoid inadvertently creating disasters, we must understand that ecology and evolution are inextricably related.

One of the most important figures in the application of ecological principles to modern awareness of our role in the biosphere was Rachel Carson, author of Silent Spring (1962). In this work, in which she warned that the widespread, unregulated use of pesticides (e.g., DDT, now banned in the U.S., but not banned everywhere) would lead to environmental disaster.

Your assignment: Answer the questions in Concept Box 52.1 (page 1151) of your text.

Components of the Biosphere

The plant community of a particular region depends on the climate--the combination of temperature, water, light, and wind. And the flora directly affects the composition of the fauna.

Abiotic Components of Ecosystems

  • Temperature

  • Water

  • Sunlight

  • Wind

  • Rocks/Soil

  • Major Environmental Disturbances

    Global Patterns of 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.

    RECALL: Water has a very high specific heat (To raise 1g of water by 1oC requires 1.0 calorie, which is quite high, compared to other liquids).
    Thus, bodies of water are tremendous energy "sinks" that can absorb large amounts of solar energy with relatively little heating. (Solar radiation striking land causes far more heating than solar radiation striking land.)

  • Diurnally, land warms and air over it rises.
  • If there is a body of water nearby, cooler air from over the water is drawn over the land.
  • In the evening, the opposite occurs, warming the land with offshore, dry air.

    The North Side is where the moss grows...(unless you're in Australia)

  • In Northern Hemisphere, southern slopes receive high irradiance, and are warmer and drier.
    (The opposite is true in the Southern Hemisphere)
  • Lower irradiance northern slopes are cooler and wetter.
  • local flora usually reflects this difference in temperature and humidity:

    Mountains and Thermoclines

  • With every 1000m increase in elevation, average temperature decreases by about 6o C.
  • This means that mountain ecosystems at lower latitudes may have flora and fauna more similar to that of low elevation ecosystems at higher latitudes.
    (Examples...)

    Mountains and Rain Shadows

    When mountain ranges are close to large bodies of water, precipitation occurs on the windward side, leaving the leeward side relatively dry and with less vegetation. This is known as "rain shadow."

    Local Seasonality
  • wet and dry seasons in the tropics and to some extent, the subtropics (slight shift of wet/dry air seasonally is due to earth's 23/5o tilt)
  • upwelling (El Nino)

    Aquatic Seasonal Variations: Turnover

  • In winter, the coldest water (0oC) is just below the surface ice, and is progressively warmer at deeper levels (water is densest at 4oC, so guess what the temperature at the bottom of the lake is.) Water at the bottom is relatively oxygen poor.

  • In spring, as the ice melts with solar irradiation, surface water temperatures rise to 4oC, and sink. This eliminates the thermal layers, causing mixing of the temperature layers. Water is now more uniformly oxygenated

  • In summer, the densest water stays sunk at the bottom (4oC), and the sun continues to warm the water from the top, down. This results in a re-establishment of thermoclines with the warmest water at the top. Once again, water at the bottom is oxygen poor, water at the top is oxygen rich, limited by surface dissolution and minor mixing at the surface.

  • In autumn, colder temperatures cause surface water to cool rapidly. As it reaches 4oC, it sinks, disrupting the thermoclines and causing mixing. Water is once again more uniformly oxygenated. This continues until winter freeze, and the winter thermal profile is re-established.

    Aquatic and Terrestrial 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 - These 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...

    Stratification of Aquatic Biomes

    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.

    Zonation in Freshwater Biomes

    Classification of Freshwater Biomes by Productivity As you will learn later, productivity is a measure of how much biomass (dry organic matter) a particular ecosystem gains over a specified period of time. More on this later.

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

    Zonation in Marine Biomes

    Major Terrestrial Biomes