Organismal Relationships and Competitive Exclusion

Symbiosis: Mutualism, Commensalism, and Parasitism

  • Symbiosis is an association between two organisms that live together.

Mutualism

  • In mutualism, both organisms benefit from the relationship.
  • Example 1: Goby fish and shrimp.
    • Shrimp digs a hole for both to live in.
    • Goby fish warns the nearly blind shrimp of approaching predators by touching it with its tail, prompting both to dart into the hole for protection.
  • Example 2: Clownfish and sea anemone.
    • The sea anemone has stinging properties that the clownfish is immune to due to a special coating.
    • The clownfish uses the sea anemone for protection and as a place to live.
    • The clownfish eats small pieces of undigested material that could harm the anemone.
    • Clownfish feces helps to replace nutrients for the sea anemone.
  • Example 3: Crocodile and Egyptian plover.
    • The plover picks food out of the crocodile's teeth, helping the crocodile avoid infection and keeping its mouth clean.
    • The bird gets food from the crocodile's mouth.

Commensalism

  • In commensalism, one organism benefits, and the other is unaffected by the relationship.
  • Example 1: Shark and remora.
    • Remoras hang around sharks and eat the scraps of food that fall off when the shark kills something.
    • The shark is unaffected by the remoras.
  • Example 2: Barnacles and whales.
    • Barnacles on the skin of a whale collect nutrients as the whale swims through the ocean.
    • The whale is unaffected by the barnacles.

Parasitism

  • In parasitism, one organism benefits, and the other is harmed by the relationship, but not killed immediately.
  • Example 1: Tick and a dog.
    • The tick benefits by drinking the dog's blood.
    • The dog is harmed by losing blood and potentially getting diseases from the tick.
  • Example 2: Tapeworm and a human.
    • The tapeworm steals nutrients from the human's intestines.
    • The human is harmed by nutrient loss.

Comparison of Symbiotic Relationships

  • Mutualism: Both organisms benefit.
  • Commensalism: One organism benefits, the other is unaffected.
  • Parasitism: One organism benefits, the other is harmed.
  • Examples:
    • Mutualism: Clownfish and sea anemone.
    • Commensalism: Shark and remora.
    • Parasitism: Tick and dog.

Human Symbiotic Relationships

  • Humans have symbiotic relationships with bacteria in their gut.
  • These bacteria help digest certain foods and produce certain vitamins.
  • Taking antibiotics can kill these bacteria, requiring reestablishment of the bacteria culture.
  • The bacteria benefit by living in our gut and getting nutrients.
  • We benefit by having certain things like vitamins produced.

Competitive Exclusion and Niches

  • Zebra mussels, an invasive species in the Great Lakes, displace native species by competing for the same resources.

Niche

  • A niche is the role of an organism in an ecosystem, how it makes its living.
  • Competition for niches leads to competitive exclusion.

Competitive Exclusion

  • When two species compete for the same niche, the species that is not as well-suited to the environment will either:
    • Die
    • Relocate to another ecosystem
    • Change to a different niche in the ecosystem
  • Example: Red squirrels and gray squirrels in Britain.
    • The gray squirrel was introduced and is better suited.
    • The red squirrel has become much less common due to competition.

Competitive Exclusion Principle

  • Two organisms cannot fill the same niche in a given ecosystem.
  • Analogy: Only one shortstop can play on a baseball team at a time.

Niche Differentiation

  • If two organisms have similar niches, they can adjust or adapt to fill a slightly different area of that niche.
  • Example: Darwin's finches on the Galapagos Islands.
    • Some finches live on the tops of trees, some in the middle, some on the bottom, and some on the ground.
    • This is because they were competing for the same resources and found different places to survive within the ecosystem.

Adaptation

  • The organism that is best suited for the environment will survive and pass on its genes to future offspring.
  • Over time, this can lead to adaptation and evolution.

Invasive Species

  • An invasive species is a species that has invaded an area that it is not native to.
  • Example 1: Sea lamprey in the Great Lakes.
    • Sea lampreys are jawless fishes that attach to native fish and suck their blood, causing damage to the populations of the native fish.
  • Example 2: Zebra mussel in the Great Lakes.
    • Zebra mussels displace native species and clog draining areas.
  • Example 3: Carp in the United States.
    • Carp are not native to the United States and are displacing many species of fish.

Summary of Organism Interactions

  • Three main types of organism interactions: competition, predation, and symbiosis.
  • Types of symbiosis:
    • Mutualism: benefits both organisms.
    • Commensalism: Benefits one organism without harming or helping the other.
    • Parasitism: Benefits one organism and causes harm to the other without immediately killing it.
  • Competitive exclusion prevents organisms from filling the same niche in an ecosystem and causes organisms to adapt to fill different niches.