The Lessons on the Lake Logo Chapter 7: Ecosystems in Delicate Balance
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Lessons on the Lake -> Chapter 7 -> Ecosystems


An ecosystem can be thought of as a natural unit (e.g., wetlands, pine forests, or the entire Lake Pontchartrain Basin) consisting of living and non-living parts which interact to form a stable system. Examples of living and non-living parts include plants, animals, soil chemistry, temperature, nutrient supply, etc. Ecosystems in their natural state are finely-tuned and well-balanced. Ecosystems support and depend upon a tremendous diversity of plants and animals. Large numbers of animals and plants in the ecosystem indicate higher levels of biodiversity and greater complexity.

  • The Sun provides energy to Producers (green plants and algae, etc.).

  • Producers provide energy to Primary Consumers (herbivores or organisms that eat only plants).

  • Primary Consumers provide energy to Secondary Consumers (carnivores are animals that eat herbivores and omnivores are animals that eat both plants and animals).

  • Secondary Consumers provide energy to Tertiary Consumers (carnivores and scavengers who occupy the tops of their respective food chains, like eagles or humans).

  • Decomposers are microorganisms like bacteria and fungi which cause a breakdown of dead organic tissues (plants and animals), releasing their stored nutrients for re-use.

  • Nutrients released by decomposers are re-used by producers, starting the cycle over.

  • A certain amount of energy is lost in each stage of the food chain. This effectively limits the overall length of any given food chain. In other words, at some point, the energy spent getting food is greater than the energy gained from the food source, so an animal becomes weaker and weaker as time goes on until death finally occurs.

Increased biodiversity provides a more stable ecosystem because responsibility for various “jobs” are shared.

  • When humans interfere with delicate ecosystems, the most common result is severe disruption of natural balances which, in turn, results in greatly reduced ecosystem function.

  • When agricultural runoff and sewer discharges (unnaturally high levels of fertilizer)
    are emptied into Lake Pontchartrain, a dramatic increase in algal growth can be the result. This results in turbid or cloudy water. Aquatic plants die because they can’t get the same levels of sunlight, and algae blooms deplete aquatic systems of necessary oxygen.

  • As aquatic plants die, small fish which depend upon these plants also begin to die. In turn, larger fish which depend upon the smaller fish also die or leave. This represents the beginning of ecosystem collapse.

All is not lost, however!

Much of the damage we inflict upon the world around us can be
lessened or even reversed if we pay attention to the little changes in our
ecosystems. Each of us can contribute by reducing the amount of runoff
which enters the Lake Pontchartrain Basin and educating
others about the importance of maintaining balanced ecosystems.

"Think Globally, Act Locally"

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Unable to turn their heads sideways, a manatee must move its entire body to look in different directions.
  1. Ch. 7 Intro
  2. Essential Questions
  3. Ecosystems
  4. Energy Flow Through an Ecosystem
  5. Healthy vs. Unhealthy Ecosystems
  6. Biodiversity
  7. Threatened and Endangered Species in the Basin
  8. Decision Making and Issue Analysis
  9. Ecosystem Tumble
  10. Activity: I'm a Survivor