3.5 - Symbiosis

• Symbiosis


  Close or intimate relationships between members of two different species, usually benefiting at least one individual involved
• Categories of symbiosis


  • Parasitism
  • Mutualism
• Parasitism


  Relationship where one species benefits at the expense of the other, the parasite gains nutrients/energy from the host while harming it
• Mutualism


  Relationship where both species benefit from the interaction
• Parasites


  Benefit by gaining nutrients/energy from the host, often have a limited metabolism and need to spread from host to host
• Parasites cannot survive out of contact with a host
• A tapeworm lacks a digestive system since it lives within its host digestive system
• The most effective parasite is one that does not kill its host completely to ensure a continuous supply of nutrients or energy
• Parasites need to spread from host to host


  Transmitted in various ways: Direct contact, Release of resistant stages, Use of a vector
• Parasite transmission methods


  • Direct contact, Release of resistant stages, Use of a vector
• Some parasites require the use of a secondary host within their life cycle
• Secondary hosts for parasites

  • Fish for the fish tapeworm (Diphyllobothrium latum), Pigs for the pork tapeworm (Taenia solium)
• In mutualism, both species benefit from the interaction in an interdependent relationship
• Mutualism example: Herbivores and cellulose-digesting protozoa/bacteria


  Herbivores provide a warm, moist environment and constant food supply, Protozoa/bacteria break down cellulose and provide a protein source
• Other examples of mutualism

  • 'Cleaner' fish and larger fish, Lichens formed by algae and fungi, Leguminous plants and nitrogen-fixing bacteria