Food Chains, Webs, and Trophic Levels

• All organisms require energy to survive.
• Plants use light energy to produce food, animals consume plants or other animals.

Food Chains

• A food chain is a linear sequence showing how organisms feed on each other in an ecosystem.
• Food chains illustrate how nutrients and energy are transferred between organisms.

Food Webs

• A food web consists of interconnected food chains.

Trophic Levels

• Trophic levels define an organism's position in a food chain or web.
• Organisms can occupy multiple trophic levels based on their diet.
• Level 1: Primary producers create their own food.
• Level 2: Primary consumers eat primary producers.
• Level 3: Secondary consumers eat primary consumers.
• Level 4: Tertiary consumers eat secondary consumers.
• Level 5: Quaternary consumers eat tertiary consumers.

Autotrophs vs. Heterotrophs

• Producers are autotrophs, using photosynthesis to convert light energy into chemical energy.
• Consumers are heterotrophs, gaining energy from consuming plants or animals.
• Herbivores consume plants.
• Carnivores consume animals.
• Omnivores consume both plants and animals.

Energy Flow

• Producers convert light energy to chemical energy, which then flows to consumers.
• Energy transfer between trophic levels is inefficient; much energy is lost.
• Energy is lost because only part of the organism is eaten.
• Energy is lost because not all parts are digested
• Energy is used for life processes like growth, movement and reproduction.
• Energy loss occurs through respiration as heat.
• Energy is lost when organisms die.
• Approximately 10% of energy transfers to the next trophic level.
• Food chains typically have no more than 5 organisms due to energy loss at each level.
• Energy flows in one direction from producers to consumers to decomposers and is not recycled.

Decomposers and Detritivores

• Both are crucial for recycling chemical elements in ecosystems.
• Detritivores are animals that eat and break down decaying organic matter.
• Decomposers are microorganisms like bacteria and fungi that break down dead matter.
• They secrete enzymes to break down complex compounds into simpler ones, which they absorb.
• Decomposers release carbon dioxide and inorganic mineral nutrients into the environment which are reused by plants.
• Decomposers prevent the buildup of dead matter and recycle nutrients.
• Functions of decomposers:
  • Provide carbon dioxide for respiration.
  • Recycle nutrients back into the soil for plants.
  • Fix nitrogen for plants.
  • Prevent the accumulation of dead organic matter.

Ecological Pyramids

• Ecological pyramids graphically represent the relationship between organisms in different trophic levels.
• The bars in the pyramid denote trophic levels based on who consumes whom, representing energy flow.
• Energy moves upwards, from primary producers to consumers.
• Food chains and ecological pyramids typically have four to five trophic levels due to insufficient energy at higher levels.
• Types of ecological pyramids:
  • Pyramid of Numbers: Represents the number of organisms at each level.
    • Usually decreases from producers to top consumers.
    • Unit: Number of organisms.
  • Pyramid of Biomass: Represents the biomass at each trophic level per unit area.
    • Typically decreases from producers to top consumers.
    • Unit: g/m2 or Kg/m2.
  • Pyramid of Energy: Represents the total energy at each level and energy loss between levels.
    • Always decreases from producers to top consumers.
    • Unit: J/m2/yr (Joules per square meter per year).

Predator-Prey Relationships

• A predator kills and eats another organism.
• Prey is the organism that gets eaten.
• Predators can also be prey for other organisms.
• Apex predators are at the top of the food chain with no predators.
• Predators and prey co-evolve.
• Predators characteristics evolve to catch prey.
• Prey characteristics evolve to avoid predators.
• Predator characteristics:
  • Speed
  • Stealth
  • Camouflage
  • Highly developed Senses
  • Sharp Mouthparts
  • Poison
  • Immunity to Prey's Poison
• Prey characteristics:
  • Speed
  • Rapid Responses
  • Camouflage
  • Highly developed Senses
  • Protective Body Coverings
  • Poison
• Predator-prey relationships maintain balance in ecosystems.
• Overhunting by predators decreases prey populations, leading to a decrease of predator population.
• Biological control uses predator-prey dynamics to manage pests.

Competition

• Habitats have limited resources leading to competition.
• Organisms failing to secure resources may die if they cannot relocate.
• Interspecific competition is competition between different species for resources.
• Intraspecific competition is competition within the same species for resources.
• Animals compete for food, water, shelter, and mates.
• Plants compete for nutrients, sunlight, water, and space.

Symbiosis

• Close relationships between two different species.
• Types of symbiotic relationships:
  • Commensalism: One organism benefits, the other is unaffected.
    • Example: Cattle and egrets.
  • Mutualism: Both organisms benefit.
    • Example: Coral polyps and zooxanthellae (algae).
  • Parasitism: One organism benefits, the other is harmed.
    • Example: Lice, ticks, and fleas on mammals.