Ecosystems and Productivity

Limiting Factors

• Light levels at ground level in a mature forest are a limiting factor, likely phosphorus toxicity.
• Certain soil nutrients (likely phosphorus) are another limiting factor in ecosystems.

Productivity

• Productivity is a measure of the output.
• Four factors support high productivity: light, water, nutrients (NPK), and temperature.
• Organisms that create food in an ecosystem are producers, also known as autotrophs.
• Autotrophs include plants, algae, and bacteria.

Measuring Productivity

• Productivity is measured as a rate, which is the amount per unit space and time.

Food Webs and Energy in Ecosystems

• Food webs allow examination of feeding relationships.
• Feeding roles:
  • Producers: make their own food.
  • Herbivores: eat vegetation.
  • Carnivores: eat other animals.
  • Detritivores: eat dead organic matter (invertebrates).
  • Decomposers (microbes): recycle nutrients in food.

Energy Flow and Food Webs

• Energy transformation is less than 100% efficient.
• The trophic pyramid (energy pyramid) shows how feeding levels transfer energy.
  • Producers occupy the base.
  • Primary consumers (herbivores) occupy the second tier.
  • Secondary consumers occupy the third tier.
  • Predators occupy the top tier.

Ecological Efficiency

• The trophic pyramid reveals ecological efficiency throughout several levels.
• Energy flows through an ecosystem.
• Only about 10% of energy is able to build at the next trophic level.

Energy Review

• Energy moves through an ecosystem as it flows.
• The source of energy for every ecosystem is the sun.
• The sun provides energy to producers who convert it to chemical energy.
• A trophic pyramid shows energy transfer at each level.
• Primary consumers occupy the second trophic level.
• When moving from one trophic level to another, the energy transfer is called ecological efficiency.
• 10% of energy is passed to the next level.

African Savanna Example

• Producer: trees (acacia, etc.)
• Herbivore: giraffe
• Carnivore: lion
• Omnivore: baboon
• Detritivore/Decomposers: bacteria, termites, fungi.