Food chains

• Food chains


  Organisms within any ecosystem are linked to form food chains based on how they obtain organic food
• Energy flow in ecosystems

  1. Primary producers absorb sunlight energy and convert it into chemical energy, stored in organic food molecules

  2. Some energy is released by producers during respiration

  3. Some energy is passed on through food chains in organic molecules

  4. At each trophic level, energy and biomass are lost in faeces, excretory products, respiration, and heat

  5. Remaining energy is used in growth and repair, then passed to next trophic level

  6. Decomposers release energy from organic matter during respiration

  7. Energy flows from producers to consumers and decomposers in one direction, not recycled

  8. Generally, only 10% of energy from one level is transferred to the next level
• Consumers


  • Herbivores (consume plants)
  • Carnivores (consume animals)
  • Omnivores (consume both plants and animals)
• Trophic levels


  Levels of feeding within a food chain
• Food webs


  Interrelated food chains in an ecosystem
• Any ecosystem usually has more than one primary producer and most consumers have more than one source of food</b>
• Consequently, food chains are interrelated to form food webs
• Ecological pyramids


  • Represent energy, biomass and number of organisms at successive trophic levels
  • Due to loss of energy and biomass, food chains rarely exceed four or five trophic levels
• Predator


  Organism that kills and feeds on another organism
• Prey


  Organism that the predator eats
• Apex predator


  At the top of a food chain and has no predators
• Predator/prey relationships


  Serve as biological controls and keep numbers of organisms relatively constant
• If a predator overhunts its prey, the prey population will decrease, causing the predator population to decrease, then the prey population will increase again
• Biological control


  Introducing a natural predator of a pest into the environment to control the pest
• Detritivores


  Animals that feed on pieces of decomposing organic matter, breaking them down into smaller fragments
• Decomposers


  Micro-organisms that feed saprophytically on dead and waste organic matter, causing it to decompose and releasing carbon dioxide and inorganic mineral nutrients
• Detritivores and decomposers are essential for the recycling of chemical elements within all ecosystems
• Symbiotic relationships


  • Parasitism
  • Commensalism
  • Mutualism
• Parasitism


  One organism (the parasite) gains benefit while the other organism (the host) is harmed
• Commensalism


  One organism (the commensal) gains benefit while the other is neither harmed nor gains
• Commensalism


  • Epiphytes (plants that grow non-parasitically on other plants)
  • Cattle egrets perching on cows
  • Remoras (small fish) attaching to sharks
• Mutualism


  Both organisms gain benefit, and in many cases they cannot survive without each other
• Mutualism


  • Leguminous plants and nitrogen-fixing bacteria
  • Coral polyps and green algae
  • Termites and protozoans in their intestines
• Other interrelationships


  • Camouflage
  • Pollination
  • Support
  • Protection
  • Competition