Ecology - Mutualism Notes

Definitions

  • Symbiosis: Close, long-term interactions (mutualism, commensalism, parasitism).
  • Mutualism (+,+): Beneficial to both species.
  • Commensalism (+,0): One benefits, the other unaffected.
  • Parasitism (+,-): One benefits, the other harmed.
  • Facilitation: One organism benefits another (mutualism, commensalism).
  • Obligate: Species depends on symbiotic association.
  • Facultative: Species benefits but isn't dependent.

Why Mutualism Exists

  • Benefits outweigh costs for each species.
  • Can evolve from parasitism via reduced harm to host.
  • Evolution favors cooperative partners.
  • Penalties exist for cheaters.
  • High benefit-to-cost ratio reduces cheating incentive.
  • Modeling is system-specific due to complex interactions.

Animal-Animal Interactions

  • Remora and Hosts:
    • Remora gets protection, transportation, food.
    • Eats skin flakes, parasites, feces, scraps.
    • Obligate for Remora, facultative for hosts.
  • Cleaner Fish:
    • Remove parasites, skin flakes from 'clients'.
    • Operate from cleaning stations.
    • Can be obligate (Sharknose goby) or facultative (blue-headed wrasse).
  • Oxpeckers:
    • Eat blood, keep wounds open, possibly parasitic.
    • Impact on ungulates is complex.
  • Gobiid Fishes and Alpheid Shrimps:
    • Shrimp digs burrow, both inhabit.
    • Shrimp is blind, relies on goby for warning.
    • Association evolved multiple times.

Animal-Plant Interactions

  • Pollination:
    • Animals transfer pollen; plants provide reward (pollen, nectar).
  • Yucca Moth and Yucca Plant:
    • Obligate mutualism; yucca relies on moth for pollination.
    • Moth larvae eat some seeds.
  • Fig and Fig Wasps:
    • Ancient, diverse mutualism.
    • Species-specific in many cases.
  • Ants and Acacia Tree:
    • Acacia provides nest sites, food for ants.
    • Ants protect tree from herbivores.
    • Scale insects enhance mutualism.
  • Seed Dispersal:
    • Birds/mammals eat fruit, deposit seeds in dung (Endozoochory).
    • Elephants eat acacia pods, disperse seeds, kill beetle grubs.
    • Ants disperse seeds with elaiosomes (Myrmecochory).
    • Scatter caching by birds/mammals: seeds dispersed by seed predators.

Human Interactions

  • Honeyguides and Humans:
    • Humans open beehives, birds eat remaining comb.
  • Domesticated Species:
    • Mutualism leads to high populations (e.g., chickens, cats, dogs).

Summary

  • Mutualistic relationships are highly evolved and complex.
  • Cheating can occur; partners may be parasitic.
  • Cleaning relationships prevalent in animal interactions.
  • Mutual dependency is common in animal-plant interactions (pollination).
  • Symbiotic interactions are vital for ecosystem function but are easily disrupted.