Positive interactions occur when neither species is harmed and the benefits of the interaction are greater than the costs for at least one species. Facilitation is a synonym for positive interactions.

Mutualism: Mutually beneficial interaction between individuals of two species (+/+).

Commensalism: Individuals of one species benefit, while individuals of the other species do not benefit and are not harmed (+/0). (Birds cleaning off non-parasitic bugs on large herbivores)

Symbiosis: A relationship in which the two species live in close physiological contact with each other, such as corals and algae.

Symbioses can include parasitism (+/–), commensalism (+/0), and mutualism (+/+).

Most plants form mycorrhizae: Symbiotic associations between the roots and various fungi. (found everywhere- essential for plant evolution on land)

The fungi increase the surface area for the plant to take up water and soil nutrients (over 3 m of fungal hyphae may extend from 1 cm of plant root).

Ectomycorrhizae: The fungus grows between root cells and forms a mantle around the root. Small, multiple roots; thin “worm-like” extensions,

Arbuscular mycorrhizae: The fungus grows into the soil, extending away from the root; and also penetrates into some of the plant root cells. (longer, spine-like sheath root systems)

  • Corals form a mutualism with symbiotic algae.
  • The coral provides the alga with a home, nutrients (nitrogen and phosphorus), and access to sunlight.
  • The alga provides the coral with carbohydrates produced by photosynthesis.
  • Herbivores such as cattle and sheep depend on bacteria and protists that live in their guts to help metabolize cellulose. (mutualism)
  • Another example is mutualism is pollination
  • Wood-eating insects also have gut protists that can digest cellulose.
  • Commensalism is also everywhere.
  • Millions of species form +/0 relationships with organisms that provide habitat.
  • Different types of ecological interactions can evolve into commensalism or mutualism.
  • Mutualism can arise from a host–parasite interaction.
  • Some positive interactions are highly species-specific, and obligate (not optional for either species, rely on each other).
  • Many mutualisms and commensalisms are facultative (not obligate) and show few signs of coevolution.
  • Interactions between two species can be categorized by the outcome for each species:
  • Positive (benefits > costs).
  • Negative (costs > benefits).
  • Neutral (benefits = costs).
  • But costs and benefits can vary.
  • Each partner in a mutualistic interaction acts in ways that serve its own ecological and evolutionary interests.
  • Mutualisms can be categorized by the type of benefits that result.
  • Trophic mutualisms: Mutualist receives energy or nutrients from its partner. (i.e mycorrhizae)
  • Habitat mutualisms: One partner provides the other with shelter, living space, or favorable habitat.
  • Service mutualisms: One partner performs an ecological service for the other. Ecological services include pollination, dispersal, and defense against herbivores, predators, or parasites. (i.e bees pollinating plants)
  • Cheaters are individuals that increase offspring production by overexploiting their mutualistic partner.
  • Positive interactions affect the abundances and distributions of populations as well as the composition of ecological communities.
  • Mutualism and commensalism can increase growth, survival, or reproduction of the interacting species.
  • Positive interactions also influence community composition.
  • Many coral reef fish have service mutualisms with smaller organisms (cleaners) that remove parasites from the fish (clients).

Help Us Fix his Smile with Your Old Essays, It Takes Seconds!

Biotic Relationships: Commensalism, Niche, Parasitism

-We are looking for previous essays, labs and assignments that you aced!

-We will review and post them on our website.
-Ad revenue is used to support children in developing nations.
-We help pay for cleft palate repair surgeries through Operation Smile and Smile Train.

Cite this article as: William Anderson (Schoolworkhelper Editorial Team), "Mutualism and Commensalism," in SchoolWorkHelper, 2019, https://schoolworkhelper.net/mutualism-and-commensalism/.
Inline Feedbacks
View all comments