Mutualism and Commensalism

mutualism

any long term association between two species that confer mutual fitness benefits to individual members of both species

obligate mutualism

two species that provide fitness benefits to each other and require each other to persist

facultative mutualism

provide fitness benefits to each other but the interaction is not critical to the persistence of either species

generalist mutualist

a species that interacts with many other species

specialist mutualist

a species that interacts with one other species or a few closely related species

seed and pollen mutualism

- birds and mammals disperse seeds via defecation seed burial
- animals benefit from fruit surrounding seed
- plants benefit by having seed moved to favorable germination sites

mast seeding

all trees of a particular species in a given area produce large seed crops simultaneously; alternating years of high and low production

example of mast seeding

oak trees

how do plants choose a dispersal agent?

produce distasteful or toxic fruits in order to be selective about agents

commensalism

A relationship between two organisms in which one organism benefits and the other is unaffected

mycorrhiza

a symbiotic association between fungi and plant roots

What do mycorrhizae do?

produce a network of hyphae, which provides plants with minerals and water from surrounding soil

lichens

represent symbiotic relationships between a fungus and algae

plant-animal mutualism types

defense/protective and dispersive

defense/protective mutualism

animals species receive food and/or shelter from mutualist plant species in return for defending the plant; ex: ants and swollen thorn acacias

dispersive mutualism

- seed dispersal, which creates problems for plants since many dispersers are also seed predators, but can be fixed by mast seeding
- ex: mistletoe bird
- pollination, which mutualism often evolves through species-species coevolution
- ex: Madagascar star orchid and predicta hawkmoth

animal-animal mutualism

clean mutualisms, which can aquatic or terrestrial

aquatic clean mutualism example

cleaner fish

terrestrial clean mutualism example

warthog and mongoose