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ECOSYSTEM ECOLOGY: The Big Picture

You've probably seen pictures of Food Webs. The "levels" of the web--which organisms eat which one's "lower" on the chain"--are called TROPHIC (from the Greek troph, meaning "food" or "nourishment") LEVELS.

The Food Web reflects the flow of ENERGY and NUTRIENTS through ecosystems via the trophic levels.

  • Autotrophs: Organisms that can feed themselves by harnessing light energy (or in some cases, chemical energy, as in deep sea trenches) to make organic molecules such as carbohydrates, proteins, lipids, and nucleic acids out of inorganic raw materials (such as carbon dioxide, water, nitrogen compounds, etc.)

  • Heterotrophs: Organisms that feed on other organisms to obtain energy.

    Autotrophs are also called PRIMARY PRODUCERS, because they are the first link in the food web/chain. Without their ability to capture light and "harness" it as solid, organic matter, life as we know it would not exist.

  • Primary Producers are eaten by PRIMARY (1o) CONSUMERS.

  • Primary Consumers are eaten by SECONDARY (2o) CONSUMERS.
  • Secondary Consumers are eaten by TERTIARY (3o) CONSUMERS.
  • Tertiary Consumers are eaten by QUATERNARY (4o) CONSUMERS
    ...and so on, throughout the web.

    Herbivore: Animal that eats plant matter. Herbivores may also be

  • frugivores
  • seed eaters

    Carnivore: Animal that eats meat. Insectivore: Animal that eats insects. Omnivore: Animal that eats a variety of different foods, both plant and animal.

    You can make up a "vore" term for anything. (What would you call a Koala, who eats only the leaves of Eucalyptus trees?)

    The result of all this feeding, though, is a cycling of both ENERGY, and various chemical elements and compounds (carbon, nitrogen, phosphorus, water...almost anything that temporarily inhabits a living thing) through the biosphere.

    Note that ENERGY FLOW is one-way trip. All energy flowing through an ecosystem dissipates, and is not recycled through the system. Recall the Laws of Thermodynamics:

    This means that although nutrients can cycle and recycle through the system via the action of primary producers and decomposers, energy must constantly be replenished via photosynthesis: the capture of randomizing energy from the sun.

    Energy flow is never 100% efficient, and this results in the classic Pyramid of Productivity.

    (The efficiency with which trophic levels convert energy from the previous trophic levels varies greatly with ecosystem, but usually ranges between 5% - 20%.)

    Many toxic substances produced by human activity, such as petroleum-based pesticides, and other toxins, are fat-soluble. When a consumer eats them, they remain sequestered in the fatty tissue, and are not excreted. When such a "contaminated" animal is eaten, in turn, by predators at higher trophic levels, the toxins increase in concentration, depositing in the fatty tissues.

    The higher the trophic level, the greater the risk of fat-soluble toxin acquisition and concentration in the tissues. This is known as BIOLOGICAL MAGNIFICATION.

    Ecosystem Ecologists are concerned with the study of these energy and nutrient pathways, which are called BIOGEOCHEMICAL CYCLES. A generalized cycle...

    ...can be superimposed on Biogeochemical Cycles for many different nutrients

    Your activities any day have profound effects on these cycles, and on energy cycling in the biosphere. To test how much impact you have on our biosphere, take the following test of your Ecological Footprint.

    Take a moment to read this article, "Imagine Earth without People".

  • Ecological niche - The sum total of a species' use of the biotic and abiotic resources in its environment. Defined by the species, the ecological niche is everything that an organism eats, where it nests, sleeps, forages, etc. In short, everything that defines its natural history, including all its symbiotic relationships with other species.

    Two species can never occupy exactly the same ecological niche, or one will eventually out-compete the other, and the loser will become extinct. However, the niches of different species may overlap to some degree. When this happens, interspecific (i.e., between species) competition occurs.

  • Keystone species - species on which many other populations ultimately depend for survival.

    EXAMPLES:

     

  • Indicator species - a species whose population density allows humans to gauge the health of an entire ecosystem

    EXAMPLES:

     

  • Native species - a species found in the place where it naturally evolved. Native populations often have complex and delicately-balanced interactions with one another that can be disrupted by the introduction of exotic species.

    EXAMPLES:

     

  • Exotic species - a species living in a place where it did not originally evolved. These are often introduced by humans into ecosystems where they do not naturally belong. Some exotic species introduced into new environments are much better able than native species to compete for resources, and they can sometimes displace native species. This can have very profound effects on the other native species which used to rely on a native species driven extinct (or to great scarcity) by an invasive exotic.

    EXAMPLES:

     

    The Trouble with Exotic Species

    Florida examples:

  • Cajeput (Paperbark) tree (Melaleuca quinquenervia)
  • Australian pine (Casuarina equisetifolia)
  • Brazilian pepper(Schinus terebinthifolius)
    --all very invasive, pernicious "weed" species that out-compete native species and can eventually lead to native species extinction.

    They are also ALLELOPATHIC--producing toxic compounds that are meant to deter growth of other competing plants nearby.
    (As we already know, this can be valuable to humans seeking bioactive compounds--but don't assume that a product labeled "natural" is safe. Those plants mean business.)

    For more information on Exotic Invasive Plant Species in southern Florida, visit:

  • U.F. Hendry County Cooperative Extension Office
  • University of Florida Center for Aquatic and Invasive Plants