Ch.15 - Mutualism & Commensalism

Positive interactions

one or both species benefit & neither is harmed

Mutualism

both species benefit (+/+)

Commensalism

one species benefits while the other is unaffected (+/0)

Symbiosis

two species live in close physiological contact with each other

can be mutualism, commensalism, or parasitism

Mycorrhizae

• symbiotic associations btwn plant roots and fungi

• fungi inc surface area for plant to take up water and soil nutrients & plant supplies fungi with carbohydrates

Ectomycorrhizae

fungus grows btwn root cells and forms mantle around root

Arbuscular mycorrhizae

fungus penetrates cell walls of root cells to form a branched network (arbuscule)

Coral bleaching

coral polyps expel algae that live inside their tissues

Effects of coral bleaching

• inc temp

• pollution

• inc exposure to sun & air

What interactions does mutualism usually arise from?

host-parasite interactions

Positive interactions can be:

• obligate

• facultative

Obligate interactions

• required for either species

  • clear signs of coevolution

  • common among mutualistic relationships

Facultative interactions

• not obligatory; optional

  • few signs of coevolution

  • commensalism always facultative for species that doesn’t benefit

What environement are positive interactions most common in?

stressful environments

• ex) high elevations, wetlands, intertidal zones

Three types of mutualism

• trophic mutualism: mutualist receives energy/nutrients from partner

• habitat mutualism: one partner provides shelter for other

• service mutualism: one partner performs ecological service for other

  • pollination, dispersal, defense against other organisms

T/F mutualists are altruistic (they are in it to benefit other organisms)

false; they are in it for their own benefit

Cheaters

individuals inc offspring production by overexploiting their mutualistic partner