(4/10.2): Mutualistic Interactions I

Mutualistic Interactions I

• Mutualism is a relationship where both individuals benefit (+ / +).
• Mutualism knowledge dates back to Aristotle but has received less attention than competition and predation.
• Each party in mutualism evolves to benefit the other only if the benefit to themselves outweighs the cost of providing the benefit to the partner.
• If the costs of producing the “gift” outweigh the benefits, the individual should no longer participate in the relationship.
• Mutualism can be considered as reciprocal parasitism.
• Symbiosis is often used synonymously with mutualism but isn't necessarily the same.
• Symbiotic relationships involve partners being together all the time and in almost constant contact.
• Lichens (algae and fungi) have a symbiotic relationship.
• A plant and pollinator might have a mutualistic relationship, but they aren't symbionts if the pollinator visits other plants.

Commensalism

• Commensalism is a relationship where one benefits and the other gets no benefit or cost (+/0).
• Commensalism occurs where one takes advantage of another's existing behavior without affecting that individual.
• Example: Burdock
• Scientists can make incorrect assumptions about relationships due to incomplete information.
• Mutualistic relationships can be mistaken for commensalistic ones because the benefit is not obvious or detectable.
• Sometimes it's assumed that both benefit, but one may not receive any benefit or cost (commensalism).
• Brown-headed Cowbird example.

Mutualism

• Partners in a mutualistic relationship: can partners survive without it? Yes and no.
  • Facultative mutualism: Individuals can exist without their mutualistic partner.
    • Example: Honeyguides in Africa
  • Obligate mutualism: Individuals are so dependent on the relationship that they cannot survive without it.
    • Example: Cellulose-digesting bacteria.
  • "Survive" can mean to live literally or to pass genes onto the next generation (reproduce).
• Mutualism examples:
  • Consider costs and benefits for each partner.
  • When costs to outweigh benefits, the relationship dissolves.
• Ants on Acacia Trees
• Coral Reefs
• Mycorrhizae
• Frugivory
• Rhizobium Nitrogen Fixation
• Consider the state of the world without mutualisms.