22 mutual ism

8/4/2019 22 Mutual Ism

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Species 1

Species 2

+

+

Each population has a positive effect on the other.

Example: hummingbirdand a hummingbirdpollinated plant:

MUTUALISM (+,+)

0)n(l

0)n(l

1

2

2

1

dN

Nd

dN

Nd


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In interspecific mutualism, species exchange goodsor services beneficial to the other species:

food for food food for services services for services

To be a true mutualism, giving up the goods orservices should represent a cost to the organism.


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Definitions:

Obligate mutualism: both species would not persist without

the other.

Facultative mutualism: both species can live without the

mutualistic species.

Symbiosis: a very close association between two species(living together).

parasitic symbiosis

mutualistic symbiosis (obligate or facultative)


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Plant-pollinator mutualism(food for services)


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One yucca speciescan only be

pollinated by onespecies of moth.

One species ofyucca moth lays itseggs only insideflowers of only onespecies of yucca.

An obligate mutualism.


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Ant-aphid mutualism(food for services)

Ants are protectingaphids from competitorsand predators.

Aphids squirt honeydewthat is eaten by ants.

A facultative mutualism.


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Rhizobium-legume mutualism(food for food)

Plants supply sugars tothe rhizobium bacteriaand shelter against toxiclevels of oxygen.

Rhizobium bacteria fixnitrogen and export it toplants roots.


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Clownfish-sea anemone mutualismBoth species protect the other from their respective predators. The clownfish

has a mucus on its skin that protects from the anemones sting.Service-for service mutualism, facultative


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Termite intestinal flagellate mutualismThe flagellate digests wood and transforms it into food for the termite, the

termite provides a livable habitat to the flagellate.food-for-service mutualism, obligate on both sides


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Mllerian Mimicry(services for services mutualism)

Unpalatable speciesthat look alike allteach their predatorsthe same message.


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Young blue jay is offered the wing of a monarch butterfly.


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Blue jay after eating the monarch wing.


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+Deters predators of both species

Deters predators of both species

+

Mutualism:

All toxic look-alikes benefit each other.


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What should the isoclines of a mutualisticrelationship look like?

N1

N2

competition

N1

N2

mutualism


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N1

N2

K2

K1N1

N2

K1

K2

Mutualists always coexist.

Mutualism is facultative: eachspecies alone has a K.

Both species have higher densities atthe equilibrium when the mutualist isthere than when it is not there.

Negative Ks: neither species can live

on its own. Mutualism is obligate

If the species coexist, it is due to the

stabilizing effect iof competition withother species.

Both species have a minimal viablepopulation size due to the mutualism.


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Spc 1 can exist without spc 2 but notvice versa. Mutualism is obligate onlyfor spc 2, not for spc 1.

Both species coexist or spc 2 goes toextinction and spc 1 to carryingcapacity.

There is a spc 1-dependent minimal

viable population size only for spc 2.

N1

N2

K1

K2


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Theoretical outcomes of two-species mutualism:

Obligate mutualism (neither species can persist on its own):

Coexistence if mutualism is strong.Extinction if mutualism is too weak.

Facultative mutualism (both species can persist on their own):

Stable coexistence at densities above each species single-speciescarrying capacity.

Facultative-obligate mutualism (only one species can persist without theother):

The obligate mutualist always goes extinct if mutualism is too weak.Both species coexist or the obligate mutualist goes extinct,depending on initial densities.


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Deters predators of both species

+

Mutualism:

All toxic look-alikes benefit each other.


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Monarch butterfly(dangerous model)

Viceroy butterfly(harmless mimic)

Batesian Mimicry:A palatable or harmless mimic exploits a non-palatable or

dangerous model


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Milkweed

Monarch caterpillar

The sap of milkweeds containsa mild toxin: cardiac glycoside


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Viceroy
http://muextension.missouri.edu/explore/agguides/pests/ipm1019.htm


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Coral snake (model) King snake (mimic)


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Bumblebee (model)Robber fly (mimic)


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Wasp (model) Beetle mimicMoth mimic Fly mimic


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Viceroy butterfly(mimic)

What kind of a speciesinteraction is this?

Monarch butterfly(model)


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Viceroy butterfly(mimic)


Prevents the predators from learning to avoid

-

Exploitation:The mimic exploits the model

Monarch butterfly(model)


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Milkweed (nectar producing) Lantana (no nectar)

Epidendrum(no nectar)


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Sexual baiting: someorchids mimic female

wasps: male wasps willcopulate, orchids will getpollinated and the waspwill get nothing.


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If cheating in a mutualistic relationship can produce anexploitative relationship,

and if cheating increases the benefit of the cheater,.

Then why are there so many mutualistic speciesrelationships?


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Occasional cheating also occurs withinmutualisms:

Yucca-mothmutualism:sometimes mothslay too many eggsinto the flower.

Some strainsof rhizobium

bacteria donot produceexcessnitrogen.

Why havent these mutualisms disappeared long ago?


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Cheating must be sanctioned(so that the cost of cheating exceeds the benefits of cheating.)

Yucca plants abortfruits with too

many moth larvae.All larvae die.

Rhizobiastrains that do

not exportnitrogen areoxygen starvedby the hostplant and die.


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Summary:

Mutualism is a mutually beneficial ecological interaction between two

species.

In mutualism, species exchange good or services, at a cost to bothparties.

Mutualism is obligate, facultative, or obligate-facultative.

Mutualistic relationships can be precarious: if mutually obligate, onespecies demise leads to the other species demise as well.

There is a strong tendency for cheaters to evolve. For a mutualism to beevolutionarily stable, the cheater must be punished. If the cheater cannotbe effectively punished, the interaction may evolve into an exploitation.

22 mutual ism

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