Energy in Ecosystems and Food Chains

Energy in Ecosystems

• Life in an ecosystem requires a source of energy.

Primary Energy Sources

• The primary source of energy on Earth is the sun.
• Producers provide energy for other organisms.
  • Obtain energy from non-living resources.
  • Also referred to as autotrophs because they make their own food.
  • Examples include plants, cyanobacteria, and some archaea.

Energy Acquisition Methods

• Almost all producers utilize sunlight as an energy source through photosynthesis.
  • Photosynthesis Process:
  • ( ext{Carbon dioxide} + ext{water})
    ightarrow ext{sugar} + ext{oxygen}
• Some prokaryote producers, like archaea, utilize chemosynthesis.
  • Chemosynthesis Process:
  • ( ext{Carbon dioxide} + ext{water} + ext{hydrogen sulfide} + ext{oxygen})
    ightarrow ext{sugar} + ext{sulfuric acid}

Consumers

• Consumers must consume other organisms to obtain energy.
  • They are called heterotrophs since they feed off various living or once-living resources.
  • All organisms need materials to synthesize nucleic acids, proteins, lipids, and carbohydrates for growth and repair.

Types of Consumers

• Consumers can be categorized as follows:
  • Herbivores: Only eat plants.
  • Carnivores: Only eat animals.
  • Omnivores: Eat both plants and animals.
  • Decomposers/Detritivores: Break down organic matter into simpler compounds.

Food Chains and Food Webs

• Food chains and food webs model the flow of energy in an ecosystem.
• Law of Conservation of Energy: Energy and matter are neither created nor destroyed; they merely change form.
  • Energy flows from the sun to producers, then to consumers and decomposers.
  • Some energy is lost as heat during transformations.

Food Chains

• A food chain shows a linear sequence of feeding relationships, linking species by their feeding interactions.
• Example: GRAASS → DESERT COTTONTAIL → HARRIS’S HAWK.

Food Webs

• A food web illustrates a complex network of feeding relationships, emphasizing the multiple feeding interactions within an ecosystem.

Trophic Levels

• Trophic levels denote nourishment levels in a food chain:
  • Primary consumers: Herbivores that eat producers.
  • Secondary consumers: Carnivores that eat herbivores.
  • Tertiary consumers: Carnivores that eat secondary consumers.
  • Omnivores: Can occupy multiple trophic levels depending on their diet.

Pyramid Models

• Pyramids are used to model the distribution of energy and matter within an ecosystem.
• An energy pyramid shows energy distribution among trophic levels.
  • Producers hold the most energy; top consumers hold the least.
  • Up to 90% of energy is lost between levels as heat (known as the 10% Rule).

10% Rule

• The 10% Rule explains diminishing population sizes through trophic levels:
  • When organisms consume one another, the majority of energy is lost as waste or heat rather than being converted to biomass.
  • More biomass is needed at lower trophic levels to sustain fewer organisms at higher trophic levels.

Biomass Measurements

• Biomass measures total dry mass required to support organisms across trophic levels.
• Example values for biomass:
  • Producers: 2000 ext{ g/m}^2
  • Primary consumers: 675 ext{ g/m}^2
  • Secondary consumers: 150 ext{ g/m}^2
  • Tertiary consumers: 75 ext{ g/m}^2

Pyramid of Numbers

• A pyramid of numbers illustrates the number of individuals required at each trophic level to support the next.
• Example values:
  • Producers: 5,000,000
  • Primary consumers: 500,000
  • Secondary consumers: 50,000
  • Tertiary consumers: 5
• Indicates a vast number of producers is necessary to support few top-level consumers, emphasizing the 10% Rule.